Low maternal iodine intake and subsequent risk of pharmacologically treated hypertension: A population-based prospective cohort study.

Background & Aims: Iodine deficiency is linked to multiple adverse health outcomes, but there is scarce knowledge regarding iodine intake and development of chronic hypertension. We aimed to investigate the prospective association between habitual dietary iodine intake and pharmacologically treated hypertension in mothers up to 10 years after delivery.

Methods: The present study is based on data from an ongoing pregnancy cohort and includes 58,629 women without thyroid dysfunction and hypertension at baseline. The study outcome was new-onset hypertension defined according to antihypertensive medication use initiated 90 days after delivery registered in the national prescription database. We estimated hazard ratios (HR) with 95 % Confidence Intervals (95 % CI) using Cox regression models.

Results: During a median follow-up duration of 7.1 years, a total of 1422 (2.4 %) women developed new-onset hypertension. There was a non-linear association between dietary iodine intake and new-onset hypertension. Women with iodine intakes lower than 100 μg/day had significantly higher risk than those with iodine intakes in the recommended range 150-199 μg/day (adjusted HR, 1.29; 95 % CI: 1.09, 1.53). This was evident in normotensive pregnancies (adjusted HR 1.25; 95 % CI: 1.01, 1.54) and in women with gestational hypertension (adjusted HR 1.35; 95 % CI: 1.00, 1.83). The association between low iodine intake and hypertension remained in all sensitivity analyses considering pre-pregnancy and pregnancy-related factors.

Conclusions: This study suggests that women with iodine intakes below 100 μg/day have a higher likelihood of new-onset hypertension and adds supporting evidence to the importance of correcting mild-to-moderate iodine deficiency in women of reproductive age.