The relationship between iodine nutrition and thyroid disease in lactating women with different iodine intakes

Abstract

Areas with low, adequate and excessive I content in water co-exist in China. Limited data are currently available on I nutrition and thyroid disease in lactating women and their breast-fed infants with different I intakes. This study aimed to evaluate I nutrition in both lactating women and their infants and the prevalence of thyroid disease in areas with different levels of I in water. From January to June 2014, a total of 343 healthy lactating women (excluding those taking anti-thyroid drugs or I supplements within a year of the study, consuming seafood at the time of the study or those diagnosed with congenital thyroid disease) from Beihai in Guangxi province and Jiajiazhuang, Yangcheng, Jicun and Pingyao townships in Shanxi province were selected. Compared with the I-sufficient group, median urinary I concentrations in both lactating women and infants as well as breast milk I levels were significantly lower in the I-deficient group (P < 0·001). The prevalence of thyroid disease in lactating women, particularly subclinical hypothyroidism, was higher in the I-excess group than in the I-sufficient group (P < 0·05). In areas with excessive water I content, high thyroid peroxidase antibody and high thyroglobulin levels were risk factors for abnormal thyroid-stimulating hormone levels. Our data collectively suggest that excessive I intake potentially causes subclinical hypothyroidism in lactating women. Moreover, enhanced monitoring of I status is important to avoid adverse effects of I deficiency or excess, particularly in susceptible populations such as pregnant or lactating women and infants.

Activation of the Nrf2-Keap 1 Pathway in Short-Term Iodide Excess in Thyroid in Rats

“…Paul et al demonstrated that when normal volunteers received 1500  μ g of supplemental iodine daily for 14 days, a small decrease in serum T3 and T4 concentrations with compensatory increase of TSH was detected, although all values remained within the normal ranges [34]. However, the presence of handicaps such as an increased autoimmune susceptibility, fetal period, extremes of age, pregnancy, lactation, or an active pathological entity significantly impair these mechanisms [1, 35–37]. …”

Excess iodine intake: sources, assessment, and effects on thyroid function

“…Iodine is a critical micronutrient during the first 1000 days of life . Iodine in breast milk is highly variable depending upon maternal iodine intake . In iodine‐sufficient populations, if iodine intake is borderline, iodine is preferentially partitioned into breast milk to safeguard infant requirements .…”

“…In iodine‐sufficient populations, if iodine intake is borderline, iodine is preferentially partitioned into breast milk to safeguard infant requirements . High breast milk iodine concentration (BMIC) is reported in areas with excess iodine intakes . Whether there is an active downregulation of iodine secretion into breast milk at elevated maternal iodine intakes remains unclear.…”

“…Breast milk is the principal route to assure infant iodine intakes in both exclusively breastfed infants and those also receiving complementary foods (see above). Mothers with excessive iodine intake typically have a high BMIC . Excess iodine consumption during lactation may not only increase the maternal susceptibility to thyroid dysfunction, but case reports also suggest the risk of subclinical and clinical hypothyroidism in their infants induced by excess BMICs .…”

“…3,4,15,[44][45][46] Iodine in breast milk is highly variable depending upon maternal iodine intake. 47,48 In iodine-sufficient populations, if iodine intake is borderline, iodine is preferentially partitioned into breast milk to safeguard infant requirements. 47 High breast milk iodine concentration (BMIC) is reported in areas with excess iodine intakes.…”