By Lisa Salmon. Vitamin D is known to play a vital role in a range of functions, and is key for keeping our bones, teeth and muscles healthy. There's now also growing interest in whether it could help protect against Covid-19. Scientists from Queen Mary University of London are launching a new trial to investigate whether vitamin D protects against the virus, as there's already evidence that it might reduce the risk of respiratory infections, with some recent studies suggesting people with lower vitamin D levels may be more susceptible to coronavirus. "Many people in the UK have low vitamin D levels, particularly in the winter and spring, when respiratory infections are most common," says lead researcher Professor Adrian Martineau. "Vitamin D deficiency is more common in older people, in people who are overweight, and in black and Asian people - all of the groups who are at increased risk of becoming very ill with Covid-19."