Plasma 25-hydroxyvitamin D concentrations, vitamin D deficiency, and mortality in community-dwelling Japanese adults.

Blood 25-hydroxyvitamin D (25(OH)D) concentrations vary considerably by season and sex. The present study aimed to determine associations between vitamin D deficiency and mortality in Japanese adults and identify risk thresholds according to 25(OH)D concentrations. This was a cohort study with an 11-year follow-up. Participants were 8,285 community-dwelling Japanese adults aged 40 to 74 years. Plasma 25(OH)D concentrations were measured by chemiluminescent immunoassay at baseline, and divided into quintiles for each of the subgroups stratified by season and sex (denoted as season- and sex-stratified quintiles). The main outcome was all-cause mortality. Hazard ratios (HRs) were calculated using a Cox proportional hazards model. Mean age and 25(OH)D concentration were 59.9 years (SD=9.1) and 50.1 nmol/L (SD=18.1), respectively. Lower season- and sex-stratified quintiles were associated with higher hazards of all-cause mortality (P for trend=0.0015), with the first quintile (median=28.2 nmol/L) having a higher HR (HR=1.46, 95% CI, 1.13-1.88) than the highest quintile (reference). When crude quintiles were used, the overall association was similar (P for trend=0.0027), with the first (median=28.0 nmol/L) and second (median=39.7 nmol/L) quintiles having higher HRs (HR=1.40, 95% CI, 1.06-1.85 and 1.38, 95% CI, 1.07-1.77, respectively) than the reference. The risk threshold difference was estimated to be approximately 10 nmol/L. In conclusion, low blood 25(OH)D concentrations are associated with high mortality risk. Crude blood 25(OH)D concentration may modulate the estimated risk threshold for vitamin D deficiency associated with mortality.