Researchers have known that healthy vitamin D levels are important to keep bones strong, protect immune function, and even improve mental health. Recent research shows it may also reduce risk of COVID-19 infection. In a University of Chicago Medical Centre study, patients with healthy vitamin D levels were around half as likely to test positive for COVID-19 than those with a deficiency. That’s particularly important now we’re heading into winter, when the sun’s not strong enough to synthesise vitamin D in our skin. A supplement may be the best bet for most people in the UK.