Urinary Lignan Levels and Thyroid Function in Adults from NHANES 2007-2010

Abstract

Background: Enterodiol and enterolactone are lignans, a group of phytoestrogens produced by bacteria in the colon that act on plant precursors. Flaxseed is the largest dietary source of lignans, but are also found in other seeds, grains, fruits, and vegetables. Health effects research on enterodiol and enterolactone is limited. However, some studies find associations between high dietary lignan exposure and reduced risk of thyroid and breast cancer and cardiovascular disease.Method: We performed a cross-sectional analysis examining the relation between urinary lignan concentrations and serum of thyroid levels in adults free of thyroid disease in the National Health and Nutrition Examination Survey (2007-2010). Specifically, we conducted multivariable analyses relating the concentrations of each urinary lignan (enterodiol, enterolactone) to serum concentrations of thyroid stimulating hormone [TSH], free triiodothyronine [T3], total T3, free thyroxine [T4], total T4, thyroperoxidase [TPO] antibodies, adjusting for sociodemographics, creatinine, iodine and thiocyanate.Results: In women, enterodiol and enterolactone were inversely associated with total T4. A 10-fold increase in enterodiol was associated with a 1.8% decrease (95% CI: -2.8%, -0.89%) in total T4, and a 10-fold increase in enterolactone was associated with a 1.6% decrease (95% CI: -2.5%, -0.68%) in total T4. Among men, a 10-fold increase in enterolactone was associated with a 1.0% increase (95% CI: -2.32%, 0.23%) in total T4 and a 10-fold increase in enterodiol was associated with a 2.1% decrease (95% CI: -3.4%, -0.82%) in total T4. In addition, among women, there was an inverse association between enterolactone and free T3, where a 10-fold increase in enterolactone was associated with a 1.6% decrease (95% CI: -2.5%, -0.68%) in free T3.Conclusion: In the present study, urinary lignan concentrations were associated with serum concentrations of selected thyroid hormones in a sex-dependent fashion.