Best and Worst Natural Cold and Flu Remedies

Find out which immune-boosting supplements really help—and which are just hype.

By the Editors of Prevention

Flu shots, hand washing, healthy eating, and regular exercise are the best ways to avoid cold and flu.

But sometimes even the most scrupulous germphobes and healthy people get sick anyway. While certain natural remedies can help shorten symptoms—or prevent infection entirely—many people waste money on measures that are all hype. Here's how to know the difference so you can get well faster—without wasting a penny.

1. Omega-3 Pill

The Verdict: Help

Take it: All season

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. Or get your omega-3s from these power foods.

2. Astragalus

The Verdict: Help

Take it: All season

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.

3. Echinacea

The Verdict: Hype

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.

4. Vitamin D

The Verdict: Help

Take it: All season

This power nutrient may effectively boost immunity and help prevent colds, a Harvard study shows. People with the lowest vitamin D levels were 36 percent 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., M.D. Aim for at least 1,000 IU daily.

5. Cold-fX

The Verdict: Help

Take it: When you feel sick

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.

6. Airborne

The Verdict: Hype

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.

See more cold and flu old wives tales and myths debunked here.

7. Zinc

The Verdict: Help

Take it: When you feel sick

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, M.D., M.P.H., 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.

9 Power foods that help boost your immunity.

8. Vitamin C

The Verdict: Hype

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.