Trends in the prevalence of hypovitaminosis D over a 10-year period in Japan: the research on osteoarthritis/osteoporosis against disability study 2005–2015

We examined the trends in vitamin D insufficiency and deficiency over a 10-year period in the general population. The prevalence of deficiency significantly decreased (29.5% vs. 21.6%), whereas mean serum levels increased (23.3 ng/mL vs. 25.1 ng/mL). These trends may reduce the incidence of osteoporosis and osteoporotic fractures. We aimed to clarify the trends in the prevalence of vitamin D insufficiency and deficiency in the general population using population-based cohort data from a baseline survey and a follow-up survey conducted 10 years later. A baseline survey of the Research on Osteoarthritis/Osteoporosis Against Disability (ROAD) study was conducted from 2005 to 2007. Blood samples were collected to measure serum 25-hydroxyvitamin D (25D) and intact parathyroid hormone levels from 1,683 participants (595 men, 1,088 women). Participants also completed an interviewer-administered questionnaire, and underwent bone mineral density measurements and radiographic examinations. The fourth survey was conducted from 2015 to 2016 with 1,906 individuals (637 men, 1,269 women), including both follow-up participants from the baseline survey and newly recruited individuals to increase the sample size for future longitudinal analyses. All participants completed assessments identical to those in the baseline survey. Vitamin D deficiency and insufficiency were defined as serum 25D levels of < 20 ng/mL and ≥ 20 ng/mL but < 30 ng/mL, respectively. The mean serum vitamin D levels were 23.3 ng/mL at baseline and 25.1 ng/mL at the fourth survey, indicating a significant increase (p < 0.001). The prevalences of vitamin D insufficiency and deficiency were 52.9% and 29.5%, respectively, at baseline, and 54.8% and 21.6%, respectively, in the fourth survey, indicating a significant decrease in vitamin D deficiency (p < 0.001). In this population-based survey with a 10-year interval, the prevalence of hypovitaminosis D significantly decreased. This favourable trend may contribute to future reductions in the incidence of osteoporosis and osteoporotic fractures.