Being mildly deficient in iodine can lengthen the time to conception and the probability of conceiving, finds a study from China published in Nutrients. The study indicates the importance of maintaining a good iodine intake in all women of reproductive age, say the study authors. The findings support those of a previous study in 2018 that found moderate to severe iodine deficiency increased time to conception in a cohort of US women.
It has long been known that iodine is critical in pregnancy for healthy development of the fetus. But the authors of this study say impacts on fertility have been overlooked, especially for mild deficiency.
Iodising salt is a cheap and effective way of reducing iodine deficiency. Historically many people in China were at risk of iodine deficiency. To address this the country introduced a iodised salt campaign in 1995 and eliminated iodine deficiency by 2000. However, the monopoly on salt ceased in 2016 amongst concerns about thyroid disease, according to the study authors, with the result that non-iodised salt became more available. They report that the percent of households consuming iodised salt has dropped from 95% to 80% and average (median) iodine levels in pregnant women have dropped to a level that is mildly insufficient at 130.47 micrograms/L.
The researchers gathered data on urinary iodine in pregnant women between 2015 and 2017 and carried out a cross-sectional retrospective study of pregnant women in Zhejiang province in 2018 including women from the coastal and inland provinces. The women provided urine samples and samples of their usual salt supply. They were interviewed about their reproductive history.
The women from the coast had low iodine levels indicating a mild deficiency (median concentration in urine of 119.6 microg/L) while those from inland had higher levels (median concentration of 147.1 microg/L) and were iodine sufficient.
The median time to pregnancy was 5 months in the deficient women compared with 4 months in iodine sufficient women, but this wasn’t a significant difference (P=0.266). However, the percent of women that failed to get pregnant after 13 months of trying was significantly higher amongst deficient women compared with iodine sufficient women – 20% vs 14%. After adjusting for confounding variables, the researchers still saw a significant decrease in ability to conceive in iodine deficient women.
The researchers concluded: “These findings indicate the importance of ongoing monitoring of iodine nutrition in women of reproductive age. Keeping a safe and optimal level of iodine nutrition during pregnancy should be emphasized.”
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Xing, Mingluan, Simeng Gu, Xiaofeng Wang, Guangming Mao, Zhe Mo, Xiaoming Lou, Xueqing Li, Xuemin Huang, Yuanyang Wang, and Zhifang Wang. 2021. "Low Iodine Intake May Decrease Women’s Fecundity: A Population-Based Cross-Sectional Study" Nutrients 13, no. 9: 3056. https://doi.org/10.3390/nu13093056