An eight-year French study of 535 adults ages 20 to 44 found that those with the highest blood levels of beta-carotene retained 30 percent more lung function than those with the lowest—enough to counteract the effects of about four months of aging and exposure to damaging substances in the air, explains Norman H. Edelman, M.D., chief medical officer of the American Lung Association. Incorporating beta-carotene-rich foods such as cantaloupe, watermelon, and sweet potatoes into your recommended five to nine servings of fruits and vegetables each day may help you gain these protective benefits. If you are a smoker, avoid beta-carotene supplements, which some studies have found may increase the risk of lung cancer by roughly 20 percent. —Holly St. Lifer