Risk of metabolic syndrome in participants within the normal range of alanine aminotransferase: A population-based nationwide study.

This study aimed to investigate the risk of metabolic syndrome (MS) in participants whose alanine aminotransferase (ALT) levels were within the normal range in the general population. A cross-sectional study was conducted using nationally representative samples from the Korea National Health and Nutrition Examination Survey 2007-2015. A total of 43,402 adults (men, 17,535; women, 25,867) with ALT ≤40 U/L without a history of hepatitis B and C, liver cirrhosis, or liver cancer were analyzed. The risk of MS was evaluated according to the ALT level. The prevalence of MS significantly increased as the ALT levels increased. The proportions of MS in men were 12.6%, 25.2%, and 39.7% in the ALT levels of <15, 15~30, and 30~40 U/L, respectively (p < 0.001), and those of women were 7.2%, 23.3%, and 44.7% in the ALT levels of <10, 10~20, and 20~40 U/L, respectively (p < 0.001). There was an ALT-dependent relationship in the risk of MS in participants with normal ALT level after adjustment for age, alcohol intake, and body mass index. The adjusted odds ratio (aOR) of MS in men was 2.48 (95% confidence interval [CI], 2.16-2.85) in an ALT level of 30~40 U/L compared with that in ALT <15 U/L (p < 0.001), and the aOR of MS in women was 2.67 (95% CI, 2.26-3.15) in an ALT level of 20~40 U/L compared with that in ALT <10 U/L (p < 0.001). Although within the normal range of ALT, the risk of MS increases as the ALT levels increase. The ALT level in the general population without a history of chronic liver disease may be a useful marker to evaluate for MS.

Introduction

Metabolic syndrome (MS) is a cluster of conditions that predispose type 2 diabetes mellitus and cardiovascular disease. The prevalence of MS has increased in recent years worldwide [1]. It is noted for its clinical consequences because it is regarded as a precursor of cardiovascular diseases such as coronary artery and cerebrovascular diseases and type 2 diabetes mellitus [2]. MS is an independent risk factor for various cardiovascular conditions such as microvascular dysfunction, coronary calcification and atherosclerosis, myocardial infarction, and heart failure [3].

The measurement of alanine aminotransferase (ALT) level is a fundamental test in screening for liver disease and assessing disease progression. Abnormal serum ALT levels are found in a variety of liver diseases such as viral hepatitis, alcoholic liver disease, or nonalcoholic fatty liver disease (NAFLD). The risk of cardiovascular disease such as ischemic heart disease or type 2 diabetes mellitus also increases in the case of elevated ALT levels [4, 5]. Furthermore, the risk of MS increases in participants with elevated ALT levels [6, 7]. The prevalence and development of MS are associated with the increased ALT levels independently of insulin resistance [8, 9].

Most clinicians carefully examine an abnormal ALT level, while they have little interest in an ALT level within the normal range. However, several studies were conducted to re-evaluate the upper limit of normal (ULN) of ALT and suggested that the new ULN of ALT should be lower than the conventional one (<40 U/L) [10-12]. Some studies suggested that the ULN of ALT in healthy participants are defined as 29–33 and 19–25 U/L in males and females, respectively [13-15]. Therefore, this study planned to investigate the risk of MS in participants with normal ALT levels in the Korean general population using a population-based nationwide data. Furthermore, we evaluated an ALT-dependent relationship in the risk of MS in participants with normal ALT levels.

Methods

Study population

This cross-sectional study was conducted using data from the Korea National Health and Nutrition Examination Survey (KNHANES) between 2007 and 2015. The KNHANES, a nationally representative survey, is performed by the Korea Centers for Disease Control and Prevention (KCDC). It is based on a complex, stratified, multistage, and probability cluster sampling of the noninstitutionalized population in Korea [16]. This survey consists of four parts: health interview, nutrition, health behavior, and health examination surveys. The health interview and examination are performed by trained medical staffs and interviewers at the mobile examination center. The KNHANES has been periodically performed since 1998. This study was conducted using KNHANES IV (2007–2009), V (2010–2012), and VI (2013–2015).

The target population of this survey was all noninstitutionalized Korean civilians older than 1 year of age. The survey was conducted with the sampling units based on gender, age, and geographic areas, which were determined according to the household registries of the Korea National Census Registry. Written informed consent was obtained from all participants in the survey. The KNHANES was approved by the Institutional Review Board of KCDC (2007-02CON-04-P, 2008-04EXP-01-C, 2009-01CON-03-2C, 2010-02CON-21-C, 2011-02CON-06-C, 2012-01EXP-01-2C, 2013-07CON-03-4C, 2013-12EXP-03-5C, and 2015-01-02-6C).

A total of 73,353 participants completed the survey through the mobile health exam units. First, we excluded 24,499 participants according to the following criteria: age under 19 years old (n = 17,314), absence of laboratory data (n = 6,337), and absence of alcohol intake history (n = 848). Of the remaining 48,854 participants, we additionally excluded 2,026 patients with hepatitis B (n = 1,757), hepatitis C (n = 174), liver cirrhosis (n = 79), and liver cancer (n = 16). A total of 46,828 participants without a history of viral hepatitis, cirrhosis, or liver cancer were determined. Finally, 43,402 participants whose ALT levels were within the normal range (≤40 U/L) were included in the final analysis, and we compared them to the remaining 3,426 with ALT level >40 U/L (Fig 1).

