Effect of body mass index (BMI) on pulmonary functions in children of 6-14 years of age: A cross-sectional study.

Background: Over-weight/obesity is a new global pandemic affecting children with prevalence up to 36%. It is responsible for metabolic syndrome and its future complications in children; however, its effect on lung functions in children is not well studied. Aim: To compare lung function tests [forced expiratory volume in the first second (FEV1), FEV1/forced vital capacity (FVC), FVC, and % predicted] of children with over-weight/obesity to that of normal children. Method: it is a hospital-based cross-sectional study. Children of 6-14 years of age with over-weight [body mass index (BMI) >85th centile] and obesity (BMI >95th centile) attending the pediatrics outpatient department (OPD) were included. Age-matched children attending the OPD during the study period were selected as controls. Demographic and anthropometric details were collected, and pulmonary function tests were carried out in included children.
Results: A total of 103 children were included (over-weight/obese = 56, control = 47). The percent predicted (%) FEV1 (86.23 ± 12.84 vs 91.77 ± 8.68) and FVC (81.93 ± 12.12 vs 88.62 ± 10.87) were significantly lower in the obese/over-weight group as compared to control group. A signification negative correlation was found between FEV1 (%) and FVC (%) and that of BMI and waist-hip ratio (WHR). Conclusions: Pulmonary functions (FEV1, FVC) are found to be negatively correlated with BMI and WHR. Copyright:

Introduction

Over-weight/obesity has become a global pandemic affecting children of all age groups. In the United States (USA), approximately 60% of adults and 25% of children and adolescents can be classified as over-weight/obese.[12] Although more studies are needed to ascertain the prevalence of over-weight/obesity in India, the prevalence varies from 7.4% to 36% in different studies.[345] Childhood obesity has both short- and long-term health concerns including metabolic syndrome, cardiovascular disease, and type 2 diabetes mellitus during the adolescent period and adulthood.[35]

The increase in weight gain (over-weight/obesity) is associated with impairment of pulmonary functions at all age groups. There is increased risk of asthma in children with obesity as compared to controls as reported by Lang et al.[6] Studies have revealed a significant reduction in forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), flow rates [peak expiratory flow rate (PEFR) and forced expiratory flow (FEF25–75%)], maximum voluntary ventilation (MVV), expiratory reserve volume (ERV), and functional residual capacity (FRC) associated with morbid obesity.[7] Reductions in pulmonary functions in relation to the waist-to-hip ratio (WHR) have been observed in adults with obesity.[8] A significant decrease in FRC, ERV, flow rates, and MVV has also been found in children and adolescents with over-weight/obesity.[910] A systemic review has shown association between decreased spirometric values (FEV1 and FVC) in children and adolescents with overweight/obesity.[11] However, it does not reach to a consensus on lung function changes among obese children and adolescents and hence recommended for further studies.

Previously published studies have included children with obesity and morbid obesity, whereas data in children with over-weight are limited. Although there are enough data on rapidly increasing prevalence of over-weight/obesity in Indian children as per the National Family Health Survey 2015–2016, its long-term effects are not well studied. As obesity is increasing in both urban and rural India, it is important for primary care physicians to know the various adverse effect of obesity. More emphasis has been given on the metabolic complications related to obesity, whereas its effect on pulmonary functions is lacking in children with over-weight/obesity.[3] As there is also a rise in prevalence of asthma and other respiratory illness among children, it is important to understand the link between obesity and pulmonary functions. It will help not only in better management but also for preventive measures. The primary objective of the present study is to compare pulmonary functions (FEV1, FEV1/FVC, and % predicted) in children with over-weight/obesity to that of normal children in the 6–14 years age group.

