Sun supplement

Taking vitamin D in winter may give at-risk groups an immune boost as well as helping bone health.

- Jennifer Bowden

Question: Do we need vitamin D supplements during winter? Or is sun exposure sufficient?

Answer: Vitamin D has long been known for its essential role in bone metabolism and the prevention of rickets. Recent evidence suggests vitamin D also modulates our immune response to infectious diseases. For example, vitamin D status has been linked to the severity and frequency of respiratory infections in children.

So, should we be focused on optimising our vitamin D status as a tool in our battle against the Covid-19 virus this winter? Low vitamin D status was associated with increased hospitalisation and mortality from Covid-19, but not with the chances of being infected with the disease, in a meta-analysis published in Critical Reviews in Food Science and Nutrition last year. This meta-analysis was a compilation of observational studies, so cannot prove a causal link between vitamin D status and Covid infection severity. But a recent US study compared the risk of Covid infection and severe outcomes among a group of war veterans who were already receiving vitamin D supplements with veterans who were not receiving them. The retrospective analysis found supplementation reduced the risk of infection by 20-28% and mortality by 25-33%.

DIETARY SOURCES

Vitamin D is found in small amounts in foods such as oily fish (eg, salmon, tuna, sardines, eel and warehou), milk and milk products, eggs and liver. Some margarines, spreads, dairy substitutes and liquid meal replacements contain added vitamin D.

Notably, those veterans with the lowest vitamin D status had the most substantial benefit from supplementation. It appears, then, that optimising our vitamin D status may reduce the risk and severity of a Covid-19 infection this winter.