Experts today raise doubts about the effectiveness of vitamin D supplements to protect against acute and chronic disease.
The vitamin is made naturally in the body and has been linked to protection against bone decay and conditions such as multiple sclerosis.
But the use of supplements has proved controversial and the latest study today says there is little evidence to back them – and that vitamin D levels may merely indicate underlying states of health.
A review by researchers at the International Prevention Research Institute in Lyon, France, found that “the relation between vitamin D status and disorders are probably the result of confounding or physiological events involved in these disorders”.
Professor Philippe Autier and colleagues came to the conclusion after analysing data from 290 prospective observational studies and 172 randomised trials, all of which examined the effects of vitamin D levels on health outcomes that were not related to bones up to December 2012.
The findings of the large systematic review, published in the latest edition of The Lancet Diabetes & Endocrinology, casts strong doubt on the value of vitamin D supplements to protect against cancer, heart disease, diabetes, Parkinson’s disease, and death, challenging existing belief among many scientists that the vitamin has a potential role in disease prevention.
Vitamin D promotes calcium and bone formation but observational evidence has also suggested a link between an increased risk of many acute and chronic diseases due to inadequate levels of vitamin D.
However, Autier and his colleagues found that the benefits of high vitamin D concentrations from observational studies – including reduced risk of cardiovascular events of up to 58%, diabetes of up to 38%, and colorectal cancer by up to 34% – were not confirmed in randomised trials.
Meta-analyses of recent randomised trials did not identify any effect of raising vitamin D concentrations with supplementation on disease occurrence, severity, or clinical course.
“What this discrepancy suggests is that decreases in vitamin D levels are a marker of deteriorating health,” says Prof Autier.
“Ageing and inflammatory processes involved in disease occurrence and clinical course reduce vitamin D concentrations, which would explain why vitamin D deficiency is reported in a wide range of disorders.”
Autier P et al. Vitamin D status and ill health: a systematic review. The Lancet Diabetes & Endocrinology. December 6, 2013. [abstract]
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