Materials and Methods

Children of 6–14 years of age presenting to the pediatric outpatient department (OPD) of a tertiary care teaching hospital of Eastern India with a body mass index (BMI) of >85th centile were included over a 1-year period (March 2017 to 2018). Those with uncontrolled asthma, heart disease, neuromuscular disease, chest deformity, intellectual disability, and acute respiratory symptoms at presentation were excluded. Details of demographic data were collected after taking proper consent from the parents (and assent wherever applicable). A complete physical examination was performed.

Anthropometric parameters (weight, height, waist, and hip circumference) were measured with light clothings without shoes: weight to the nearest 100 g, height (using a stadiometer) to the nearest centimeter (cm), waist circumference (cm) at the mid-point between the costal margin and iliac crest in the mid-axillary line, and hip circumference (cm) at the prominence of buttocks. Blood pressure (BP) was measured with a standardized digital instrument in the right arm in the sitting position three times (0-, 5-, and 30-minute intervals), and the average was taken. BMI was calculated (kg/m2) as per the standard formula and classified into over-weight or obesity as described previously.[12]

A brief questionnaire was administered regarding features of asthma and allergic rhinitis (questionnaire modified from The International Study of Asthma and Allergies in Childhood (ISAAC)) along with perception of obesity; parental history of obesity; and habits like hours of watching television, daily physical activity, etc.

Fasting blood sugar, the liver function test, the lipid profile, and the thyroid profile were measured in children with over-weight/obesity. Children were demonstrated regarding performing the lung function tests (spirometry) in the department of pulmonary medicine as per the guidelines laid down by the American Thoracic Society.[13] For the measurement of FVC, children were asked to take a deep breath and then breath out as rapidly as and as long as possible into the mouth of the spirometer. The flow volume curve was plotted with the best of three acceptable manoeuvers being taken as the final reading. The following parameters were recorded [FVC, FEV1, and FEV1/FVC].

Statistical analysis

Sample size was calculated from available data from a previous study comparing the pulmonary function test in children with over-weight/obesity as compared to normal BMI. Taking into consideration of mean FEV1 (2.2 L ± 0.28) in normal weight as compared to that in children with over-weight/obesity (2.05 L ± 0.28) with a power of 80% and an a-error of 5%, the sample size was calculated to be 55 in each group. Continuous variables were expressed as mean ± SD (standard deviation), and categorical variables were expressed as frequencies and percentages. The data were compared using Student’s t-test. Correlation between pulmonary functions and anthropometry was studied using Spearman correlation coefficient (r).

Results

A total of 103 children (over-weight/obese = 56, control = 47) were included. Of 56 children with obesity/over-weight, 42 (73%) were boys. Among controls, 25 (53%) were boys. The mean (± SD) age of children with obesity/over-weight was 10.6 (± 2.33) years compared to 10.1 (± 2.37) years among the controls. The mean (± SD) weight of the control group was 32.4 (± 6.64) kg, and that of the obese/over-weight group was 56.5 (± 12.8) kg. The mean height (± SD) of the control and obese/over-weight group was 139 (± 9) cm and 142 (± 12) cm, respectively. The BMI of the obese/over-weight group was 26.62 (± 3.78) kg/m2, whereas that of the control group was 16.55 (± 1.75) kg/m2. The waist-hip ratio (WHR) in the obese/over-weight group was 0.96, whereas in the control group, it was 0.90 [Table 1].

Table 1

Baseline parameters of the study population

	Obese/over- weight (n=56)	Control (n=47)
Age (years)	10.6±2.33	10.1±2.37
Sex*
Boys, n (%)	42 (73)	25 (53)
Girls, n (%)	14 (27)	22 (47)
Weight (kg)	56.5±12.8	32.4±6.64
Height (cm)	142±12	139±9
BMI (kg/m2)	26.62±3.78	16.55±1.75
W: H ratio (WHR) (cm)	0.96±0.05	0.90±0.02
Birth weight (kg)	2.87±0.47	2.87±0.38
SBP (mm hg)	105±10	98±8
DBP (mm hg)	66±8	64±10

