A major review on the health benefits of the sunshine vitamin, D, has found no clear positive effects, researchers say today.
Many studies have been undertaken on the role of vitamin D in a variety of aspects of health. These are often inconclusive or not rigorous enough, say Dr Evropi Theodoratou of Edinburgh University, UK, and colleagues in the British Medical Journal.
Vitamin D is generated in the body through exposure to sunshine.
They reviewed the evidence from dozens of reviews and meta-analyses of vitamin D studies, explaining: "The relation between vitamin D and 137 outcomes has been explored, covering a wide range of skeletal, malignant, cardiovascular, autoimmune, infectious, metabolic, and other diseases."
They found that vitamin D may benefit birth weight, dental caries in children, and hormone levels in kidney dialysis patients, but even so, "further studies and better designed trials are needed to draw firmer conclusions".
They add: "In contrast to previous reports, evidence does not support the argument that vitamin D supplementation increases bone mineral density or reduces the risk of fractures or falls in older people.
"Despite a few hundred systematic reviews and meta-analyses, highly convincing evidence of a clear role of vitamin D does not exist for any outcome, but associations with a selection of outcomes are probable," they conclude.
In a second paper, a team led by Dr Oscar Franco of Erasmus MC, University Medical Centre, Rotterdam, The Netherlands, looked at vitamin D’s link to death from cardiovascular disease or cancer.
An analysis of several observational and randomised trials found that low vitamin D levels in the blood were linked to increased death risks from cardiovascular disease, cancer, and other causes.
But "further clinical investigations will be essential to establish the optimal dose, duration and safety," they write.
Theodoratou, E. et al. Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomised trials. BMJ 2 April 2014 doi: 10.1136/bmj.g2035
Chowdhury, R. et al. Vitamin D and risk of cause specific death: systematic review and meta-analysis of observational cohort and randomised intervention studies. BMJ 2 April 2014 doi: 10.1136/bmj.g1903 [abstract]
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