Runners: You Need Vitamin D

Want to run faster? Get outside -- vitamin D will help you speed up.

According to studies, regular doses of vitamin D can shave an impressive 18 minutes off your marathon time. And you don't need to invest in costly supplements to get your fix -- the best way to get vitamin D is by spending more time in the sun -- with sunscreen and a hat, of course.

But even if you're not a hard-core marathon runner, you should still be getting vitamin D -- it also helps you lose weight.