According to the latest report, approximately 75 percent of—yes, folks, that's 3 out of 4!—Americans have low vitamin D levels. This isn't good news considering the sunshine vitamin's link to a vast array of health benefits. Vitamin D supports heart and bone health, and can help ward off cancer, dementia, and even the common cold.

How do you know if you need more vitamin D? You rarely see the sun, have a general pallor ... no, really, you'll need a simple blood test to find out (see your doc). Once you know your levels are low, you'll need to get the right kind of vitamin D supplement for greatest efficacy and be aware that you may need to take more than the current recommendations. (Check out the links peppered in this paragraph for more.)