Serum 25-hydroxyvitamin D levels and risk of all-cause and cause-specific mortality: A 14-year prospective cohort study

Abstract

Background & AimsThe circulating vitamin D level that is optimal for health is unknown. This study aimed to examine the association between circulating vitamin D level and risk of all-cause and cause-specific mortality. MethodsThis prospective cohort study included 18,797 Korean adults aged 40 years or older, living in rural areas, with no history of cancer or cardiovascular disease (CVD) at baseline. Serum 25-hydroxyvitamin D (25(OH)D) levels were measured at baseline. Participants were followed-up from the survey date (2005–2012) until December 31, 2021. Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for mortality by baseline vitamin D level. Restricted cubic splines were used to explore the nonlinearity. ResultsThe median (interquartile range) of 25(OH)D level was 55.8 (40.8–71.8) nmol/L. During a median follow-up of 14.3 years, 2,250 deaths were recorded. Compared with participants with a 25(OH)D level < 30 nmol/L, higher vitamin D levels (30 to < 50, 50 to < 75, and ≥ 75 nmol/L) were associated with a lower risk of all-cause mortality: HR (95% CI) of 0.82 (0.69–0.98), 0.74 (0.62–0.88), and 0.69 (0.57–0.84), respectively. A nonlinear relationship between vitamin D level and all-cause mortality was observed, with the risk plateauing between 50 and 60 nmol/L (p for nonlinearity = 0.009). The association was more pronounced for cancer-related mortality. HR 0.55 (95% CI: 0.39–0.77) for a 25(OH)D level ≥ 75 nmol/L compared with < 30.0 nmol/L. Low vitamin D levels were associated with increased CVD mortality in men. ConclusionsVitamin D level was inversely associated with all-cause and cause-specific mortality in middle-aged and older adults. Maintaining a serum 25(OH)D level of approximately 50–60 nmol/L may contribute to longevity and warrants further investigation.