Up to 36 percent of Americans might be deficient in vitamin D, research suggests. Low levels have been linked to autoimmune disorders, cancers, heart disease, and osteoporosis. Talk with your doctor about whether you need a blood test. Boost vitamin D by consuming fortified milk, salmon and other fatty fish, or supplements. Sunlight also supplies vitamin D. Most people need 10 minutes outdoors without sunscreen three or four times a week. Those who are overweight, over 50, have darker skin or live in the North need more.

Read more on the benefits of vitamin D (free), getting more vitamin D in your diet (free), and on how it can help in the prevention of osteoporosis (subscribers only).