Higher toenail selenium is associated with increased insulin resistance risk in omnivores, but not in vegetarians

Background The relationship between selenium (Se) and insulin resistance remains unclear. We aim to explore the association between toenail Se levels and insulin resistance through a cross-sectional study comprising Chinese vegetarians and matched omnivores. Methods In this study, we enrolled 220 vegetarians and 220 omnivores matched by age and sex from Shanghai. The inductively coupled plasma mass spectrometry method was used to measure toenail Se levels. Dietary Se intakes were assessed by the 24-h dietary recall method. Blood samples were collected to measure fasting blood glucose level and fasting insulin concentrations. Insulin resistance index (HOMA-IR) and insulin secretion index (HOMA-B) were calculated to evaluate insulin resistance. Multi-linear regression analysis was performed to determine the association between toenail Se levels and insulin resistance, after adjusting for confounders. Results The mean ages of vegetarians (76 vegans, 144 lacto-ovo-vegetarians) and omnivores were 35.96 ± 8.73 years and 35.23 ± 8.93 years, respectively. Of these, 180 (81.8%) were female and 40 (18.2%) were male. No association was found between toenail Se levels and insulin resistance in vegetarians. However, the concentration of Se in toenails was positively correlated with fasting insulin levels ( β = 1.030, 95% CI : 0.393 to 1.667) and HOMA-IR ( β = 0.245, 95% CI : 0.098 to 0.392) in omnivores, after multivariate adjustment for age, sex, BMI, alcohol consumption, income, and daily dietary intakes (energy, protein, fat, carbohydrate, and fiber). This positive relationship persisted only in omnivores whose dietary Se intake was above 60 μg/d. Conclusions Higher toenail Se levels were associated with increased insulin resistance risk in Chinese omnivores whose dietary Se intake was above 60 μg/d, but not in vegetarians. These findings create awareness on the association of dietary Se intake above 60 μg/d with the risk of insulin resistance.