Is there an increased risk of iodine deficiency among reproductive‐age women (18–45) with “normal” thyroid function?
Authors: Panth Pallavi , DiMarco Nancy M , Petterborg Larry J 
Published: November 2023

Decreasing iodine intake in recent US diets may predispose reproductive‐age women to iodine deficiency disorders and thyroid dysfunction.

Purpose

to investigate efficacy of iodine supplementation in 18–45 year old women diagnosed with iodine deficiency in improving overall iodine nutrition status, thyroid function, and body composition during a 6‐month randomized, double‐blind placebo‐controlled trial.

Study

non‐pregnant women without a history of thyroid disease, with normal serum thyroid stimulating hormone (TSH), mean=1.57 μU/mL, and negative for thyroid peroxidase antibody (TPOAb), were randomized into two groups: iodine (IG, n=65, Iodoral® 12.5 mg iodine) or placebo (PG, n=38, glucose tablet). All participants also received a generic multi‐vitamin‐mineral supplement to provide the recommended daily allowance(RDA) for iodine (150 μg/day). Assessments included iodine status determination (24‐hr urine iodine (UI), % iodine saturation (%IS), sodium iodide symporter (NIS) ratio), body composition analysis (body mass index (BMI), % body fat, fat mass, lean mass, visceral abdominal fat mass (VAT), and bone mineral density (BMD) using Dual Energy X‐ray Absorptiometry‐DXA), resting metabolic rate (RMR), serum concentrations of free thyroxine (T4), free tri‐iodithyronine (T3), thyroid stimulating hormone (TSH), thyroglobulin antibody (Tg) and thyroid‐peroxidase antibody (TPOab). Participants also completed 3‐day diet records, health history questionnaires and physical activity questionnaires. Compliance was assessed by pill‐count.

Results

More than 90% of participants reported reduced salt intake in their diets, documented no knowledge of dietary sources of iodine, and did not know difference between iodized vs. regular table salt. Median consumption of dietary iodine was less than 100 μg/day which was significantly lower than 150 μg/day RDA for iodine in the general population and 250 μg/day RDA in pregnant and lactating women. Baseline data (N=108) showed mean UI of 35.52mg/24hr vs >44 mg/24hr, mean % IS 70.93% vs >90%, and mean NIS ratio 27.86 vs 28–74, between study population and expected mean, respectively, indicating iodine deficiency. Of those completing study (n=64; IG, n=32, PG, n=32), 24‐hr UI increased from 34.9 to 38.1 mg/24hr, % IS increased from 69.8 to 76.3%, and RMR increased from 1586 to 1628 Kcals. Between the groups (n=32, IG, n=32, PG), UI increased from 35.8 to 39.6 mg/24hr in IG vs 34.0 to 36.6 mg/24hr in PG, % IS increased from 71.6 to 79.3% in IG vs 67.9 to 73.2 in PG, and RMR increased from 1600 to 1650 Kcals in IG (n=32) vs 1572–1607 Kcals in PG. NIS ratio and % body fat were not significantly changed between the groups. Iodine supplementation may improve overall iodine nutrition status in populations similar to the study population of reproductive‐age women who are especially vulnerable to the detrimental maternal and fetal effects of iodine deficiency.

Support or Funding Information

Funded by Human Nutrition Research Funds, Texas Woman's University Research Enhancement Grant, and Optimox Corporation.