Fig 1

Flow diagram of enrolled participants.

Abbreviations: KNHANES, Korea National Health and Nutrition Examination Survey; ALT, alanine aminotransferase.

Clinical variables

The information about alcohol consumption was obtained during the health interview survey. Alcohol consumption was evaluated by questioning the participants about their drinking behavior during the month just before the interview. They were asked for their average frequency (days per month) of alcoholic beverage consumption and average amount (units of drink/day) of alcoholic drinks ingested on a single occasion. Each unit was equivalent to approximately 10 g of alcohol intake.

Blood tests including aspartate aminotransferase (AST); ALT; total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol; and triglyceride were checked after 12 h of fasting. Routine biochemical tests, including triglyceride; glucose; total, HDL, and LDL cholesterol; ALT; and AST, were performed by ADVIA 1650 analyzer (Bayer, Pittsburgh, PA, USA). Hepatitis B surface antigen was measured using an electrochemiluminescence immunoassay method with an E-170 automated analyzer (Roche, Penzberg, Germany). Chemiluminescent microparticle immunoassay was performed to check the antibody to hepatitis C virus (anti-HCV) using ARCHITECT Anti-HCV (ABBOTT Diagnostics Division, Korea/Germany). HCV RNA was measured by real-time polymerase chain reaction using the COBAS AmpliPrep/COBAS TaqMan HCV test (Roche, Penzberg, Germany). The hepatic steatosis index (HSI) was calculated to assess the relationship between the serum ALT levels and fatty liver grade [17]. High-risk alcohol consumption was defined as alcohol intake ≥7 drink-units one time and ≥2 times a week in men or ≥5 drink-units one time and ≥ 2 times a week in women. MS was defined according to the updated National Cholesterol Education Program Adult Treatment Panel III standards [18, 19].

Statistical analysis

All analyses were performed based on gender. Categorical variables are presented as frequencies and percentages, whereas continuous variables are demonstrated as mean value with standard deviation and median value with interquartile range. The linear trend was analyzed between clinical variables and ALT levels categorized by 3 groups (male, ALT, 0–15, 15–30, and 30–40 IU/L; female, ALT, 0–10, 10–20, and 20–40 IU/L). The ALT cutoff level was defined according to the quartile distribution of ALT level (<25, 25–75, and ≥75 percentile). Continuous variables were analyzed by the weighted linear trend in the one-way ANOVA test, while categorical variables were analyzed by the linear-by-linear association in the chi-square test. A multivariable logistic regression model was used to investigate the influence of the ALT levels on MS. The risk of MS are presented as adjusted odds ratio (aOR). Three models were calculated according to each adjusting variable: age in model 1; age and alcohol consumption in model 2; age, alcohol consumption, and body mass index (BMI) in model 3. Multivariable analysis was performed using a forward conditional stepwise procedure to avoid multicollinearity. P values < 0.05 were considered statistically significant. All statistical analyses were performed using SPSS for Window release 18.0 (SPSS Inc., Chicago, IL, USA).

Results

Baseline characteristics of the participants whose ALT levels were within the normal range (≤40 U/L)

Table 1 presents the baseline characteristics of the participants whose ALT levels were within the normal range (≤40 U/L). The mean ages and BMI values of male and female participants were 50.5 and 49.5 years old and 23.8 and 23.3 kg/m2, respectively. The systolic blood pressure (SBP) levels of male and female participants were 121.2 ± 15.9 and 116.4 ± 18.0, and their diastolic blood pressure (DBP) levels were 78.1 ± 10.6 and 73.6 ± 10.0, respectively. The ALT level of male participants was 20.8 ± 7.6 U/L, while that of females participants was 15.9 ± 6.5 U/L. The mean levels of the HSI in male and female participants were 31.6 ± 4.5 and 32.0 ± 4.5, respectively. The prevalence rates of MS in male and female participants were 24.6% and 26.3%, respectively. The proportion of high-risk alcohol consumption in male participants was 18.9%, while that in female participants was 4.2%.

Table 1

Baseline characteristics of the participants.

	Male (n = 17,535)	Female (n = 25,867)
Age (year, mean ± SD)	50.5 ± 16.6	49.5 ± 16.5
Height (cm, mean ± SD)	169.5 ± 6.7	156.6 ± 6.6
Weight (kg, mean ± SD)	68.2 ± 10.4	57.1 ± 8.8
BMI (kg/m2, mean ± SD)	23.8 ± 3.0	23.3 ± 3.4
Waist circumference (cm, mean ± SD)	83.9 ± 8.6	78.5 ± 9.7
SBP (mmHg, mean ± SD)	121.2 ± 15.9	116.4 ± 18.0
DBP (mmHg, mean ± SD)	78.1 ± 10.6	73.6 ± 10.0
AST (U/L, mean ± SD)	22.0 ± 7.4	19.5 ± 5.8
ALT (U/L, mean ± SD)	20.8 ± 7.6	15.9 ± 6.5
FBS (mg/dL, mean ± SD)	100.2 ± 23.7	96.2 ± 21.2
Total cholesterol (mg/dL, mean ± SD)	185.6 ± 34.6	189.5 ± 36.2
HDL cholesterol (mg/dL, mean ± SD)	46.9 ± 11.0	52.0 ± 11.8
Triglyceride (mg/dL, mean ± SD)	148.8 ± 116.9	114.8 ± 77.4
BUN (mg/dL, mean ± SD)	15.4 ± 4.6	13.8 ± 4.4
Creatinine (mg/dL, mean ± SD)	1.0 ± 0.3	0.7 ± 0.2
Hepatic steatosis index	31.6 ± 4.5	32.0 ± 4.5
High-risk alcohol consumption (N, mean ± SD)	3313 (18.9%)	1087 (4.2%)
Diabetes mellitus (N, %)	1558 (8.9%)	1708 (6.6%)
Use of antidiabetic agents	1351 (7.7%)	1543 (6.0%)
Use of lipid-lowering agents	825 (4.7%)	1768 (5.6%)
Use of antihypertensive agents	3295 (18.8%)	4872 (18.8%)
Metabolic syndrome (N, %)	4312 (24.6%)	6809 (26.3%)
Scores of metabolic syndrome0/1/2/3/4/5 (N)	4421/4626/4176/2734/1309/269	6873/6780/5405/3853/2270/686

