(Plos one)PONE-D-24-45392_database set.xlsx

Iodine is an essential micronutrient for the synthesis of thyroid hormones. Koreans have a tradition of consuming seaweed soup during the postpartum period, leading to a rapid increase in iodine intake in lactating women. Concerns have been raised over the large consumption of seaweed, resulting in excessive iodine intake. However, there have not been enough studies to determine the effect of excessive iodine intake through seaweed on the thyroid hormone functions of lactating women. This study used a prospective cohort of Korean postpartum women to investigate the relationship between iodine derived from seaweed intake and thyroid hormone. This study recruited 147 postpartum women within two weeks after childbirth, and 81 participated again in the follow-up study after one year. At the time of initial recruitment, dietary records including seaweed soup during the postpartum period (8 weeks), thyroid hormone levels, urinary iodine concentration (UIC), and infant growth indicators, were evaluated. In the one-year follow-up, it was evaluated in the same way. Fisher’s exact test was used to test the relationship between iodine intake during the postpartum period and thyroid hormones. The ratio of participants whose thyroid hormones (T3, FT4, and TSH) were out of the normal range was calculated for each quartile group according to iodine intake for the postpartum period and showed no significant difference between the four groups [T3: P = 0.2181; FT4: P = 0.1591; TSH; P =0.3251]. This relationship was also observed after one year [T3: P = 0.9721; FT4: P = 0.0589; TSH; P =0.7476]. Dietary iodine intake during the postpartum period and one year after had no relationship with thyroid hormone functions. Our findings suggested that a temporary increase in iodine intake during the postpartum period had no relationship with thyroid hormone functions. To confirm the results of this study further, a large follow-up study targeting postpartum women will be necessary.