A new review from France suggests that existing study data indicating that increased blood vitamin D concentrations are associated with a reduction in the risk of chronic diseases, such as cardiovascular events, diabetes and related mortality, does not prove that vitamin D supplementation can prevent those diseases. Experts commented that, although evidence in non-bone-health-related chronic disease prevention is missing, there is good reason to ensure that the vitamin D supply is adequate.
The analysis included results from 290 prospective observational studies that investigated potential links between blood vitamin D concentrations and markers of several chronic diseases (1). The analysis showed that high blood vitamin D levels were associated with an up to 58% reduction in the risk of cardiovascular events, an up to 38% reduction in the risk of diabetes, an up to 33% reduction in the risk of colorectal cancer, and an up to 29% reduction in the risk of all-cause mortality. High vitamin D concentrations were also associated with improvements in cholesterol levels, markers of inflammation, glucose metabolism disorders, infectious diseases, weight gain and cognitive function. On the other hand, the analysis of data from a total of 172 randomized controlled trials evaluating the potential non-bone-health-related effects of vitamin D supplementation indicated no significant reduction in chronic disease risk.
The researchers concluded that low vitamin D levels may not be a cause but a consequence of ill health. Aging and inflammatory processes involved in disease occurrence may reduce vitamin D concentrations, which would explain why vitamin D deficiency is reported in a wide range of disorders. The researchers speculated that, as the non-bone-health-related benefits of high vitamin D concentrations shown by data from observational studies have not been reproduced in most randomized trials, the relation between vitamin D status and disorders is probably the result of confounders or unknown physiological events involved in these disorders.
Experts commented that vitamin D research is complex as the vitamin status can be influenced by several factors (e.g., time spent outdoors at sun exposure, sun-safe behaviors, reduced production in skin with age, consumption of vitamin D rich foods such as oily fish). In addition, the development of chronic diseases depends on multiple lifestyle and genetic factors, and the biological changes that lead to these diseases often start decades before diagnosis. Currently, five big clinical trials (VITAL, VIDAL, ViDA, DOHealth and FIND) testing vitamin D3 for a variety of outcomes in participants over 50 years of age are underway. According to the scientists, adequate blood vitamin D concentrations are essential for good health. However, the vitamin has been identified in surveys worldwide as a micronutrient of which the majority of people have an insufficient supply (for example, because they do not get enough vitamin D from foods, spend a lot of time indoors, or live in an area where the skin cannot produce vitamin D in the winter). For such circumstances, vitamin D supplementation in adequate doses can be a safe and beneficial way to achieve healthy levels. Nevertheless, it may be unrealistic to expect that vitamin D in isolation from other healthy habits will prevent a multifactorial disorder such as cancer or cardiovascular disease.