Vitamin D reduces the risk of falls in older adults compared with calcium or placebo
- Correspondence to Melissa J Benton
PhD, RN, CNS, FACSM, Valdosta State University, College of Nursing, 1500 N Patterson Street, Valdosta, GA 31698, USA;
Vitamin D deficiency in older adults has traditionally been of concern in relation to its role in maintaining bone mineral density. The effect of vitamin D on muscle strength and its influence on fall risk and prevention may have been underappreciated. A growing body of literature now focuses on the use of vitamin D for prevention of muscle atrophy, in particular type II muscle fibers that are associated with strength and function. Although by no means conclusive, research has now moved from initial cross-sectional analyses to interventional studies measuring changes in strength and muscle fiber size secondary to supplementation with vitamin D. This research has direct applications to fall prevention.
Effective prescription of vitamin D
Prevention of falls is of critical importance for quality of life and economic reasons. Kalyani and colleagues have provided the most inclusive meta-analysis to date of high quality, randomised controlled clinical trials evaluating the effect of vitamin D on falls in older adults in community, institutional and hospital settings. Their search strategies have identified for inclusion the largest number of fall-related studies of any review or meta-analysis to date. On the basis of available data from 10 well-designed randomised controlled trials, the authors concluded that supplementation with greater than 800 IU of vitamin D combined with calcium for at least 6 months is most effective, especially for community-dwelling individuals younger than 80 years of age, without a history of fracture or falls. Furthermore, the cholecalciferol form of vitamin D may be clinically (although not statistically) more effective than ergocalciferol. These findings can be useful for nursing practice, as they provide a foundation for the appropriate prescription of vitamin D for older individuals. However, nurses need a greater understanding of the activity of vitamin D in the body to support their role in client/patient education.
Vitamin D and muscle function
Muscle fibers contain vitamin D receptors that influence protein synthesis, muscle mass and the development of sarcopenia.1 Type II muscle fibers are selectively lost with ageing, and their loss is typically accompanied by commensurate decreases in strength and function that contribute to the onset of frailty. Supplementation with vitamin D results in increased size and relative number of type II muscle fibers in concert with improvements in muscle strength and function.2 The protective activity of vitamin D in relation to type II muscle fibers provides the most likely mechanism for its role in fall prevention.
Confounding effect of vitamin D status
Giovannucci3 recently published an excellent summary of the current research regarding vitamin D and muscle function that reminds us of the critical role deficiency plays within at-risk populations – an area that the findings of Kalyani and colleagues have not addressed. The review by Giovannucci builds on a previous analysis by Janssen and colleagues4 which clearly demonstrates that when deficiency exists, vitamin D supplementation may selectively delay or reverse atrophy of type II muscle fibers, with resultant increases in strength. However, in vitamin D-replete individuals, supplementation appears to have no additive effect on strength or function. Furthermore, loss of muscle and strength inevitably occurs with ageing, even in the presence of adequate serum vitamin D levels. It would appear, therefore, that vitamin D may play a role in the pathological consequences of deficiency but does not uniformly exert a protective effect on the loss of muscle and strength that normally occurs with age.
The only effective strategy for the maintenance of muscle and strength during healthy ageing is resistance training. Research is needed to evaluate the potential benefits of adding vitamin D supplementation to resistance training programmes for older adults. Only one such study is currently available through the PubMed database. Bunout and colleagues5 administered low-dose vitamin D with calcium, calcium alone, or placebo to vitamin D-deficient older adults during a 9-month resistance training programme. Although resistance training improved muscle strength in all participants with or without supplementation, vitamin D provided an additive effect on gait speed, which is tied to functional ability. These findings support the need for further research and also the recommendations of Kalyani and colleagues that vitamin D supplementation be incorporated into clinical practice to reduce risk for falls in older adults.