Abbreviations: SD, standard deviation; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; AST, aspartate aminotransferase; ALT, alanine aminotransferase; FBS, fasting blood sugar; HDL, high-density lipoprotein; BUN, blood urea nitrogen.

Table 2 demonstrates the changes of clinical variables according to the ALT level. There were dose-dependent increases of BMI, waist circumference, SBP, DBP, fasting blood glucose (FBS), total cholesterol, triglyceride, and HSI and prevalence rates of diabetes mellitus and MS as the ALT levels increased in both male and female participants. In addition, the HDL cholesterol level decreased as the ALT levels increased in both groups. In male participants, the proportion of high-risk alcohol consumption increased as the ALT levels increased, whereas that in female participants had an inverse correlation with the increase in the ALT levels.

Table 2

Clinical characteristics of the participants according to the ALT level.

	Male (n = 17,535)				Female (N = 25,867)
	0~15	15~30	30~40	P value for trend	0~10	10~20	20~40	P value for trend
Number of participants (No, %)	n = 3,927	n = 10,916	n = 2,692		n = 3,193	n = 1,6601	n = 6,073
Age (year, mean ± SD)	50.2 ± 19.5	51.1 ± 15.9	48.4 ± 14.7	<0.001	37.6 ± 15.1	49.9 ± 16.4	54.8 ± 14.2	<0.001
BMI (kg/m2, mean ± SD)	22.3 ± 2.7	23.9 ± 2.9	25.3 ± 3.0	<0.001	21.4 ± 2.8	23.1 ± 3.2	24.9 ± 3.6	<0.001
Waist circumference (cm, mean ± SD)	79.9 ± 8.3	84.4 ± 8.2	88.0 ± 8.1	<0.001	72.9 ± 8.2	77.8 ± 9.2	83.2 ± 9.8	<0.001
SBP (mmHg, mean ± SD)	119.0 ± 16.5	121.6 ± 15.7	122.8 ± 15.3	<0.001	107.6 ± 14.5	116.2 ± 17.9	121.7 ± 18.0	<0.001
DBP (mmHg, mean ± SD)	75.2 ± 10.3	78.5 ± 10.3	80.8 ± 10.8	<0.001	69.8 ± 9.1	73.4 ± 9.9	76.1 ± 10.1	<0.001
AST (U/L, mean ± SD)	17.7 ± 4.1	22.1 ± 6.0	28.3 ± 10.8	<0.001	14.8 ± 5.4	18.4 ± 3.9	24.7 ± 6.6	<0.001
ALT (U/L, mean ± SD)	11.8 ± 2.0	20.7 ± 4.1	34.1 ± 3.1	<0.001	8.0 ± 1.2	14.0 ± 2.7	25.5 ± 5.1	<0.001
FBS (mg/dL, mean ± SD)	97.1 ± 22.9	100.4 ± 23.2	103.6 ± 26.0	<0.001	90.1 ± 15.0	95.2 ± 19.7	102.0 ± 26.2	<0.001
Total cholesterol (mg/dL, mean ± SD)	176.6 ± 32.2	187.0 ± 34.1	192.9 ± 37.7	<0.001	176.4 ± 32.7	189.3 ± 35.2	197.0 ± 38.5	<0.001
HDL cholesterol (mg/dL, mean ± SD)	48.4 ± 11.2	46.7 ± 10.9	45.2 ± 10.9	<0.001	54.9 ± 11.6	52.3 ± 11.8	49.6 ± 11.6	<0.001
Triglyceride (mg/dL, mean ± SD)	112.0 ± 75.1	151.2 ± 117.6	192.6 ± 144.6	<0.001	84.7 ± 48.8	109.7 ± 70.3	144.7 ± 96.6	<0.001
Hepatic steatosis index	28.0 ± 3.2	31.9 ± 3.8	35.9 ± 4.3	<0.001	28.0 ± 3.0	31.4 ± 3.8	35.7 ± 4.4	<0.001
High-risk alcohol consumption (N, mean ± SD)	534 (13.6%)	2121 (19.4%)	658 (24.4%)	<0.001	165 (5.2%)	705 (4.2%)	217 (3.6%)	0.001
Diabetes mellitus (N, %)	332 (8.5%)	936 (8.6%)	288 (10.7%)	<0.001	66 (2.1%)	943 (5.7%)	699 (11.5%)	<0.001
Metabolic syndrome (N, %)	495 (12.6%)	2,748 (25.2%)	1,069 (39.7%)	<0.001	231 (7.2%)	3,862 (23.3%)	2,716 (44.7%)	<0.001

Abbreviations: ALT, alanine aminotransferase; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; FBS, fasting blood sugar; HDL, high-density lipoprotein; HSI, hepatic steatosis index.

