There has been a mixed bag of reactions to vitamin D recently: a new study looks at whether low vitamin D levels are a cause or result of ill health.

In this study, researchers reviewed 290 observational studies and 173 randomised trials on vitamin D status and health. In most of the observational studies, there was a link between higher levels of vitamin D and lower risk of cardiovascular disease, lipid levels, markers of inflammation, glucose metabolism disorders, declining cognitive function, and impaired physical functioning. Researchers did however not find a link between increasing levels of vitamin D and lower risk of disease, and vitamin D supplements had little effect on these diseases. Supplementation was however linked with a slightly lower risk of all-cause mortality among older women, who tend to have very low levels of vitamin D. Other studies suggest that we should Make No Bones About Vitamin D and is a Cold Crushing D-Fence.

According to authors of the study, low vitamin D levels result from ageing and disease. Ageing can lead to reduced food intake, physical activity, and sun exposure, and it can impair the ability to synthesise vitamin D in skin. Disease can cause these things as well, and inflammation associated with disease is associated with lower vitamin D levels. Large randomized trials (some are now underway) are needed to test if vitamin D supplementation lowers the risk of chronic diseases in older adults.