Data are expressed as mean±SD unless specified otherwise. SBP: systolic BP and DBP=diastolic BP. *Expressed in percentage (%)

Pulmonary function test was carried out in all the included children. The mean (± SD) FVC in the obese/over-weight group was 1.91 L (± 0.48), whereas that of the normal group was 2.01 L (± 0.51). Although children with obesity/over-weight have a lower FVC as compared to the control group, it was not statistically significant. Similarly, the mean (± SD) FEV1 in the control group (1.85 L ± 0.42) was higher than the obese/over-weight group (1.76 L ± 0.44) but was not again statistically significant. However, the percentage (%) predicted FEV1 and FVC were significantly different between the two groups [Table 2].

Table 2

Pulmonary function between the obese/ over-weight and control groups

Parameters	Obesity	Normal	P
FEV1 (L)	1.76±0.44	1.85±0.42	0.30
FEV1 (%)	86.23±12.84	91.77±8.68	0.01*
FVC (L)	1.91±0.48	2.01±0.51	0.29
FVC (%)	81.93±12.12	88.62±10.87	0.004*
FEV1/FVC	92.65±8	92.33±7.99	0.84
FEV1/FVC (%)	105.93±8.32	105.51±9.03	0.80

*P significant (<0.05)

We also tried to find out correlation between pulmonary functions (FVC, FEV1, and FEV1/FVC) and various factors such as height, weight, BMI, and WHR. The results are presented in Table 3. We found a negative correlation between FVC and FEV1 with BMI and WHR but a positive correlation between weight and height. None of these correlations were statistically significant. However, we found a significant negative correlation between percent (%) predicted FEV1 and FVC with that of BMI and WHR.

Table 3

Correlation between pulmonary functions and BMI, weight, height, and WHR

Parameters	FVC	%FVC	FEV1	%FEV1	FEV1/FVC	%FEV1/FVC
BMI (ρ)	-0.029 (0.77)	-0.2735 (0.005)*	-0.33 (P=0.73)	-0.2717 (0.005)*	-0.01 (0.91)	-0.0354 (0.71)
Weight (ρ)	0.29 (0.002)*	-0.2512 (0.01)*	0.31 (P=0.001)*	-0.225 (0.02)*	-0.0019 (0.98)	-0.0019 (0.98)
Height (ρ)	0.68 (0.0001)*	-0.023 (0.81)	0.70 (P=0.001)*	0.0056 (0.95)	-0.0498 (0.62)	-0.0023 (0.98)
WHR (ρ)	-0.56 (0.57)	-0.2452 (P=0.012)*	-0.05 (P=0.61)	-0.2011 (0.04)*	0.0359 (0.71)	0.0666 (0.50)

P in brackets (*significant at <0.05)

Discussion

In the present study, the percent predicted (%) FEV1 (86.23 ± 12.84 vs 91.77 ± 8.68) and FVC (81.93 ± 12.12 vs 88.62 ± 10.87) were significantly lower in the obese/over-weight group as compared to the control group. A significant negative correlation was also found between FEV1 (%) and FVC (%) and that of BMI and WHR.

Children with over-weight and obesity may have variables which differ from that of children with normal BMI including metabolic parameters and lung functions. Obesity causing reduction of reserve volume and FVC is well established in adult studies. However, the results in children are conflicting. There is no change in vital capacity, lung compliance, and residual volume in children with obesity in some studies,[14151617] whereas in others, there is a reduction of residual lung volume in children with obesity.[818] A study done by Torun et al.[16] in children and adolescents between age 9 and 17 years, which comprised both obese and non-obese children showed that there was no significant difference in FVC, FEV1, or FEV1/FVC when compared between lean normal weight, over-weight, obese, and morbid obese children. However, a similar study in children of age 6–12 years by Muñoz et al.[18] showed a lower FRC in obese children as compared to non-obese children, which was negatively correlated with WHR. Similarly, an increased weight and an increased BMI in children were associated with increased FEV1 and FVC and reduced FEV1/FVC in a study conducted in Asian children by Yao et al.[19] Although this study included 1717 children from age 5 to 18 years, it was a cross-sectional study and did not compare pulmonary functions among obese/over-weight and normal weight children. In a study by Paralikar et al.,[20] the mean % predicted FEV1, the mean absolute value, and the % predicted FEV1/FVC and MVV values were similarly lower in children with obesity. This study was conducted in children of age 12–17 years where they compared pulmonary function indices on 30 obese children with age-matched controls. This is one among a few studies where the lung function was compared with controls as in ours, although done mostly in the adolescent age group.