Prevalence of MS in participants whose ALT levels were within the normal range

Fig 2 presents the prevalence of MS according to the ALT level. In male participants, the prevalence rates of MS were 12.6%, 25.2%, and 39.7% in the ALT levels of 0–15, 15–30, and 30–40 U/L, respectively. A dose-dependent relationship between MS and ALT levels was noted in male participants whose ALT levels were within the normal range (p < 0.001). In female participants, the prevalence rates of MS were 7.2%, 23.3%, and 44.7% in the ALT levels of 0–10, 10–20, and 20–40 U/L, respectively. A dose-dependent relationship between MS and ALT levels was also noted in female participants whose ALT levels were within the normal range (p < 0.001). We also examined the relationship between the score of MS components and ALT levels (Fig 3). Consequently, a positive correlation in the increase of ALT levels and that of MS components was found in both male and female participants, respectively (p < 0.001 and p < 0.001).

Fig 2

The prevalence of metabolic syndrome in patients with ALT ≤40 U/L: Male (A) and female (B). Abbreviation: ALT, alanine aminotransferase.

Fig 3

Differences of the ALT levels according to the sum of the metabolic syndrome scores: Male (A) and female (B). Abbreviation: ALT, alanine aminotransferase.

The relationship between the serum ALT levels and each component of MS in participants whose ALT levels were within the normal range

Table 3 shows the relationship between the serum ALT levels and each component of MS in participants whose ALT levels were within the normal range. In male participants, the serum ALT levels were significantly associated with waist circumference (r = 0.321, p < 0.001), SBP (r = 0.080, p < 0.001), DBP (r = 0.184, p < 0.001), FBS (r = 0.094, p < 0.001), and triglyceride (r = 0.234, p < 0.001). In female participants, the serum ALT levels were also significantly associated with waist circumference (r = 0.343, p < 0.001), SBP (r = 0.227, p < 0.001), DBP (r = 0.185, p < 0.001), FBS (r = 0.195, p < 0.001), and triglyceride (r = 0.269, p < 0.001). An inverse correlation between HDL cholesterol and ALT activity was noted in both male (r = -0.098, p < 0.001) and female (r = -0.140, p < 0.001) participants.

Table 3

Correlations between serum ALT and each components of metabolic syndrome.

	Serum ALT level (U/L)
	Male		Female
Variable	r	P	r	P
Waist circumference (cm)	0.321	<0.001	0.343	<0.001
SBP (mmHg)	0.080	<0.001	0.227	<0.001
DBP (mmHg)	0.184	<0.001	0.185	<0.001
FBS (mg/dL)	0.094	<0.001	0.195	<0.001
Triglyceride (mg/dL)	0.234	<0.001	0.269	<0.001
HDL cholesterol (mg/dL)	-0.098	<0.001	-0.140	<0.001

*Abbreviations: ALT, alanine aminotransferase; SBP, systolic blood pressure; DBP, diastolic blood pressure; FBS, fasting blood sugar; HDL, high density lipoprotein.

‘r’ means the correlation coefficient.

Risk of MS in participants whose ALT levels were within the normal range

Table 4 presents the risk of MS in participants whose ALT levels were within the normal range. We assessed the risk of MS with or without adjustment for the clinical variables: unadjusted and models 1 (age), 2 (age and alcohol consumption), and 3 (age, alcohol consumption, and BMI).

Table 4

Risk of metabolic syndrome in patients whose ALT levels were within the normal range.

Risk of metabolic syndrome	Male					Female
	<15 U/L	15~30 U/L		30~40 U/L		<10 U/L	10~20 U/L		20~40 U/L
	OR	OR	P value	OR	P value	OR	OR	P value	OR	P value
Unadjusted	Reference	2.33 (2.10–2.56)	<0.001	4.57 (4.04–5.16)	<0.001	Reference	3.89 (3.38–4.47)	<0.001	10.37 (9.00–11.97)	<0.001
Model 1	Reference	2.42 (2.18–2.69)	<0.001	5.31 (4.68–6.02)	<0.001	Reference	2.20 (1.90–2.55)	<0.001	5.28 (4.53–6.15)	<0.001
Model 2	Reference	2.37 (2.13–2.64)	<0.001	5.12 (4.51–5.81)	<0.001	Reference	2.20 (1.89–2.55)	<0.001	5.27 (4.52–6.15)	<0.001
Model 3	Reference	1.55 (1.38–1.74)	<0.001	2.48 (2.16–2.85)	<0.001	Reference	1.58 (1.35–1.86)	<0.001	2.67 (2.26–3.15)	<0.001

Abbreviations: ALT, alanine aminotransferase; OR, odds ratio.

Adjusted ORs were calculated in models 1, 2, and 3. The variables for adjustment were age in model 1, age and alcohol consumption in model 2, and age, alcohol consumption, and body mass index in model 3.

