Omega-3 Pill
If you don't like or eat a lot of fish, pop an omega-3 supplement daily to reap the fatty acid's impressive immune-fortifying properties. Omega-3s increase the activity of phagocytes—cells that fight flu by eating up bacteria—according to a study by Britain's Institute of Human Nutrition and School of Medicine. Other research shows that omega-3s increase airflow and protect lungs from colds and respiratory infections.
Look for purified fish oil capsules that contain at least 1 g combined of EPA and DHA.
Astragalus
This Chinese root is shown to stimulate the white blood cells that fight infection, says Prevention advisor Andrew Weil, MD. A study published in 2007 found that astragalus appears to boost immunity in mice. And a pilot study suggests that the herb may have similar effects in people. However, keep in mind that astragalus may take 6 to 8 weeks to reach its full effect.
Echinacea
If taken at the start of a cold, this herb might shorten duration and severity of symptoms. But some brands don't contain the amount of echinacea listed on the label—and some formulas have none at all. Possible side effects include wheezing, rash, and diarrhea.
Vitamin D
This power nutrient may effectively boost immunity and help prevent colds, a Harvard study shows. People with the lowest vitamin D levels were 36% more likely to have upper respiratory infections, compared with those with the most D. (Asthma patients with low levels of D were nearly 6 times as likely to get sick as those with the greatest amounts.) Adequate amounts of D help produce cathelicidin, a protein with virus-killing qualities.
Since it's tough to get enough from sunlight or diet (fish and fortified dairy are the best sources), you'll need a supplement to attain optimal levels, says study author Carlos A. Camargo Jr., MD. Aim for at least 1,000 IU daily.
Cold-fX
Consider taking this supplement, which contains North American ginseng extract, when you feel a cold coming on. Subjects who took two daily capsules of Cold-fX (available online) caught half as many colds as a group taking a placebo, according to a study by the Center for Immunotherapy of Cancer and Infectious Diseases at the University of Connecticut. When they did get sick, their symptoms lasted less than half as long. This particular ginseng variety contains compounds that increase white blood cells and interleukins, proteins the immune system relies on.
Airborne
Experts say this supplement, a blend of blend of Zinc, Ginger, Echinacea and other vitamins, minerals, and herbs, does nothing to repel germs on an airplane or anywhere else. It also contains large amounts of vitamin A, which could be toxic if taken several times a day.
Zinc
The research on this mineral is conflicting. Still, "30 mg taken at the very start of a cold will shorten it by about half a day," says David L. Katz, MD, MPH, director of the Yale University Prevention Research Center. Look for Zicam or Cold-Eeze. By slowing the multiplication of the virus in the nose and throat, these products appear to shorten colds.
But don't overdo it. While even a slight deficiency in zinc, which is needed to produce white blood cells, can increase your risk of infection, more than 50 mg daily can suppress your immune system and block absorption of other essential minerals.
Vitamin C
There's certainly no downside to eating a lot of C-rich foods, such as red peppers and citrus fruits. But taking a vitamin for extra protection won't help. A 2007 review of 30 studies found no evidence that vitamin C supplementation prevents colds in the normal population. Plus, megadoses can cause kidney stones, upset stomach, and even internal bleeding in children.
