To help guard against viruses, you know about diligent hand-washing. But it’s also wise to follow a natural immune-boosting regimen that includes plenty of sleep (seven to eight hours a night)…a healthful diet (with lots of vitamin C–rich citrus fruit and berries)…exercise…and low levels of stress. In addition, these supplements have been found to help prevent viral illnesses…

Vitamin D. Evidence: Adults with low levels of vitamin D (below 10 ng/mL) who took a vitamin D supplement daily or weekly had half the risk of developing an acute respiratory infection, such as the flu or a cold, according to research published in The BMJ

My advice: Get your vitamin D levels tested, and if low, take 2,000 to 4,000 international units (IU) daily.

American ginseng. Evidence: When nursing home residents took a 200-mg capsule of an American ginseng extract product called COLD-FX twice daily, their risk for the flu was 89% lower than a placebo group, according to research published in Journal of the American Geriatrics Society. 

My advice: Talk to your doctor about trying American ginseng. Be sure it’s American ginseng—not Asian, Siberian or other ginseng varieties. Important: American ginseng may interact with medication, including blood thinners, diabetes drugs and monoamine oxidase inhibitor (MAOI) antidepressants, so be sure to consult your doctor.