In male participants, the risk of MS increased in the ALT level ranges of 15–30 and 30–40 U/L compared with that in ALT<15 U/L, respectively, in the unadjusted model (OR, 2.33 [95% confidence interval {CI}, 2.10–2.56]; OR, 4.57 [95% CI, 4.04–5.16]). It also increased after adjustment for the clinical variables. In model 1, the risk of MS in these participants increased in the ALT level ranges of 15–30 and 30–40 U/L compared with that in ALT <15 U/L, respectively (aOR, 2.42 [95% CI, 2.18–2.69]; aOR, 5.31 [95% CI, 4.68–6.02]). In model 2, it increased in the ALT level ranges of 15–30 and 30–40 U/L compared with that in ALT <15 U/L, respectively (aOR, 2.37 [95% CI, 2.13–2.64]; aOR, 5.12 [95% CI, 4.51–5.81]). Moreover, in model 3, it increased in the ALT level ranges of 15–30 and 30–40 U/L compared with that in ALT <15 U/L, respectively (aOR, 1.55 [95% CI, 1.38–1.74]; aOR, 2.48 [95% CI, 2.16–2.85]).

In female participants, the risk of MS increased in the ALT level ranges of 10–20 and 20–40 U/L compared with that in ALT <10 U/L, respectively, in the unadjusted model (OR, 3.89 [95% CI, 3.38–4.47]; OR, 10.37 [95% CI, 9.00–11.97]). It also increased after adjustment for the clinical variables. In model 1, the risk of MS increased in the ALT level ranges of 10–20 and 20–40 U/L compared with that in ALT <10 U/L, respectively (aOR, 2.20 [95% CI, 1.90–2.55]; aOR, 5.28 [95% CI, 4.53–6.15]). In model 2, it increased in the ALT level ranges of 10–20 and 20–40 U/L compared with that in ALT <10 U/L, respectively (aOR, 2.20 [95% CI, 1.89–2.55; aOR, 5.27 [95% CI, 4.52–6.15]). Moreover, in model 3, it increased in the ALT level ranges of 10–20 and 20–40 U/L compared with that in ALT <10 U/L, respectively (aOR, 1.58 [95% CI, 1.35–1.86]; aOR, 2.67 [95% CI, 2.26–3.15]).

Comparison of the risk of MS between the participants whose ALT levels were within and above the normal range

S1 and S2 Tables show the clinical characteristics of the participants with increased ALT levels (>40 U/L). In male participants, the prevalence rates of MS were 12.6%, 25.2%, 39.7%, and 50.8% in the ALT levels of <15, 15–30, 30–40, and >40 U/L, respectively. A dose-dependent relationship between MS and ALT levels was noted in these participants (p < 0.001). In female participants, the prevalence rates of MS were 7.2%, 23.3%, 44.7%, and 57.8% in the ALT levels of <10, 10–20, 20–40, and >40 U/L, respectively. A dose-dependent relationship between MS and ALT levels was noted in these participants (p < 0.001). Then, we compared the risk of MS between the participants whose ALT levels were within and above the normal range (S3 Table). In male participants, the risk of MS increased in the ALT level ranges of 15–30, 30–40, and >40 U/L compared with that in ALT < 15 U/L, respectively, after adjustment for age, alcohol consumption, and BMI (aOR, 1.57 [95% CI, 1.40–1.76]; aOR, 2.54 [95% CI, 2.21–2.92]; and aOR, 3.63 [95% CI, 3.14–4.19], respectively). In female participants, the risk of MS increased in the ALT level ranges of 10–20, 20–40, and >40 U/L compared with that in ALT <10 U/L, respectively, after adjustment for age, alcohol consumption, and BMI (aOR, 1.59 [95% CI, 1.36–1.87]; aOR, 2.69 [95% CI, 2.28–3.18]; and aOR, 4.28 [95% CI, 3.46–5.31], respectively).

Discussion

The present study investigated the risk of MS in participants without chronic liver disease and whose ALT levels were within the normal range (≤40 U/L) in the Korean general population. The prevalence of MS significantly increased as the ALT levels increased. There was an ALT-dependent relationship in the risk of MS in participants with normal ALT levels after adjustment for age, alcohol intake, and BMI.

The measurement of ALT, one of the many liver enzymes, is a widely used test for liver injury and applied in several clinical situations (acute and chronic liver disease, health checkup, preoperative examination, etc.). The ALT levels provide a basic clue to determine the presence of liver diseases including viral hepatitis, alcoholic liver disease, drug-induced liver injury, and NAFLD. Although ALT is perceived mainly as a liver enzyme, their increased levels are also associated with cardiovascular as well as liver diseases. In addition, such levels predict the development of type 2 diabetes mellitus and coronary heart disease [20,21] and are related to hypoxia in patients with obstructive sleep apnea [22] and associated with intracerebral hemorrhage [23].

MS is a cluster of clinical and laboratory findings consisting of high BMI, blood pressure, and glucose and triglyceride levels and low HDL level [24]. A meta-analysis showed that participants with MS have a twofold increased risk of cardiovascular disease, myocardial infarction, stroke, and cardiovascular disease-related mortality compared with those without MS [25]. MS is associated with increased ALT levels [8,9]. An Australian population-based cohort study showed that the ALT levels were strongly associated with the prevalence of MS [26]. A population-based Hispanic cohort study revealed that high prevalence rates of MS were observed in participants with increased ALT levels and male ones had increased ALT levels compared with the females [27]. A Chinese population-based cohort study demonstrated that the longitudinal increments of the ALT levels were related to an increased incidence of MS [28]. MS is related to an elevated ALT level in patients with diabetes mellitus [29]. Also, it is well known that MS is closely related to NAFLD. The prevalence of MS in patients with NAFLD increases as the BMI increases [30]. Furthermore, the increased ALT levels are significantly associated with MS in patients with NAFLD and viral hepatitis [31,32].

