The sunshine vitamin — vitamin D — is the latest target for researchers investigating treatment options for the coronavirus. Previous research has shown that the vitamin, which mainly comes from exposure to the sun and is essential for a healthy immune system, can help protect against other respiratory infections. Now, Spanish researchers have started a ten-week trial to see if vitamin D can also help with Covid-19. So should we all be taking a daily supplement to reduce our chances of getting the coronavirus or to help our bodies fight it?