Researchers have called for more randomised trials to determine whether vitamin D affects Covid-19 risk after a study suggested that vitamin D deficiency could increase the likelihood of becoming infected with the coronavirus.

An observational study published in Jama Open Network looked at whether patients' most recent vitamin D levels and treatment for insufficient vitamin D levels are associated with test results for Covid-19.

The research team looked at 489 University of Chicago Medicine patients whose vitamin D level was measured within a year before being tested for Covid-19. Patients who had vitamin D deficiency (<20ng/ml) that was not treated were almost twice as likely to test positive for the Covid-19 coronavirus compared to patients who had sufficient levels of the vitamin.

Vitamin D supplements could lower the risk of Covid-19 infections

David Meltzer, Chief of Hospital Medicine at UChicago Medicine and lead author of the study, said: "Vitamin D is important to the function of the immune system and vitamin D supplements have previously been shown to lower the risk of viral respiratory tract infections. Our statistical analysis suggests this may be true for the Covid-19 infection.

"Understanding whether treating vitamin D deficiency changes Covid-19 risk could be of great importance locally, nationally and globally. Vitamin D is inexpensive, generally very safe to take, and can be widely scaled."

Meltzer and his team emphasise the importance of experimental studies to determine whether vitamin D supplementation can reduce the risk, and potentially severity, of Covid-19. They also highlight the need for studies of what strategies for vitamin D supplementation may be most appropriate in specific populations. 

Vitamin D helps to control the amount of calcium and phosphate in our bodies. Both are needed for healthy bones, teeth and muscles.

Vitamin D is found naturally in a small number of foods, including oily fish, red meat, liver and egg yolks. It’s also found in fortified foods like breakfast cereals and fat spreads. However, it’s difficult for us to get the recommended amount of vitamin D from food alone. Our main source of vitamin D is from the action of sunlight on our skin.