This study investigated the risk of MS in participants whose ALT levels were within the normal range (≤40 U/L). The prevalence rates of MS were 24.6% and 26.3% in male and female participants, respectively. Also, the proportions of MS in male and female participants whose ALT levels were within the ULN (male, 30~40 U/L; female, 20~40 U/L) were 39.7% and 44.7%, respectively. The prevalence rate of MS was approximately 40% in the Chinese general population with an ALT level within the normal range (≤40 U/L) [33]. The ALT level within the normal range (≤40 U/L) is closely correlated with the severity of MS in a population-based cohort in Germany [34]. The risk of MS is associated with increased ALT levels within the normal range (≤43 U/L) in the Korean population study [35]. Arterial stiffness and MS were related to the ALT levels within the normal range (≤40 U/L) regardless of alcoholic consumption [36]. The present study also examined the relationship between the score of MS components and ALT levels within the normal range (≤40 U/L). The ALT level significantly increased as the score of MS components increased. Considering the results of the aforementioned and present study, the risk of MS exists even in participants whose ALT levels were within the normal range. Moreover, there is an ALT-dependent relationship in the risk of MS in participants with normal ALT level. Similarly, the risk of liver disease can still exist even if the ALT level is within the normal range. The risk of disease progression is also still noted in patients with chronic hepatitis B or C despite having ALT levels within the normal range [10,11]. Also, the majority of patients with NAFLD (~80%) have ALT levels within the normal range levels [37]. Amarapurkar et al. reported that an abnormal ALT level is observed in 16% of patients with NAFLD diagnosed by ultrasonography [38].

This study has several limitations. Firstly, imaging study or liver biopsy was not checked. Therefore, this study has limitations in detailed information for liver diseases such as hepatic steatosis or liver cirrhosis. Secondly, the relationship between MS and the ALT level change was not evaluated because the present study was conducted based on a cross-sectional study design. Finally, the association between the serum ALT levels and inflammatory markers such as tumor necrosis factor-alpha, plasminogen activator inhibitor 1, interleukin-6, leptin, and adiponectin was not elucidated. In spite of these limitations, this study investigated the relationship between MS and a normal ALT level in a large-scale general population.

Conclusions

In conclusion, the risk of MS significantly increases as the ALT level increases within the normal ALT level. Even if the ALT level is within the normal range, it may be a useful marker to consider the presence of MS.

(DOCX)

Click here for additional data file.

Clinical characteristics of the participants according to ALT level.

(DOCX)

Click here for additional data file.

Risk of metabolic syndrome according to serum ALT level.

(DOCX)

Click here for additional data file.

24 Jan 2020

PONE-D-19-34865

Risk of metabolic syndrome in subjects with a normal range of alanine aminotransferase: a population-based nationwide study

PLOS ONE

Dear Dr Sohn,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

We would appreciate receiving your revised manuscript by Mar 09 2020 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. This file should be uploaded as separate file and labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Ming-Lung Yu, MD, PhD

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements:

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at http://www.plosone.org/attachments/PLOSOne_formatting_sample_main_body.pdf and http://www.plosone.org/attachments/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. Thank you for stating the following on the Title page of your manuscript:

"This study was supported by research fund from Chosun University, 2016. The fund had no role in study design, data collection and analysis, decision to publish,

or preparation of the manuscript."

We note that you have provided funding information that is not currently declared in your Funding Statement. However, funding information should not appear in the Acknowledgments section or other areas of your manuscript. We will only publish funding information present in the Funding Statement section of the online submission form.

Please remove any funding-related text from the manuscript and let us know how you would like to update your Funding Statement. Currently, your Funding Statement reads as follows:

"The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The community-based study included 43402 adults with ALT<=40 U/L to investigate the associations between serum ALT levels and metabolic syndrome (MS). They found that the prevalence of MS increased with serum ALT levels. In addition, the probability of MS increased with serum ALT levels with dose-response trends. The authors concluded that ALT could be used as a marker to evaluate MS, particularly in a general population with normal ALT levels.

The work is clear and straightforward. However, there are still some comments:

1. Although the work is interesting, the clinical utility is limited. There is already clear definitions for MS as the authors indicated in the methods (MS was defined by the updated National Cholesterol Education Program Adult Treatment Panel III standards). Are there any benefits by considering ALT? By including ALT, is it superior to the original definition?

2. It will be interesting to know whether serum ALT levels was correlated to any inflammatory markers or not.

3. It is suggested to calculate fatty liver index and examine the associations between ALT and FLI.

Reviewer #2: The authors aimed to investigate the risk of metabolic syndrome (MS) in subjects with normal ALT level in the general population. They concluded that despite within the normal range of ALT, the risk of MS increased as the ALT levels increased. In general, the topic of this work is interesting. However, some issues should be further reconsidered or corrected.

1. The authors should provide the complete data of metabolic syndrome including systolic and diastolic blood pressure. Also, the correlation of each component of metabolic syndrome with serum ALT level should be evaluated.

2. The subjects with elevated ALT levels should not be excluded and could serve as positive controls.

3. The information of medication history including anti-diabetics, statin and anti-hypertensive drugs should be provided.

