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)…regular 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.