Iodine supplementation: is there a need?

Association of congenital iodine deficiency syndrome and differentiated thyroid cancer: a Mendelian randomization study

BACKGROUND

The effect of iodine deficiency, especially during the fetal period, on thyroid cancer risk remains unclear. The evidence from observational studies is controversial because of the inevitable confounding factors. We studied the causal effect of congenital iodine deficiency on differentiated thyroid cancer (DTC) based on Mendelian randomization (MR).

METHODS

Two-Sample MR analysis was performed using data from published genome-wide association studies, including congenital iodine deficiency syndrome (CIDS) (353 cases, 187,684 controls) and DTC (649 cases, 431 controls) data.

RESULTS

There was a causal relationship between CIDS and DTC (P < 0.05), with CIDS increasing the DTC risk by 37.4% (OR = 1.374, 95%CI = 1.110-1.700). Heterogeneity tests and tests of multiple validities indicated that the results were solid and reliable (all P < 0.05).

CONCLUSIONS

Fetal iodine deficiency increases the risk of DTC, so future clinical studies should focus on the effect of iodine supplementation during pregnancy to reduce the risk of thyroid cancer in the offspring.

Iodine Requirements in Pediatrics: From Fetal Life to Adolescence

The aim of this mini-review is to present the current knowledge on iodine requirements in developmental age, from conception to adolescence. It is based on the analysis of updated national and international guidelines on iodine intake and the prevention of iodine deficiency. Health policy initiatives carried out in industrialized countries in previous decades have led to a dramatic improvement in nutritional iodine status in the general population. However, the prevention of iodine deficit continues to be a concern, especially for vulnerable categories, like adolescents and pregnant women.

Iodine Nutrition and Iodine Supplement Initiation in Association with Thyroid Function in Mildly-to-Moderately Iodine-Deficient Pregnant and Postpartum Women

BACKGROUND

Whereas the adverse effects of severe iodine deficiency during pregnancy are well documented, the effects of mild-to-moderate deficiency are not well established.

OBJECTIVES

We aimed to explore whether iodine nutrition and timing of iodine supplement initiation are associated with thyroid function in pregnant and postpartum women.

METHODS

In this cohort study, 137 pregnant women were enrolled and followed up at gestational weeks (GWs) 18 and 36, and 3 and 6 mo postpartum. Thyroid function tests [thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), and free thyroxine (fT4)], urinary iodine and creatinine concentration (UIC:Cr), and iodine intake (including iodine supplement use) were measured at each time point. The associations between thyroid hormone concentrations and UIC:Cr, iodine intakes, and iodine supplement use were estimated using multiple generalized estimating equation models.

RESULTS

The median UIC at GW18 was 94 μg/L, indicating mild-to-moderate iodine deficiency. UIC:Cr (β; 95% CI) per 100 μg/g was negatively associated with fT3 (-0.191; -0.331, -0.051) and fT4 (-0.756; -1.372, -0.141) concentrations. Iodine intake (β; 95% CI) per 100 μg/d was positively associated with TSH (0.099; 0.022, 0.177), and negatively associated with fT3 (-0.084; -0.0141, -0.027) and fT4 (-0.390; -0.599, -0.182) concentrations. Compared with no use of supplement, those initiating an iodine-containing supplement prepregnancy and continuing through pregnancy had lower TSH (estimated means) (1.35 compared with 1.68 mIU/L, P = 0.021), and higher fT3 (4.48 compared with 4.28 pmol/L, P = 0.035) and fT4 (15.2 compared with 14.4 pmol/L, P = 0.024) concentrations.

CONCLUSIONS

Lower iodine availability during pregnancy and postpartum was associated with lower TSH, and higher fT3 and fT4 concentrations. The use of an iodine-containing supplement that was initiated prepregnancy and continuing through pregnancy was associated with lower TSH, and higher fT3 and fT4 concentrations, which may suggest improved thyroid function. These findings support the notion that optimization of iodine intake should start before pregnancy.This trial was registered at clinicaltrials.gov as NCT02610959.