4. It is noted that the manuscript is filled with some grammatical errors that need to be corrected.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

20 Feb 2020

Reviewer #1: The community-based study included 43402 adults with ALT<=40 U/L to investigate the associations between serum ALT levels and metabolic syndrome (MS). They found that the prevalence of MS increased with serum ALT levels. In addition, the probability of MS increased with serum ALT levels with dose-response trends. The authors concluded that ALT could be used as a marker to evaluate MS, particularly in a general population with normal ALT levels.

The work is clear and straightforward. However, there are still some comments:

1. Although the work is interesting, the clinical utility is limited. There is already clear definitions for MS as the authors indicated in the methods (MS was defined by the updated National Cholesterol Education Program Adult Treatment Panel III standards). Are there any benefits by considering ALT? By including ALT, is it superior to the original definition?

: We appreciate your valuable comment. The aim of the study was to investigate the association between serum ALT and MS. The results of our study cannot imply that the addition of ALT in the diagnostic criteria of MS would be superior to the current standards. However, ALT is a basic laboratory test done frequently in the daily clinic and increases in ALT can be a useful marker that implies the presence of MS.

2. It will be interesting to know whether serum ALT levels was correlated to any inflammatory markers or not.

: Thank you for your comment. Unfortunately, the present study did not check inflammatory markers such as tumor necrosis factor-alpha (TNF-α), plasminogen activator inhibitor 1 (PAI-1), interleukin-6 (IL-6), leptin or adiponectin. We added this limitation in the discussion section of the revised manuscript (page 14).

� Finally, the present study did not clarify the association between serum ALT level and the inflammatory markers such as tumor necrosis factor-alpha (TNF-α), plasminogen activator inhibitor 1 (PAI-1), interleukin-6 (IL-6), leptin and adiponectin.

3. It is suggested to calculate fatty liver index and examine the associations between ALT and FLI.

: We appreciate your valuable comment. As you commented, we newly analyzed the relationship between serum ALT and fatty liver. However, we could not calculate the fatty liver index (FLI) because our data did not include γ-glutamyl-transferase. Fatty liver index consists of triglyceride, BMI, γ-glutamyl-transferase and waist circumference. Therefore, we calculated the hepatic steatosis index (HSI) instead of the fatty liver index (FLI). HSI consists of ALT, AST, BMI, diabetes, and sex (Dig Liver Dis 2010;42:503-8.). We analyzed the association between ALT level and HSI. There was a dose-dependent increase of HSI as ALT levels increased in both male and female subjects (Table 2). In male subjects, HSI was 28.0 ± 3.2, 31.9 ± 3.8 and 35.9 ± 4.3 in ALT 0-15 U/L, 15-30 U/L, and 30-40 U/L, respectively (p<0.001). In female subjects, HSI was 28.0 ± 3.0, 31.4 ± 3.8 and 35.7 ± 4.4 in ALT <10 U/L, 10-20 U/L, 20-40 U/L and >40 U/L, respectively (p<0.001). We added these findings in the method section and results section of the revised manuscript (page 7 & 8 and Table 2).

� “Hepatic steatosis index (HSI) was calculated to assess the relationship between serum ALT level and fatty liver.” (page 7)

� “The mean level of HSI in male and female subjects was 31.6 ± 4.5 and 32.0 ± 4.5, respectively.” (page 8)

� There were dose-dependent increases of BMI, waist circumference, SBP, DBP, fasting blood glucose (FBS), total cholesterol, triglyceride, HSI, the prevalence of diabetes mellitus, and the prevalence of MS as ALT level increased in both male and female subjects.

Reviewer #2: The authors aimed to investigate the risk of metabolic syndrome (MS) in subjects with normal ALT level in the general population. They concluded that despite within the normal range of ALT, the risk of MS increased as the ALT levels increased. In general, the topic of this work is interesting. However, some issues should be further reconsidered or corrected.

1. The authors should provide the complete data of metabolic syndrome including systolic and diastolic blood pressure. Also, the correlation of each component of metabolic syndrome with serum ALT level should be evaluated.

: According to your comments, we added the data for systolic and diastolic blood pressure in the results section and Table 1 & 2 of the revised manuscript (page 8)

� “Systolic blood pressure (SBP) of male and female subjects was 121.2 ± 15.9 and 116.4 ± 18.0, respectively. Diastolic blood pressure (DBP) of male and female subjects was 78.1 ± 10.6 and 73.6 ± 10.0, respectively.”

Also, we analyzed the correlation of each component of metabolic syndrome with the serum ALT level (Table 4). We added these results in table 4 of the revised manuscript (page 9-10).

� “The relationship between serum ALT level and each component of MS in subjects with a normal range of ALT are shown in Table 4. In male subjects, serum ALT level were significantly associated with waist circumference (r=0.321, p<0.001), SBP (r=0.080, p<0.001), DBP (r=0.184, p<0.001), FBS (r=0.094, p<0.001), and triglyceride (r=0.234, p<0.001). In female subjects, serum ALT level were significantly associated with waist circumference (r=0.343, p<0.001), SBP (r=0.227, p<0.001), DBP (r=0.185, p<0.001), FBS (r=0.195, p<0.001), and triglyceride (r=0.269, p<0.001). There was an inverse correlation between HDL cholesterol and ALT activity in both male (r=-0.098, p<0.001) and female (r=-0.140, p<0.001).”

2. The subjects with elevated ALT levels should not be excluded and could serve as positive controls.

: According to your comments, we added the data for the subjects with elevated ALT levels in the method section, results section, and supplementary document of the revised manuscript (page 6).

