Abstract
Serum vitamin D deficiency is widespread among older adults and is a potential modifiable risk factor for frailty. Moreover, frailty has been suggested as an intermediate step in the association between low levels of vitamin D and mortality. Hence, we conducted a systematic review of the literature and meta-analysis to test the possible association of low concentrations of serum 25-hydroxyvitamin D (25(OH)D), a marker of vitamin D status, with frailty in later life. We reviewed cross-sectional or longitudinal studies evaluating populations of older adults and identifying frailty by a currently validated scale. Meta-analyses were restricted to cross-sectional data from studies using Fried’s phenotype to identify frailty. Twenty-six studies were considered in the qualitative synthesis, and thirteen studies were included in the meta-analyses. Quantitative analyses showed significant differences in the comparisons of frail (standardized mean difference (SMD)—1.31, 95% confidence interval (CI) (−2.47, −0.15), p = 0.0271) and pre-frail (SMD—0.79, 95% CI (−1.58, −0.003), p = 0.0491) subjects vs. non-frail subjects. Sensitivity analyses reduced heterogeneity, resulting in a smaller but still highly significant between-groups difference. Results obtained indicate that lower 25(OH)D levels are significantly associated with increasing frailty severity. Future challenges include interventional studies testing the possible benefits of vitamin D supplementation in older adults to prevent/palliate frailty and its associated outcomes.
Highlights
Vitamin D is a fat soluble secosteroid hormone which is mainly produced endogenously in the skin (80–90%) after sunshine exposure
Cross-sectional or longitudinal design observational studies conducted in humans, including populations of older adults (≥60 years old), and written in English or Spanish were considered eligible for this systematic review
The search term included as the first descriptor was related to frailty (“frail*”), and the second one included descriptors related to vitamin D
Summary
Vitamin D is a fat soluble secosteroid hormone which is mainly produced endogenously in the skin (80–90%) after sunshine exposure. Vitamin D has a plethora of functions; the major physiologic function is regulating calcium and phosphate homeostasis as well as mineral bone metabolism. Vitamin D plays an extensive role as a cell differentiating and antiproliferative factor with actions in a variety of tissues, including the renal, cardiovascular, and immune systems [2,3]. 25-hydroxyvitamin D (25(OH)D) is the major circulating metabolite of vitamin D and is globally accepted as a marker of vitamin D status. There is no consensus about the cut-offs of this metabolite to describe an individual’s vitamin D status. The Institute of Medicine and the Endocrine Society have different definitions for vitamin D deficiency and optimal values [4,5]
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