*1. Fill your Vitamin D tank
You may have fewer health problems—ranging from colds to cancer—if you get enough vitamin D. Your body naturally makes vitamin D from sunlight. You can also get it—albeit in smaller doses—from fatty fish, such as salmon, and fortified milk. But because Americans don’t get enough vitamin D, most experts recommend a D supplement. New research in the American Journal of Clinical Nutrition suggests that taking such a supplement may help boost your immune system. In a study of more than 300 Japanese children, those who took daily vitamin D supplements (1,200 IU) were 40 percent less likely to get a common flu virus than kids who took a placebo. Laboratory studies indicate that the nutrient may help immune cells identify and destroy bacteria and viruses that make us sick, says Adit Ginde, M.D., M.P.H., a public health researcher at the University of Colorado School of Medicine in Denver. Aim to get at least 1,000 IU of vitamin D daily (check with your doctor before taking more).
*2. Get a daily dose of soluble fiber
Mice that ate a diet rich in soluble fiber for six weeks recovered from a bacterial infection in half the time it took mice that chowed on meals containing mixed fiber, according to a recent study in the journal Brain, Behavior and Immunity. Soluble fiber—abundant in citrus fruits, apples, carrots, beans and oats—helps fight inflammation, says lead author Christina Sherry, Ph.D., R.D., of the University of Michigan, Ann Arbor. Insoluble fiber—found in wheat, whole grains, nuts and green leafy vegetables—is still important for overall health, but it doesn’t seem to have the same impact on immunity. Strive for 25 to 38 grams of total fiber a day, Sherry says, paying extra attention to getting the soluble kind.
*3. Stay lean
Overweight adults who cut their daily calorie intake by nearly a third saw a 50 percent boost in immunity, according to a six-month study out of Tufts University. (Those who cut calories by 10 percent had smaller improvements.) Restricting calories may reduce levels of compounds in the body that depress your immune response, says Tufts nutritional immunologist Simin Meydani, D.V.M., Ph.D. Animal studies suggest that calorie restriction could work in normal-weight individuals too. “Try to maintain your body weight at what is considered ideal,” Meydani says, because eating more than what you need drags the immune system down. And remember: when you cut back on quantity, you need to be even more vigilant about the quality of your diet. Aim to eat more fruits and vegetables—and choose lean protein sources, such as fish, chicken and low-fat dairy.