� “Finally, 43,402 subjects within the normal range of alanine aminotransferase (ALT ≤40 U/L) were included in the final analysis and we compared these subjects to 3,426 subjects with ALT level >40 U/L (Figure 1).”

We also compared the risk of metabolic syndrome the subjects with normal range and abnormal range of ALT (page 11-12).

� “Clinical characteristics of the subjects with an abnormal range of ALT (>40 U/L) are presented in Supplementary table 1 and 2. In male subjects, the prevalence of MS was 12.6%, 25.2%, 39.7% and 50.8% in ALT <15 U/L, 15-30 U/L, 30-40 U/L and >40 U/L, respectively. There was a dose-dependent relationship between MS and ALT level in male subjects (p<0.001). In female subjects, the prevalence of MS was 7.2%, 23.3%, 44.7% and 57.8% in ALT <10 U/L, 10-20 U/L, 20-40 U/L and >40 U/L, respectively. There was a dose-dependent relationship between MS and ALT level in female subjects (p<0.001). We compared the risk of MS between the subjects with normal range and abnormal range of ALT (Supplementary table 3). The risk of MS in male subjects is increased when in ALT 15-30 U/L, 30-40 U/L, and >40 U/L compared to ALT<15 U/L, respectively in adjusting age, alcohol consumption, and BMI (aOR 1.57 with 95% CI: 1.40-1.76, aOR 2.54 with 95% CI: 2.21-2.92 and aOR 3.63 with 95% CI: 3.14-4.19, respectively). The risk of MS in female subjects is increased when in ALT 10-20 U/L, 20-40 U/L, and >40 U/L compared to ALT<10 U/L, respectively in adjusting age, alcohol consumption, and BMI (aOR 1.59 with 95% CI: 1.36-1.87, aOR 2.69 with 95% CI: 2.28-3.18 and aOR 4.28 with 95% CI: 3.46-5.31, respectively).”

3. The information of medication history including anti-diabetics, statin and anti-hypertensive drugs should be provided.

: As you commented, we added the information regarding the use of anti-diabetic agents, lipid lowering agents, and anti-hypertensive agents. The proportion of the usage of anti-diabetic agents in male and female subjects was 7.7% and 6.0%, respectively. The proportion of the usage of lipid lowering agents in male and female subjects was 4.7% and 5.6%, respectively. The proportion of the usage of anti-hypertensive agents in male and female subjects was 18.8% and 18.8%, respectively. We added these results in Table 1 of the revised manuscript.

4. It is noted that the manuscript is filled with some grammatical errors that need to be corrected.

: As you have commented, the manuscript has been edited for grammatical errors.

Submitted filename: Response to reviewers.docx

Click here for additional data file.

17 Mar 2020

PONE-D-19-34865R1

Risk of metabolic syndrome in subjects within the normal range of alanine aminotransferase: a population-based nationwide study

PLOS ONE

Dear Dr Sohn,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

The English should be revised by native English speakers.

==============================

We would appreciate receiving your revised manuscript by May 01 2020 11:59PM. When you are ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter.

To enhance the reproducibility of your results, we recommend that if applicable you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). This letter should be uploaded as separate file and labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. This file should be uploaded as separate file and labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. This file should be uploaded as separate file and labeled 'Manuscript'.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

We look forward to receiving your revised manuscript.

Kind regards,

Ming-Lung Yu, MD, PhD

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: all comments have been addressed adequately. It is suggested that the article could be polished by an English editor before formal publication.

Reviewer #2: The authors aimed to investigate the risk of metabolic syndrome (MS) in subjects with normal ALT level in the general population. In general, this is an interesting topic and a clearly written paper. Also, the authors have well responded to the reviewer’s suggestions.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files to be viewed.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org. Please note that Supporting Information files do not need this step.

23 Mar 2020

Editor’s comment: The English should be revised by native English speakers.

: We appreciate your valuable comment. According to your comment, the revised manuscript was examined by an English editing service (www.editage.co.kr).

Reviewer #1: all comments have been addressed adequately. It is suggested that the article could be polished by an English editor before formal publication.

: We appreciate your valuable comment. According to your comment, the revised manuscript was examined by an English editing service (www.editage.co.kr).

Reviewer #2: The authors aimed to investigate the risk of metabolic syndrome (MS) in subjects with normal ALT level in the general population. In general, this is an interesting topic and a clearly written paper. Also, the authors have well responded to the reviewer’s suggestions.

: We appreciate your valuable comment.

Submitted filename: Response to reviewers.docx

Click here for additional data file.

25 Mar 2020

Risk of metabolic syndrome in participants within the normal range of alanine aminotransferase: a population-based nationwide study

PONE-D-19-34865R2

Dear Dr. Sohn,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

Shortly after the formal acceptance letter is sent, an invoice for payment will follow. To ensure an efficient production and billing process, please log into Editorial Manager at https://www.editorialmanager.com/pone/, click the "Update My Information" link at the top of the page, and update your user information. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, you must inform our press team as soon as possible and no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

With kind regards,

Ming-Lung Yu, MD, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

27 Mar 2020

PONE-D-19-34865R2

Risk of metabolic syndrome in participants within the normal range of alanine aminotransferase: a population-based nationwide study

Dear Dr. Sohn:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

For any other questions or concerns, please email plosone@plos.org.

Thank you for submitting your work to PLOS ONE.

With kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Ming-Lung Yu

Academic Editor

PLOS ONE