source of vitamin d

Photo: Shestock/Getty Images

1 of 6
Vitamin D

Why you might be low: If you live in a northern climate or you're a diligent sunscreen user (and, ahem, we should all fall into that category), you're at risk for a vitamin D deficiency. (Your skin produces vitamin D when it's exposed to sunlight, but not when sunscreen is blocking the UV rays.) In fact, "the number one vitamin that patients I see are low in is vitamin D," says Holly Thacker, MD, director of the Center for Specialized Women's Health at the Cleveland Clinic.

Why you need it: Your body needs vitamin D to absorb calcium, so not getting enough could lead to weak bones. There's also research suggesting that adequate intake could help prevent certain cancers and may play a protective role against chronic illnesses like high blood pressure, heart disease and diabetes. Plus, some studies suggest a link between low vitamin D and depression.

Where to find it: Fish like swordfish, salmon and tuna are excellent sources, as are dairy products including yogurt, cheese and milk (especially if it's fortified with Vitamin D, as many milks are). Eggs are also a good source—just make sure you're not relying on egg white omelets for your intake, since vitamin D is found in the yolks.