The effect of vitamin D and frailty on mortality among non-institutionalized US older adults

BACKGROUND/OBJECTIVES: Although both frailty and low vitamin D have been separately associated with an increased risk for adverse health, their joined effects on mortality have not been reported. The current study examined prospectively the effects of frailty and vitamin D status on mortality in US older adults. SUBJECTS/METHODS: Participants aged >= 60 years in The Third National Health and Nutrition Examination Survey with 12 years of mortality follow-up were included in the analysis (n = 4731). Frailty was defined as meeting three or more criteria and pre-frailty as meeting one or two of the five frailty criteria (low body mass index (BMI), slow walking, weakness, exhaustion and low physical activity). Vitamin D status was assessed by serum 25-hydroxyvitamin D (25(OH) D) and categorized into quartiles. Analyses were adjusted for gender, race, age, smoking, education, latitude and other comorbid conditions. RESULTS: Serum 25(OH) D concentrations were lowest in participants with frailty, intermediate in participants with pre-frailty and highest in participants without frailty. The odds of frailty in the lowest quartile of serum 25(OH) D was 1.94 times the odds in the highest quartile (95% confidence interval (CI): 1.09-3.44). Mortality was positively associated with frailty, with the risk among participants who were frail and had low serum 25(OH) D being significantly higher than those who were not frail and who had high concentrations of serum 25(OH) D (hazards ratio 2.98; 95% CI: 2.01-4.42). CONCLUSION: Our results suggest that low serum 25(OH) D is associated with frailty, and there is additive joint effects of serum 25(OH) D and frailty on all-cause mortality in older adults.