Smart Diet Bolsters Immune System To Fend Off Gate-Crashing Germs

With every breath you take and bite of food you eat, potentially hazardous viruses and bacteria go along for the ride. But the human body doesn't welcome these hitchhikers. It wields an arsenal of defenses--the immune system--to ward off intruders.

Some factors (age, genetics) that influence how well your immune system responds to gate-crashers are out of your control. But researchers are finding that the nutrients you eat have a powerful effect on immunity. For example, vitamin A is key to maintaining the protective barriers that line the mouth, lungs and intestines and filter out marauding microbes.

How Much Is Enough? Research shows you don't need megadoses of vitamins and minerals to maintain a well-functioning immune system. Simply meeting recommended levels for most nutrients may be enough. In fact, excesses of some nutrients, especially minerals, can be harmful. For example, excessive iron can exacerbate the infectious process as much as too little. Likewise for copper. Too much copper creates nasty free radicals in cell membranes, causing DNA damage.

Even zinc--the nutrient of the hour for fending off colds--can be too much of a good thing in large amounts. Too much zinc can deplete the body of copper, suppressing immunity.

A varied diet is the ideal way to ensure the correct balance of nutrients for optimal immune functioning. At least one study, however, has shown that a daily multivitamin/mineral can boost immune function, especially if your diet is less than optimal to start.

Can Vitamin E Keep You Flu-Free? Of all the nutrients being studied, vitamin E shows the most promise as a single supplement. A recent study of 80 healthy older people found that supplementing with E improved immunity. Volunteers supplementing with the vitamin reported fewer infections than those receiving a placebo.

Simin N. Meydani, Ph.D., of the Human Nutrition Research Center on Aging at Tufts University in Boston, found that 200 milligrams of vitamin E was the optimal amount to produce a positive immune response. Higher doses provided no further benefit.

Which Fat Fights Infection? If there is a downside to the current craze of extremely-low-fat diets, it may be impaired immune function, say some experts. Because the body cannot make them, we need to ingest small amounts of two essential fatty acids: linoleic acid (an omega-6 fat found in most vegetable oils and margarines) and alpha-linolenic acid (an omega-3 fat found in fish, flaxseed, walnuts and canola oil). Not getting enough of these essential fats can delay wound healing, one measure of immune function. The average American has no trouble getting omega-6's. It's our omega-3 intake that could use a boost.

EN Sums Up. Keeping your immune system in tip-top working order does not require Herculean efforts, or even scads of supplements. (Perhaps just a basic multivitamin/mineral and a vitamin E supplement.) A lifetime of intelligent eating undoubtedly provides the base to build on and is a logical place to start.

EN's Blueprint for a Strong Immune System
Eat a wide variety of foods. Include five to nine servings of fruits and vegetables daily, plus whole grains, lean protein, nonfat dairy foods and small amounts of nuts and seeds.
Include fish in your diet weekly.
Keep fat intake below 30% of calories. Limit margarine. Go easy on corn, safflower, sunflower and soybean oils. Use olive and canola oils primarily.
Take a multivitamin/mineral supplement that provides 100% of the Daily Value for most nutrients, particularly B vitamins and minerals, which are harder to get from foods.
Consider a vitamin E supplement (200 IU of natural source mixed tocopherols or 300 to 400 IU of synthetic).
Glossary
B cells--Plasma cells, which produce antibodies, and memory cells, which recognize organisms in subsequent attacks.

Immunoglobulins--Antibodies that first recognize and destroy foreign invaders.

Lymphocytes--White blood cells that include B and T cells.

Neutrophils--A type of leukocyte that combats infection by scavenging bacteria.

T cells--T helper cells. T killer cells and suppressor T cells, which directly kill pathogens or work via assistants called cytokines, including interleukin, interferon and tumor necrosis factor.

Thymus--A gland essential to the production of mature T cells.

Key Nutrient-Immune System Links
Legend for Chart:

A - Nutrient
B - Immune Defense Affected
C - Getting the Right Amount

A B C

Protein Immunoglobulins Eat legumes or
small servings of
lean meat, chicken
and fish.

Omega-6 fats Wound healing, T cells Eat corn,
safflower, soybean
and sunflower
oils, but in small
amounts only.
Limit margarine.

Omega-3 fats Wound healing, Eat fish at least
inflammation once a week.
Eat walnuts,
flaxseed oil and
canola oil, in
moderation.

Vitamin A and Mucous membranes, Eat deep yellow,
carotenoids lymphocytes orange, red and
green veggies.

B Vitamins Antibodies, leukocytes Eat dark leafy
(riboflavin, greens, bananas,
folate, B6, B12) legumes,
wholegrains, low-fat milk,
lean meats. Take a
multivitamin/
mineral with 100%
of Daily Values.

Vitamin C B cells Eat citrus fruits,
T cells tomatoes,
strawberries,
broccoli,
cauliflower
and dark leafy
greens.

Vitamin E Antibodies, Take 200 IU of
antioxidants natural-source
vitamin E
(for 300-400 IU
synthetic E).

Copper T cells, neutrophils Eat beans, whole
grains, apricots
and potatoes. Take
a daily
multivitamin/
mineral.

Iron Lymphocytes Eat small amounts
of lean meats or
take a daily
multivitamin/
mineral (limited to
10 milligrams of
iron if
post-menopausal or
male).

Zinc Thymus, T cells Eat beans, wheat
germ, whole grains,
lean beef and
turkey. Take a
daily multivitamin/
mineral.
(C) Copyright, 1998 by Environmental Nutrition, Inc., 52 Riverside Drive, New York, NY 10024

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By Catherine Golub, M.S., R.D.

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