Finnish researchers discovered that vitamin D can keep you from getting sick. In a six-month study of 756 men, they found that those with the lowest blood levels of the vitamin took twice as many sick days for respiratory infections as the men who weren’t deficient.

That’s because vitamin D stimulates the production of antibiotic-like chemicals in your respiratory tract, helping to destroy bacteria before they can cause harm, says study author Dr Ilkka Laaksi. Harvard doctors recommend a daily intake of 1 000 international units (IU) of vitamin D.