Despite data from recent meta-analyses of vitamin D supplementation without co-administration of calcium failing to demonstrate fracture prevention, almost half of older adults continue to use these supplements. This systematic review was conducted to investigated whether vitamin D supplementation affects bone mineral density (BMD). It included 23 randomised trials (mean duration 23.5 months, n= 4082, 92% women, average age 59 years) of which 19 studies had mainly white populations. These studies compared interventions that differed only in vitamin D content, and which included adults without other metabolic bone diseases. The primary endpoint was the percentage change in BMD from baseline.
The mean baseline serum 25-hydroxyvitamin D concentration was <50 nmol/L in 8 studies (n=1791). In 10 studies (n=2294), patients received vitamin D doses <800 IU per day. There were six findings of significant benefit, two of significant detriment, and the rest were non-significant. Only one study showed benefit at more than one site. Results of meta-analysis showed a small benefit at the femoral neck (weighted mean difference 0.8%, 95% CI, 0.2 to 1.4) with heterogeneity among trials. No effect at any other site was reported, including the total hip.
Based on these findings, the researchers suggest that the widespread use of vitamin D supplements for skeletal protection in adults without specific risk factors for vitamin D deficiency is not justified. They note that their findings support those from previous meta-analyses of fracture studies. They add that individuals at risk of vitamin D deficiency as a result of skin pigmentation or low sunlight exposure might indeed benefit, so targeting of the intervention is important if the balance of risk and benefit is to be positive. They call for further studies of vitamin D supplements in these groups to establish links between baseline 25-hydroxyvitamin D concentration and responses to vitamin D supplements, and possibly to an improved definition of vitamin D deficiency. In addition, the increasing practice for measurement and supplementation of vitamin D is expensive and they suggest that the targeting of low-dose vitamin D supplements only to individuals who are likely to be deficient could free up substantial resources that could be better used elsewhere in health care.
An accompanying Comment article discusses how these surprising findings can be reconciled with clinical practice and public health strategies to prevent osteoporosis. The author concludes that this meta-analysis is consistent with current understanding of vitamin D in that supplementation to prevent osteoporosis in healthy adults is not warranted. However, maintenance of vitamin D stores in the elderly combined with sufficient dietary calcium intake (800–1200 mg per day) remains an effective approach for prevention of hip fractures.
Guidance on vitamin D and bone health was recently published by the National Osteoporosis Society (NOS). NICE is currently developing guidance to help safely implement existing evidence-based recommendations on the prevention of vitamin D deficiency. It will focus on at-risk groups including infants and children aged under 5, pregnant and breastfeeding women, older people, people with dark skin and those who have limited exposure to the sun.