By Brierley Wright, M.S., R.D. , December 1, 2010 - 11:47am
The much-dreaded cold and flu season is upon us. And if you’re like me, there isn’t any spare time built into the schedule to be sick. So how can I bolster my defenses against the germs lurking in the common areas in my office, the mall where I do my holiday shopping and the rest stops I encounter in my holiday travels?
Related: Delicious recipes to help boost your immune system 
I took a look at the research Emily Sohn and Rachel Johnson, Ph.D., M.P.H., have written about for EatingWell and pulled together a list of what’s worth trying—and what’s not.
Try It: Vitamin D
In a study published recently in the American Journal of Clinical Nutrition, children who took daily vitamin D supplements (1,200 IU) were 40 percent less likely to get a common flu virus than kids who took a placebo. Laboratory studies indicate that the nutrient may help immune cells identify and destroy bacteria and viruses that make us sick, says Adit Ginde, M.D., M.P.H., a public health researcher at the University of Colorado School of Medicine in Denver.
Although the Institute of Medicine released in a report November 30 new recommendations for vitamin D (600 International Units per day for everyone, except men aged 71+ who should get 800 IU), they “only focused on bone health,” says Ginde. “There is not yet enough evidence to definitely prove that vitamin D reduces infections, but the amount recommended for bone health is lower than what we think is needed for improved immunity and reduced infections. Most people need at least 1,000 IU a day and some need 2,000 IU daily or higher to reach levels that appear necessary for optimal immune responses.” While many experts recommend a vitamin D supplement, you can also get it (in small doses) from fatty fish, such as salmon, and fortified milk—and your body makes vitamin D from the sun.
Try It: Green tea
Polyphenols, potent plant antioxidants, are what’s believed to give green tea its immune-boosting effects. One laboratory study suggested that a particular type of polyphenols called catechins may kill influenza viruses. To maximize benefits and minimize bitterness, use just-below-boiling water and steep 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.
Try It: Probiotics
Some research suggests that when these so-called “good” bacteria—found in yogurt, sauerkraut and other foods—reach the lower intestine, they not only suppress the growth of “bad” bacteria but also might activate the immune system to fight off diseases in other ways. But studies showing a clear boost to the immune system are few. In one study of 33 healthy young women, both “regular” yogurt and so-called “probiotic-fortified” yogurt (which contained added beneficial bacteria cultures) were found to boost T-cells, key players in the body’s defenses against viruses and other pathogens. But it’s a long way from findings like those to “assuming that by loading up on yogurt—or sauerkraut or kimchi—you can boost your immune system enough to fight off something like the H1N1 flu,” says Barry Goldin, Ph.D., professor in the department of Public Health and Community Medicine at Tufts University School of Medicine in Boston. Fortifying yourself with a daily dose of fermented foods can’t hurt, says Goldin, “but if you want to beat the flu, get vaccinated.”
Quick tip: Look for fermented dairy products, such as yogurt or kefir (a yogurt-like beverage), that are labeled with a “Live & Active Cultures” seal from the National Yogurt Association. The seal signifies that the yogurt contains a set minimum amount of two particular types of beneficial bacteria.
Related: Healthy Breakfasts With Yogurt 
Try It: Soluble Fiber
Mice that ate a diet rich in soluble fiber for six weeks recovered from a bacterial infection in half the time it took mice that chowed on meals containing mixed fiber, according to a recent study in the journal Brain, Behavior and Immunity. Soluble fiber—abundant in citrus fruits, apples, carrots, beans and oats—helps fight inflammation, says lead author Christina Sherry, Ph.D., R.D., of the University of Michigan, Ann Arbor. Insoluble fiber—found in wheat, whole grains, nuts and green leafy vegetables—is still important for overall health, but it doesn’t seem to have the same impact on immunity. Strive for 25 to 38 grams of total fiber a day, Sherry says, paying extra attention to getting the soluble kind.
Related: High-Fiber Breakfasts You Can Grab & Go 
Skip It: Airborne
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 women, 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 to go overboard. Just one tablet of Airborne contains 1,667 percent of the daily recommended value (DRV) for vitamin C.
Skip It: Glacéau’s Vitaminwater “Defense”
This 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.) Plus it delivers 125 calories per bottle.
Updated December 6.
What do you eat to keep sickness at bay? Tell us what you think below.