Is low iodine a risk factor for cardiovascular disease in Americans without thyroid dysfunction? Findings from NHANES.

BACKGROUND AND AIMS: Low body iodine levels are associated with cardiovascular disease, in part through alterations in thyroid function. While this association suggested from animal studies, it lacks supportive evidence in humans. This study examined the association between urine iodine levels and presence of coronary artery disease (CAD) and stroke in adults without thyroid dysfunction.

METHODS AND RESULTS: This cross-sectional study included 2440 adults (representing a weighted n = 91,713,183) aged ≥40 years without thyroid dysfunction in the nationally-representative 2007-2012 National Health and Nutrition Examination Survey. The age and sex-adjusted urine iodine/creatinine ratio (aICR) was categorized into low (aICR<116 μg/day), medium (116 μg/day ≤ aICR < 370μg/day), and high (aICR ≥ 370μg/day) based on lowest/highest quintiles. Stroke and CAD were from self-reported physician diagnoses. We examined the association between low urine aICR and CAD or stroke using multivariable logistic regression modeling. The mean age of this population was 56.0 years, 47% were women, and three quarters were non-Hispanic whites. Compared with high urine iodine levels, multivariable adjusted odds ratios aOR (95% confidence intervals) for CAD were statistically significant for low, aOR = 1.97 (1.08-3.59), but not medium, aOR = 1.26 (0.75-2.13) urine iodine levels. There was no association between stroke and low, aOR = 1.12 (0.52-2.44) or medium, aOR = 1.48 (0.88-2.48) urine iodine levels.

CONCLUSION: The association between low urine iodine levels and CAD should be confirmed in a prospective study with serial measures of urine iodine. If low iodine levels precede CAD, then this potential and modifiable new CAD risk factor might have therapeutic implications.