The present invention addresses the problem of examining the physiological activity of selenoneine which is an organic selenium compound and thus finding novel uses thereof. To solve this problem, provided are a composition comprising an organic selenium compound as an active ingredient, and a food, food composition and medicinal composition each comprising the aforesaid composition. Intake of the composition, etc. according to the present invention is expected to result in remarkable effects of reducing oxidative stress, suppressing lipid oxides, preventing ischemic diseases, ameliorating metabolic syndrome, ameliorating abnormal glucose tolerance, preventing and ameliorating disorders including lipid metabolism disorder accompanied by metabolic syndrome, inhibiting cancer, inhibiting systemic immunosuppression, inhibiting vascular endothelial disorders, inhibiting arteriosclerosis, preventing dementia, improving brain functions, protecting corneal epithelial cells, ameliorating dry eye or suppressing inflam
