Iodine intake in the Swiss population 100years after the introduction of iodised salt: a cross-sectional national study in children and pregnant women.

Abstract

The Swiss voluntary salt iodisation programme has successfully prevented iodine deficiency for 100years, but dietary habits are changing and todayonly one-third of processed foods contain iodised salt. We aimed to monitor the current iodine status in childrenand pregnant women. We conducted a nationwide cross-sectional study in children (6-12years) and pregnant women and measured the urinary iodine concentration (UIC) in spot urine samples. We estimated the iodine intake using UIC and urinary creatinine concentration (UCC) and determined the prevalence of intakes below the average requirement (AR) using the SPADE method. We measured dried blood spot (DBS) thyroglobulin (Tg), TSH and total T4 in pregnant women. The median UIC was 127μg/L (bootstrapped 95% CI 119, 140, n = 362) in children and 97μg/L (bootstrapped 95% CI 90, 106, n = 473) in pregnant women. The estimated prevalence of inadequate iodine intake (< 65μg/day) was 5.4% (bootstrapped 95% CI 0.0, 14.6) in children. Half (47%) of the women consumed iodine-containing multivitamin and mineral supplements (≥ 150μg/day). Compared to non-users, users had higher median UIC (129 vs. 81μg/L, P < 0.001), lower prevalence of inadequacy (< 160μg/day; 0.2 vs. 31%) and lower DBS-Tg (23 vs. 29μg/L, P < 0.001). All women were euthyroid. The Swiss diet and current salt fortification provides adequate iodine intake in children, but not in all pregnant women. Iodine supplements cover the dietary gap in pregnancy but are not universally consumed. Therefore, improved use of iodised salt in processed foods is desired to ensure adequate iodine intake in all population groups. This trial was registered at clinicaltrials.gov as NCT04524013.