In a study of college students—who are often under stress and short on sleep, two factors that increase risk of illness—those who took a probiotic supplement daily for 12 weeks had shorter and less-severe colds. Make sure your yogurt’s label says it contains “live and active cultures” (the ingredients will list specific strains, such as Lactobacillus bulgaricus or L. acidophilus).
Sweet potatoes are a great source of vitamin A (a small spud packs more than 200 percent of your daily value), which is essential in stimulating the body’s response to infection, explains a 2011 study in the journal Immunity. Plus, vitamin A helps keep your skin—your body’s first line of defense against bacteria and viruses—strong and healthy.
There are few food sources of vitamin D, but just three ounces of this fish supplies more than 100 percent of your daily need. People with the lowest levels of D were about 36 percent more likely to report an upper respiratory infection than those with the most, according to a study in the journal JAMA Internal Medicine. That’s especially important because adequate D levels can be hard to get in Northern climates in the winter.
Long used medicinally to improve immunity and even fight cancer, one animal study from Tufts University found that a supplement derived from white button mushrooms helps increase the activity of natural killer cells—aggressive white blood cells that fight tumors and viruses. Shiitake mushrooms have also been credited with protective powers, so throw a handful into your next stir-fry.
Sating your chocolate craving means giving yourself a dose of potent phytochemicals called flavonoids that support T-helper immune cells, which increase your natural defenses against infections, suggests a 2009 study in the British Journal of Nutrition. Dark chocolate is the best choice, as it contains higher levels of cocoa, the source of flavonoids.
Here’s a reason to switch from coffee to tea: the brew is packed with antioxidant compounds called catechins (specifically, one called epigallocatechin gallate, or EGCG) that have antiviral capabilities. In lab tests, green tea compounds were shown to stop flu viruses from replicating.
This oily fish has an impressive amount of omega-3s (1,200 mg in only three ounces of canned mackerel), health-promoting fatty acids that may enhance immunity by activating B cells. These fighter cells discharge antibodies, the body’s army that attacks invaders that make you sick, according to new research. You’ll often find mackerel canned or frozen at the grocery store.
A half cup of cooked spears supplies one-third of your daily need for folate. Getting enough of this nutrient is crucial for immune function; deficiency decreases the production of white blood cells that are released in response to infection. Other sources of the vitamin? Spinach, endive, mustard greens, and okra.