Although vitamin deficiency has become rare in the current Japan, vitamin insufficiency, milder than deficiency, is a risk of various non-communicable diseases. However, reports on the disease risk associated with vitamin insufficiency are scarce in Japan, which has led us to perform a series of studies on the clinical aspects of vitamins, as below. In the institutionalized elderly, vitamin D deficiency/insufficiency was found to be susceptible to upper respiratory tract infection and pneumonia. Although serum 25-hydroxyvitamin D [25(OH)D] concentration well reflects vitamin D status, its measurement requires venipuncture and special laboratory assays. Therefore, we developed a simple questionnaire for vitamin D deficiency risk without the necessity of blood testing. Since recently, the importance of vitamin D nutritional status in pregnant women and fetuses is increasingly recognized, the study is underway to construct a predictive model for serum 25(OH)D level and to develop a screening tool for predicting vitamin D deficiency risk. To elucidate the role of dietary vitamins intakes is of much significance for prevention of non-communicable diseases. Therefore, the development of tools to simply assess vitamin nutritional status and to provide specific remedies for vitamin deficiency/insufficiency risk is further needed.