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15 best (and worst) foods for immunity

by John Gomez | Last Updated: November 17, 2009

November 17, 2009 – Is your diet making you a germ magnet? Research shows that what you eat — or don’t — can play an important role in your immune system’s ability to do battle with incoming germs. Read on to see whether your fridge and pantry are stocked with these power foods, as well as whether you consume too many that can wreak havoc on your body’s germ-killing prowess.


Orange Juice – One cup with breakfast supplies more than 100 percent of your daily vitamin C requirement (75 mg a day for women and 90 mg a day for men). Best known for its skin and immunity benefits, vitamin C won’t prevent colds (contrary to popular belief), but studies show that consuming enough can help you recover faster, especially for people with low levels.

You’re best off getting C from food (other notable sources include red peppers and kiwifruit) as opposed to megadose supplements, which can cause kidney stones, upset stomach and even internal bleeding in children. In fact, a 2007 review of 30 studies found no evidence that vitamin C supplementation prevents colds in the normal population.

Oats and barley – These grains contain beta-glucan, a type of fiber with antimicrobial and antioxidant capabilities more potent than echinacea, reports a Norwegian study. When animals eat this compound, they’re less likely to contract influenza, herpes, even anthrax; in humans, it boosts immunity, speeds wound healing and may help antibiotics work better.

Milk – Along with fish, fortified dairy is one of the best dietary sources of vitamin D — a power nutrient that 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. Adequate amounts of D help produce cathelicidin, a protein with virus-killing qualities.

Because it’s tough to get enough D from diet and sunlight alone, it’s best to take a supplement to attain optimal levels, says study author Dr. Carlos A. Camargo Jr. Aim for at least 1,000 IU daily.

Yogurt – Shift workers who consumed a drink containing Lactobacillus reuteri, a probiotic that appears to stimulate infection-fighting white blood cells, were 33 percent less likely to take sick days than those who took a placebo, according to an 80-day Swedish study published in Environmental Health. But beware, says Elizabeth Somer, RD, author of 10 books on nutrition: “Some companies make up probiotic names to put on their label.” She suggests looking for yogurt that contains Lactobacillus acidophilus as well as Bifidus and L. rhamnosus. “They’re even more effective when combined,” she says.

Fish and shellfish – Salmon, mackerel, herring, and other fatty fish contain omega-3 fatty acids, which increase 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. They also contain selenium (also plentiful in shellfish such as oysters, lobsters, crabs, and clams), which helps white blood cells produce cytokines, proteins that help clear viruses. Other research shows that omega-3s increase airflow and protect lungs from colds and respiratory infections. In fact, says Somer, DHA and EPA (the two main forms of omega-3s) benefit the immune system at the most basic level, enabling cell membranes to efficiently absorb nutrients and remove toxins.

Chicken soup – This cold remedy has been used for centuries — and with good reason. Cysteine, an amino acid released from chicken during cooking, has a chemical structure similar to acetylcysteine, a drug for bronchitis. The soup thins mucus and calms the symptoms of a stuffed-up nose and wracking cough. A study published in Chest found that even most supermarket brands helped block the inflammatory cells, leading to reduced cold symptoms. Added spices, such as garlic and onions, can increase soup’s immune-boosting power. Have a bowl whenever you feel crummy.

Garlic –According to a study published in Advances in Therapy, subjects who swallowed a garlic capsule for 12 winter weeks were two-thirds less likely to catch a cold; those who did suffered for 3 1⁄2 days less. Garlic contains infection-fighting compounds, including allicin, a potent bacteria fighter that Somer believes is even more effective in food form.

Wheat germ – One-quarter cup of wheat germ packs nearly half of your day’s requirements for zinc, an essential mineral that helps repair cells and strengthens the immune system. Even a slight deficiency in zinc, which is needed to produce white blood cells, can increase your risk of infection. Sprinkle it on your cereal, yogurt, or oatmeal, or add to smoothies.

Pumpkin and sweet potatoes – These foods are rich in vitamin A, which plays a key role in preventing and fighting off infections. Power up your “A” by eating it with zinc-rich foods (carrots for A with pot roast for zinc is a good combo). Not only is zinc immune-boosting in its own right, it’s also necessary for vitamin A to work its magic. Here’s why: Vitamin A can travel through the blood only when it’s bound to a protein. “And zinc is required to make that retinol-binding protein,” says Roberta L. Duyff, RD, author of “American Dietetic Association Complete Food and Nutrition Guide.” “So if you don’t have enough zinc, vitamin A is not going to move from the liver to the tissues, where it does its job.”

Black tea – Drinking five cups a day for two weeks can turn your immune system’s T cells into “Hulk cells” that produce 10 times more interferon, a protein that battles cold and flu infections, according to a Harvard study. Don’t like black tea? The green variety will also do the trick. If you can’t stomach drinking that much, you can still get added protection with fewer cups.

Mushrooms – They contain more than 300 compounds that rev up immunity, in part by escalating the production of infection-fighting white blood cells and making them more aggressive. Shiitake, maitake and reishi varieties contain the most immune-boosting chemicals, but plain old button mushrooms will also do the job.


Soda – A study published in the American Journal of Clinical Nutrition found that eating 100 g of sugar (the equivalent in three cans of soda) significantly hampered the ability of white blood cells to kill bacteria for up to five hours afterward.

That extra glass of alcohol – After a night of too many cocktails, you not only feel lousy — you may also be more susceptible to cold and flu infection. New animal research published in the journal BMC Immunology found that binge drinking suppressed proteins that trigger the release of important infection-fighting cells. Immune system function was down for a full 24 hours after the binge.

Calorie-bomb foods – While it’s hardly shocking that foods packed with fat and calories cause weight gain, it may come as a surprise that being very overweight ups your risk of complications from winter illness. Those who become most seriously ill with swine flu tend to share the same characteristic: a body mass index over 40, meaning they are morbidly obese. Excess weight can cause hormonal imbalances and inflammation that impair the immune system’s ability to fight infection.

Well water – As many as 25 million Americans drink well water that contains more than the safe levels of arsenic determined by the EPA. Arsenic has been linked to several different cancers and affects the immune response to swine flu as well. When researchers from Dartmouth Medical School inoculated two groups of mice with the H1N1 virus, the group that had spent five weeks drinking arsenic-tainted water developed suppressed immune systems, and many died. The mice that didn’t drink the water got the flu but recovered completely.

If your well water tests high, consider switching to bottled water or investing in a remediation system that will remove the arsenic.

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