Sex differences in the association between thyroid-stimulating hormone levels and depressive symptoms among the general population with normal free T4 levels

Background: : Overt and subclinical thyroid dysfunction has been reported to be related to depression. Thyroid diseases have been known to occur more frequently in women. However, scarce data are available on effects and sex differences of changes in thyroid-stimulating hormone (TSH) levels, with a normal range of thyroid hormones, on depression. This study aimed to investigate the association between TSH levels and depressive symptoms, according to sex, in individuals from the general population with free thyroxine (fT4) values within the normal range. Methods: : Data from the 2014 Korea National Health and Nutritional Examination Survey were used for this study. The study population of 1651 Korean adults was categorized by tertiles of TSH levels. The presence of depressive symptoms was determined using a cut-off score of 5 in the Patient Health Questionnaire-9. Results: : The highest TSH tertile group was 1.92 times more likely to have depressive symptoms in men after adjustment for covariates than the lowest TSH tertile (adjusted odds ratio: 1.92, 95% confidence interval: 1.11–3.31, P = 0.019). Contrastingly, the highest TSH tertile was associated with an approximately 35% lower prevalence of depressive symptoms in women (adjusted odds ratio: 0.65, 95% confidence interval: 0.43–0.97, P = 0.034). Limitations: : Cross-sectional design and unrecognized confounding factors, are the main limitations of our study. Conclusions: : Sex may play a substantial role in the relationship between TSH and depressive symptoms. Sex differences might be associated with differences in thyroid response, TSH blunting, thyroid autoimmunity, and sex hormone levels.