Kosuke Inoue1,2, Angela M Leung3,4, Takehiro Sugiyama5,6, Tetsuro Tsujimoto7, Noriko Makita2, Masaomi Nangaku2, Beate R Ritz1. 1. 1 Department of Epidemiology, UCLA Fielding School of Public Health , Los Angeles, California. 2. 2 Division of Nephrology and Endocrinology, University of Tokyo Graduate School of Medicine , Tokyo, Japan . 3. 3 Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, UCLA David Geffen School of Medicine , Los Angeles, California. 4. 4 Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, VA Greater Los Angeles Healthcare System , Los Angeles, California. 5. 5 Diabetes and Metabolism Information Center, Research Institute , National Center for Global Health and Medicine, Tokyo, Japan . 6. 6 Department of Public Health/Health Policy, University of Tokyo , Tokyo, Japan . 7. 7 Department of Diabetes, Endocrinology, and Metabolism, Center Hospital, National Center for Global Health and Medicine , Tokyo, Japan .
Abstract
BACKGROUND: Iodine deficiency has long been recognized as an important public health problem. Global approaches such as salt iodization that aim to overcome iodine deficiency have been successful. Meanwhile, they have led to excessive iodine consumption in some populations, thereby increasing the risks of iodine-induced thyroid dysfunction, as well as the comorbidities and mortality associated with hypothyroidism and hyperthyroidism. This study aimed to elucidate whether iodine intake is associated with mortality among U.S. adults. METHODS: This was an observational study to estimate mortality risks according to urinary iodine concentration (UIC) utilizing a nationally representative sample of 12,264 adults aged 20-80 years enrolled in the National Health and Nutrition Examination Survey (NHANES) III. Crude and multivariable Cox proportional hazards regression models were employed to investigate the association between UIC (<50, 50-99, 100-299, 300-399, and ≥400 μg/L) and mortalities (all-cause, cardiovascular, and cancer). In sensitivity analyses, the study adjusted for total sodium intake and fat/calorie ratio in addition to other potential confounders. Stratum-specific analyses were also conducted to estimate the effects of UIC on mortality according to age, sex, race/ethnicity, and estimated glomerular filtration rate category. RESULTS: Over a median follow-up of 19.2 years, there were 3159 deaths from all causes. Participants with excess iodine exposure (UIC ≥400 μg/L) were at higher risk for all-cause mortality compared to those with adequate iodine nutrition (hazard ratio = 1.19 [confidence interval 1.04-1.37]). Elevated hazard ratios of cardiovascular and cancer mortality were also found, but the confidence interval of the effect estimates included the null value for both outcomes. Low UIC was not associated with increased mortality. Restricted cubic spline models showed similar results for all outcomes. The results did not change substantially after adjusting for total sodium intake and fat/calorie ratio. None of the potential interactions were statistically significant on a multiplicative scale. CONCLUSION: Higher all-cause mortality among those with excess iodine intake compared to individuals with adequate iodine intake highlights the importance of monitoring population iodine status. Further studies with longitudinal measures of iodine status are needed to validate these results and to assess the potential risks excess iodine intake may have on long-term health outcomes.
BACKGROUND:Iodinedeficiency has long been recognized as an important public health problem. Global approaches such as salt iodization that aim to overcome iodinedeficiency have been successful. Meanwhile, they have led to excessive iodine consumption in some populations, thereby increasing the risks of iodine-induced thyroid dysfunction, as well as the comorbidities and mortality associated with hypothyroidism and hyperthyroidism. This study aimed to elucidate whether iodine intake is associated with mortality among U.S. adults. METHODS: This was an observational study to estimate mortality risks according to urinary iodine concentration (UIC) utilizing a nationally representative sample of 12,264 adults aged 20-80 years enrolled in the National Health and Nutrition Examination Survey (NHANES) III. Crude and multivariable Cox proportional hazards regression models were employed to investigate the association between UIC (<50, 50-99, 100-299, 300-399, and ≥400 μg/L) and mortalities (all-cause, cardiovascular, and cancer). In sensitivity analyses, the study adjusted for total sodium intake and fat/calorie ratio in addition to other potential confounders. Stratum-specific analyses were also conducted to estimate the effects of UIC on mortality according to age, sex, race/ethnicity, and estimated glomerular filtration rate category. RESULTS: Over a median follow-up of 19.2 years, there were 3159 deaths from all causes. Participants with excess iodine exposure (UIC ≥400 μg/L) were at higher risk for all-cause mortality compared to those with adequate iodine nutrition (hazard ratio = 1.19 [confidence interval 1.04-1.37]). Elevated hazard ratios of cardiovascular and cancer mortality were also found, but the confidence interval of the effect estimates included the null value for both outcomes. Low UIC was not associated with increased mortality. Restricted cubic spline models showed similar results for all outcomes. The results did not change substantially after adjusting for total sodium intake and fat/calorie ratio. None of the potential interactions were statistically significant on a multiplicative scale. CONCLUSION: Higher all-cause mortality among those with excess iodine intake compared to individuals with adequate iodine intake highlights the importance of monitoring population iodine status. Further studies with longitudinal measures of iodine status are needed to validate these results and to assess the potential risks excess iodine intake may have on long-term health outcomes.
Authors: Nicolas Rodondi; Wendy P J den Elzen; Douglas C Bauer; Anne R Cappola; Salman Razvi; John P Walsh; Bjørn O Asvold; Giorgio Iervasi; Misa Imaizumi; Tinh-Hai Collet; Alexandra Bremner; Patrick Maisonneuve; José A Sgarbi; Kay-Tee Khaw; Mark P J Vanderpump; Anne B Newman; Jacques Cornuz; Jayne A Franklyn; Rudi G J Westendorp; Eric Vittinghoff; Jacobijn Gussekloo Journal: JAMA Date: 2010-09-22 Impact factor: 56.272
Authors: J G Hollowell; N W Staehling; W H Hannon; D W Flanders; E W Gunter; G F Maberly; L E Braverman; S Pino; D T Miller; P L Garbe; D M DeLozier; R J Jackson Journal: J Clin Endocrinol Metab Date: 1998-10 Impact factor: 5.958