Serum selenium and non-alcoholic fatty liver disease (NAFLD) in US adults: National Health and Nutrition Examination Survey (NHANES) 2011-2016

Background: Selenium is an essential trace element that shows beneficial or adverse health effects depending on the dose. Laboratory studies suggest that high selenium may contribute to the development of non-alcoholic fatty liver disease (NAFLD). However, human evidence is limited. We evaluated the associations of serum selenium level with serum alanine aminotransferase (ALT) activity and suspected NAFLD prevalence in U.S. adults. Methods: We conducted the cross-sectional analysis in 3827 adults aged 20 years and older without viral hepatitis, hemochromatosis, or alcoholic liver disease who participated in the National Health and Nutrition Examination Survey (NHANES) 2011-2012, 2013-2014, and 2015-2016. Serum selenium was measured using inductively coupled plasma dynamic reaction cell mass spectrometry. Suspected NAFLD cases were defined in the presence of serum ALT >30 international units (IU)/L in men and >19 I.U./L in women in the absence of other identifiable causes of liver disease. Results: The median (interquartile range) of serum selenium level was 127.9 (117.9, 139.4) mu g/L. Non-linear associations of serum selenium with NAFLD prevalence and serum ALT activity were observed in the generalized additive models with penalized splines. After adjustment for sociodemographic variables, lifestyle factors, body mass index, and NHANES survey cycles, positive associations were found at > -130 mu g/L serum selenium with both NAFLD and ALT, whereas the associations were flattened at < -130 mu g/L. Conclusions: Our findings provide evidence of non-linear associations of serum selenium with ALT activity and NAFLD prevalence. In particular, positive associations were found above serum selenium level of 130 mu g/L, whereas no association was observed below this value. This finding requires confirmation in future prospective cohort studies.