In the present study, we did not find any statistically significant difference in FEV1 among obese/over-weight children versus that of children in the control group. Similarly, we could not document any difference between FVC and FEV1/FVC unlike some of the previously published studies showing statistically significant lower FEV1 and FVC among children with obesity. Nageswari et al.[21] reported lower FEV1 and FVC in obese children as compared to controls of age 12–16 years, although the sample size was 20 in each group. However, Cibella et al.[22] reported a similar result in a cross-sectional study. However, we found a significant difference between FEV1 (%) and FVC (%) among children with obesity and those in the control group. Both FEV1 and FVC were lower in children with obesity compared to controls, which was similar to a previously published cross-sectional study by Ulger et al.[23] done in children with obesity between 9 and 15 years of age. Another study found similar results to the present study, where there was no significant difference in FEV1, FVC, or FEV1/FVC, but significant reductions were noted in PEF and FEV25–75 in the over-weight, obese, and morbidly obese children as compared to normal children.[16]

We also looked at correlation between pulmonary functions and various factors such as BMI, weight, height, and WHR. There was a significant negative correlation between the FEV1 (%) and FVC (%) with that of BMI and WHR in contrast to a previously published study, which noted a positive correlation between BMI and pulmonary function test.[19] Our results are in accordance with studies where BMI and WHR are negatively correlated to pulmonary function test.[24] Yet another study had reported a significant (or almost significant) inverse correlation with residual FVC, FEV0.75, and FEV1 among boys with over-weight and obesity.[16] BMI also showed inverse correlations with residual FVC and FEV1, both of which were border-line significant. WHR was concluded as the best predictor of residual FVC, FEV0.75, and FEV1 in the over-weight or obese group in the same study.[25]

The strength of the present study is that children with over-weight/obesity were age-matched prospectively with the control group, thus preventing any bias arising from a retrospective design. However, the limitation includes a small sample size and a higher number of boys in the obesity/over-weight group as compared to girls.

Conclusions

Pulmonary functions (FEV1, FVC) decline with an increase in BMI and WHR, although not significantly. FEV1 (%) and FVC (%) decrease significantly with an increase in BMI. Although BMI and WHR have a negative correlation with pulmonary functions, they are statistically insignificant. Height and weight have a positive correlation with pulmonary functions, which is significant.

Summary

Pulmonary functions (FEV1, FVC) decline with an increase in BMI and WHR.

FEV1 (%) and FVC (%) decrease significantly with an increase in BMI.

BMI and WHR have negative correlation with PFT, but they are statistically insignificant.

Height and weight have a positive correlation with pulmonary functions, which is significant.

We have used healthy controls for comparing PFT, which have not been used previously in most of the studies.

Take home message

BMI and WHR adversely affect the pulmonary function in children.

% FEV1 and FVC decrease with an increase in BMI. Hence, the results of pulmonary function test used for evaluation of children with asthma should be carefully interpreted.

As there is increasing prevalence of both obesity and asthma in children, primary physicians should be aware of these adverse affects of obesity of pulmonary functions.

Financial support and sponsorship

Funded by AIIMS Bhubaneswar Intramural Research Grant.

Conflicts of interest

There are no conflicts of interest.