Immune-Boosting Superfoods

By Rachel Johnson, Ph.D, M.P.H., R.D., November/December 2008

Can the right diet bolster my body’s defenses?

Never one to miss a celebration, I always look forward to holiday gatherings. But crowded parties are a prime place to pick up a bug. Couple that with late nights, frequent travel, and I know I’m a target for a cold or the flu. That’s why I try to boost my immune system to help keep me from missing out on the fun of this season.

To fight off colds, our son Ben, who’s 24, used to swear by Airborne, a supplement containing 17 vitamins, minerals and herbs that once billed itself as a way to prevent or cure colds. I was always skeptical that this supplement could work. I struggled not to say a motherly “I told you so” when, after settling a $23.3 million class-action lawsuit for false advertising, Airborne’s manufacturer was ordered to pay out an additional $30 million to consumers. Afterward, Ben admitted that Airborne had lost some of its appeal, but I still noticed it around his house. (The claim on the supplement now reads, “helps support your immune system.”)

For Ben’s sake and mine, I decided to take a look at the science and see what may really work to boost our immune systems—and what isn’t worth the money.


Vitamin-Mineral Potions and Pills

As with many label claims, Airborne’s current one begins with a kernel of truth: vitamins A, C, E, zinc, and selenium—nutrients in the supplement—are among the vitamins and minerals that our immune systems need to function efficiently. According to a 2002 report in the British Journal of Nutrition, deficiencies of any of these nutrients (or of vitamins B6, B12, folic acid, copper or iron) can depress immunity. But the key word is deficiency; most of us—save for smokers, pregnant and breastfeeding women and the elderly—meet our needs for these nutrients with the foods we eat. If you fall into any of those higher-risk categories, talk with your doctor before taking a supplement.

And more isn’t better. Excess amounts of many nutrients are potentially harmful, and it’s all too easy for even a bright, well-educated person like Ben to go overboard. Just one tablet of Airborne contains 1,667 percent of the daily recommended value (DRV) for vitamin C. After doing the math, I was stunned to discover that when he popped five Airborne tablets in a day—two more than the label recommends—he was getting two and a half times the established safe upper limit for vitamin C (excesses can cause gastrointestinal disturbances and kidney stones). He also came dangerously close to the upper limit for vitamin A, raising his risk of toxicity.

Glacéau’s Vitaminwater “Defense,” a drink with a label that claims it is “specially formulated with nutrients required for optimal functioning of the immune system,” doesn’t deliver the mega-high doses of nutrients that Airborne does. (A 20-ounce bottle of the water contains 150 percent of the DRV of vitamin C and 25 percent for four B vitamins and zinc.) But at 125 calories per bottle, I’d rather skip it.

A daily multivitamin/mineral supplement might come in handy this time of year, but I wouldn’t risk your health or waste your money on anything beyond that. So what does work?


A Cup (or More) of Green Tea

My colleague Mingruo Guo, Ph.D., a professor of food science at the University of Vermont and an authority on the immune-boosting potential of foods, always has a pot of green tea brewing. He drinks five to six cups a day, convinced that it has immune-enhancing effects along with other health benefits. Guo, who grew up drinking tea in China, credits tea’s polyphenols, potent plant antioxidants. One laboratory study suggested that a particular type of polyphenols called catechins may kill influenza viruses. Although just how they work isn’t fully known, research suggests that catechins, a particular type of polyphenols in green tea, may stimulate production and activity of some immune cells and inhibit the production of disease-promoting inflammatory compounds. One laboratory study found that catechins can kill influenza viruses.

Guo notes that many Americans are turned off by the bitterness of green tea—one downside of the polyphenols. But proper brewing techniques can help. To maximize benefits and minimize bitterness, the Tea Council recommends using just-below-boiling water and steeping green tea no more than a minute or two. A little lemon and honey can also help blunt the bitterness. But don’t add milk, because the proteins will bind to the polyphenols, making them ineffective.



Probiotics, so-called “good bacteria” found in yogurt, sauerkraut and other foods, are touted as helping prevent the GI upsets many of us succumb to during the holidays. According to a recent review in the Journal of the American Dietetic Association, regular consumption of probiotics may help your immune system work better, reduce the incidence of intestinal infections and improve digestion.

How do these seemingly magical bacteria work? Guo explains: The colon has as many as 100 billion microbes per gram of its content (almost half the weight of the colon for those who eat a typical Western diet)—some good, some bad. Good health depends on a balance. “GI distress happens when we have too many ‘bad’ microbes that produce toxins,” he says. Taking probiotics regularly can help “by lowering the pH of the colon, which is better for good microbes and inhibits the growth of bad microbes and may boost our immune capability.”

To stay healthy, Guo has a cup of probiotic soy yogurt every day (he doesn’t consume dairy because he is lactose intolerant). Fermented dairy products like yogurt or kefir (a yogurt-like beverage) are also good bets. Look for those labeled with a “Live & Active Cultures” seal from the National Yogurt Association, which signifies that the yogurt contains a set minimum amount of two particular types of beneficial bacteria. (While it’s not a guarantee of probiotic power—the bacterial counts don’t differentiate between added probiotic organisms and the bacteria that’s used to ferment the yogurt—the seal is a helpful start.) With the new “probiotic” cereals and granola bars, it’s not always clear how much good bacteria the manufacturers actually add to the products or whether the strains included are effective. If you really want to know about the science backing a product’s “probiotic power,” contact the manufacturer.

The Bottom Line

If you’re not eating as well as you usually do this holiday season, consider taking a multivitamin/mineral supplement—one with no more than 100 percent of the DRV—as extra insurance. It can’t hurt to include a daily serving of a probiotic-rich food and drink a cup of green tea whenever you can. I know I’ll be having yogurt with my morning cereal and fruit. And Ben—I know you’re reading this—I don’t want to nag, but maybe now you’ll give up the Airborne and try green tea instead?

Rachel K. Johnson, EatingWell’s senior nutrition advisor, is a professor of nutrition and food sciences at the University of Vermont.