Immunity-Boosting Tips to Stay Cold-Free

Discover the sneaky culprits that can bust your immunity -- and the proven strategies to instantly boost it.

Sneaky Cold Culprits

Colds are not sexy. But did you know that your sex plays a role in whether you catch one?

Young women fight off colds better than young men do, a new Australian study revealed. However, the gender advantage, which researchers suspect is related to hormones, disappears after menopause.

And decades before that, your immunity begins to wane in other ways. As you get older, some of your key defenses against colds and the flu, called naive immune system cells, dwindle, and this may contribute to an increased risk for getting infections and catching viruses. "The younger you are, the more naive immune system cells you have," says Rohit Katial, MD, director of allergy and immunology clinical services at National Jewish Health Hospital in Denver. "Every time you encounter an illness, these cells build immunity against the infection. When you come into contact with the same virus in the future, your immune system reacts stronger and faster, so you may not get sick at all." Unfortunately our bodies produce fewer new naive immune cells every year, making us less equipped to fight new germs, he says.

Your everyday habits can further chip away at your defenses. Check out the most surprising health saboteurs and learn how to boost your immunity and stay sniffle-free all season.

Cold culprit: Your sneakers are in hibernation.

Short days and frigid weather make it tempting to blow off workouts, but if you do, your immune system will suffer. People who exercised at least five days a week had 43 percent fewer days with a cold during the fall and winter than those who broke a sweat less often, according to a study from Appalachian State University in Boone, North Carolina. That's because during exercise and for three hours afterward, your body steps up the production of important germ-fighting cells called neutrophils. "Every time you work out, you're protecting yourself against getting sick," says study author David Nieman. Aim for two and a half hours of moderate physical activity weekly, such as doing your favorite workout DVD or walking. But don't overdo it. In a study, marathon runners who logged 60 miles a week or more were twice as likely to come down with colds as those who ran less. "Doing any kind of vigorous exercise for 90 minutes or more at a time can put your body at risk for illness," Nieman says. "At that threshold, your body perceives exercise as a stressor, and your immune system doesn't function well."

Cold culprit: You're feeling crazed at work.

"Chronic stress creates biochemical changes in the body that cause the immune system to function less efficiently," says Sandra A. Fryhofer, MD, a FITNESS advisory board member. To tame work tension, ask a coworker out to lunch or to join you for a short walk whenever you feel frazzled. "During social interactions our bodies release hormones, like oxytocin, that reduce levels of the stress chemicals cortisol and adrenaline," says Sharon Toker, PhD, a researcher at Tel Aviv University in Israel who found that employees with strong relationships at work live longer than those who don't have them.

Cold culprit: Pumpkin-spice lattes are your only source of vitamin D.

Seventy-seven percent of American adults are deficient in D, and they're 24 to 36 percent more likely to catch colds than people with higher concentrations of it, according to a recent study from the University of Colorado School of Medicine in Aurora. "Without adequate levels of vitamin D, immune cells produce fewer antibacterial proteins and are less efficient at killing viruses and bacteria," says study author Adit Ginde, MD. Get 1,000 international units of the vitamin a day by filling up on D-rich foods, such as fatty fish (salmon, mackerel, and sardines) and fortified milk and cereals, or by taking a daily supplement, Dr. Fryhofer says. Be sure to also spoon up plenty of D-fortified yogurt, which is rich in good-for-you probiotic bacteria. Research has shown that people who consumed probiotics regularly were 42 percent less likely to suffer from an upper respiratory tract infection than those who took a placebo.

Cold culprit: You wear flannel pj's to bed every night.

Get in the mood by regularly slipping into some silky, sexy sleepwear instead. People who have sex once or twice a week have a 30 percent higher concentration of disease-fighting immunoglobin A in their bodies, researchers at Wilkes University in Wilkes-Barre, Pennsylvania, found. This antibody -- the first line of defense against colds -- forms a barrier to pathogens, like viruses. It also binds to any pathogens that slip through and signals the immune system to destroy them. "During sex the body releases a surge of endorphins that strengthen the immune system, which probably accounts for the increase in immunoglobin A," say study author Carl Charnetski, PhD.

Cold culprit: You have the pizza delivery place on speed dial.

To stay fit this winter, reach for comfort foods that are loaded with fruits and veggies. "Without enough nutrients from produce, your immune system is ill equipped to prevent viruses from replicating and, in turn, making you sick," says Joel Fuhrman, MD, author of Super Immunity. Incorporate green vegetables -- especially spinach, kale, collard greens, bok choy, Brussels sprouts, lettuce, and broccoli -- into at least two meals every day. "Greens are packed with isothiocyanates, compounds that activate white blood cells, which fend off viruses and heighten the germ-fighting ability of natural killer cells," Dr. Fuhrman says. Cold-proofing your diet is easier than you think: Eat more salads and add leafy greens to soups and pasta dishes or top your pizza with them.

Cold culprit: You cocoon all winter long.

Curling up on the couch seems like a good way to shield yourself from illness, but it's not: Going out to hang with friends may actually keep you healthier. When researchers at Carnegie Mellon University in Pittsburgh exposed study participants to a cold virus, social butterflies with a lot of friends, work pals, and exercise buddies were less likely to get sick than homebodies. Part of the reason may be that supersocial people tend to take better care of themselves; they are healthier eaters and exercise more, says study author Sheldon Cohen, PhD, professor of psychology. So make a point to reply yes to as many invitations as you can, and schedule weekly dates with your BFFs.