A U-shaped association between selenium intake and cancer risk

While selenium is a cofactor of several antioxidant enzymes against cancer and is essential for human health, its excess intake may also be harmful. Though a safe intake of selenium has recently been recommended, it is not well understood in the Asian population. We aimed to determine the association between dietary intake of selenium and cancer risk in a case-control study of 3758 incident cancer cases (i.e., stomach, colon, rectum, lung cancers, and other sites) and 2929 control subjects in Vietnam. Daily intake of selenium was derived from a semiquantitative food frequency questionnaire. The unconditional logistic regression model was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) for the association between selenium intake and cancer risk. We observed a U-shaped association between selenium intake and cancer risk. A safe intake ranged from 110.8 to 124.4 µg/day (mean 117.8 µg/day). Compared to individuals with the safe intake of selenium, individuals with the lowest intake (i.e., 27.8-77.2 µg/day) were associated with an increased risk of cancer (OR = 3.78, 95% CI 2.89-4.95) and those with the highest intake (169.1-331.7 µg/day) also had an increased cancer risk (OR = 1.86, 95% CI 1.45-2.39). A U-shaped pattern of association between selenium intake and cancer risk was stronger among participants with body mass index (BMI) < 23 kg/m² and never smokers than BMI ≥ 23 kg/m² and ever smokers (P's_{heterogeneity} = 0.003 and 0.021, respectively) but found in both never and ever-drinkers of alcohol (P_{heterogeneity} = 0.001). A U-shaped association between selenium intake and cancer risk was seen in cancer sites of the stomach, colon, rectum, and lung cancers. In summary, we found a U-shaped association between selenium intake and cancer risk and a safe selenium intake (mean: 117.8 µg/day) in the Vietnamese population. Further mechanistic investigation is warranted to understand better a U-shaped association between selenium intake and cancer risk.