Immunity
Immunity
A Mighty Defense against Aging
Somewhere in your body, right at this moment, your immune system is choreographing a deadly waltz with viruses, bacteria, fungi and any other unwelcome intruders.
Like a professional dance troupe, a healthy immune system seems to have perfect timing and synchronization. At its best, it is an aggressive age fighter that helps keep you feeling good, looking good and brimming with energy, says Terry Phillips, Ph.D., director of the immunogenetics and immunochemistry laboratories at George Washington University Medical Center in Washington, D.C.
"If the immune system is doing its job, and you have good health, you don't even think about it," Dr. Phillips says. "The best way to keep it that way is to do all the things that are going to keep it naturally strong like exercising, eating right and coping with stress as best you can."
But as we age, our immune system, like an aging dancer, loses some of its dexterity. This incredibly complex defensive system gradually weakens and is less able to pounce on and destroy invading organisms.
"The immune system certainly ages and clearly functions less optimally as we get older. We believe that loss of immune system function is related to the onset of cancer, autoimmune diseases like rheumatoid arthritis and the frequency and severity of infectious diseases. At 27, for example, pneumonia is a nuisance, but at 70 it can be life threatening," says Michael Osband, M.D., adjunct professor at Boston University School of Medicine.
A Look at the All-Star Cast
The immune system actually consists of millions of cells that have many specialized roles. Some play starring roles, while others are stimulated to act only in specific situations. Among the key performers are B-cells and T-cells, which are types of white blood cells. B-cells hang out in the spleen and lymph nodes waiting for specific invaders, also known as antigens. Once a B-cell identifies an invader, it releases antibodies into the bloodstream. These Y-shaped proteins latch on to the antigen and tag it for destruction by various cells.
T-cells mature in the thymus--a small gland in the throat--and are one of the most important parts of the immune system. They are among the few cells in the body that can distinguish normal cells from foes like cancer cells, viruses, fungi and bacteria, says John Marchalonis, Ph.D., professor and chairman of the Department of Microbiology and Immunology at the University of Arizona College of Medicine in Tucson. How T-cells learn to do that is complicated. But basically, on the surface of each T-cell is a receptor, a chemical molecule that recognizes one of the ten million known antigens. So when a T-cell detects an antigen, not only does it seek out and attempt to destroy that intruder, but it also sends out signals to the other parts of the immune system that determine how aggressively the body will attack the invader.
T-cells, for example, can activate macrophages, amoeba-like cells that literally gobble up the intruder or signal the B-cells to crank up their production of antibodies.
A Slow Decline
The immune system reaches its prime just about the time that you enter puberty. Then the thymus begins to wither away, and your T-cell production and function drop considerably. Although you may continue to make T-cells throughout your life, these cells don't identify invaders and choreograph the defensive effort of the immune system as well as the ones produced when the thymus was at its peak, Dr. Osband says. Why the thymus shrinks remains a mystery, but some researchers suspect that the hormones that trigger puberty also may turn off the thymus.
"You generally don't make a lot of T-cells after the thymus goes away. The thymus is important because that's where T-cells learn to recognize antigens," Dr. Osband says. "Clearly, that learning process doesn't stop when the thymus goes, but your T-cells are left to learn on their own. It's like trying to educate yourself by reading an encyclopedia instead of going to college."
Genetics and free radicals--chemically unstable oxygen molecules that cause havoc through the body--also contribute to the decline of the immune system, says Marguerite Kay, M.D., professor of microbiology and immunology at the University of Arizona College of Medicine.
In addition, some invaders like HIV (human immunodeficiency virus), the virus that causes AIDS, attack the immune system directly and destroy it.
Keeping Your Immunity Strong
While some declines in immune power may be a natural part of aging, researchers including Dr. Phillips say that making just a few lifestyle changes can keep your immunity vigilant long into your life. "In the end," Dr. Phillips says, "it's how well we look after ourselves that decides how well our immune systems look after us." Here are some ways to boost your body's natural defenses.
Soothe stress. Researchers have long suspected that stress suppresses the immune system, and emerging evidence supports that theory.
Researchers at Carnegie Mellon University in Pittsburgh, for example, gave cold viruses in the form of nasal drops to 400 volunteers. Placebo drops were given to 26 subjects. The researchers then identified stress levels in both groups and watched for new infections. The highly stressed volunteers ended up being twice as likely to develop colds as the low-stressed volunteers. None of the 26 people who received the placebo got a cold.
Scientists believe that steroids produced by the adrenal glands are released during stress and suppress the activity of immune system cells, Dr. Phillips says.
How you ease stress is an individual choice, but for starters, you could play with your kids or pet, participate in a hobby like gardening or woodworking, do meditation or yoga, watch a funny movie or television program or just read an enjoyable book.
Get some Zzzs. "Sleep is the repair shop for the immune system," Dr. Phillips says. During sleep, your brain and body rest but your immune system doesn't. So when you're snoozing, your immune system has less competition for the nutrients needed to strengthen your disease-fighting mechanisms. Without enough rest, your immune system will suffer. In a study of 23 people, for example, researchers at the University of California, San Diego, School of Medicine found a 30 percent decrease in immune response after these people missed three or more hours of sleep in a night.
Try to get at least six to eight hours of sleep a night, Dr. Phillips suggests.
Stop smoking. Tobacco smoke contains formaldehyde, a chemical that can paralyze macrophages in the lungs and make you more susceptible to upper respiratory ailments, including colds and flus, Dr. Phillips says. So if you smoke, quit.
Sweat it out. Moderate exercise helps prevent bacteria from gathering in the lungs and strengthens the vigilance of the immune system by increasing circulation of antibodies in the blood, says William H. Adler, M.D., chief of clinical immunology at the National Institute on Aging in Baltimore.
After a 15-week study of 18 women in their thirties who were asked to walk 45 minutes a day, five days a week, researchers at Appalachian State University in Boon, North Carolina, found that the walkers had half as many colds and flus as a group of sedentary women.
To keep your immune system at its best, do aerobic exercise like walking, jogging, swimming or bicycling at least 20 minutes a day as often as possible.
Shoot Down the Sniffles Your immune system is tough, but every year you seem to attract the attention of the latest version of the flu bug. Yet all it takes to protect most people against the illness is a shot. In fact, an annual flu vaccination is probably the best health deal in town, says William H. Adler, M.D., chief of clinical immunology at the National Institute on Aging in Baltimore. Don't wait to get immunized until everyone around you is hacking and coughing. That may be too late, since it takes at least two weeks for the vaccination to completely kick in. If possible, get your shot by early October. About one-third of the people who are vaccinated will still get the flu, though usually a much milder case than if they weren't protected at all. Expect to pay between $10 and $15. At some doctors' offices, you don't even need an appointment; you can just walk in and a nurse will administer the vaccine on the spot. |
Eat, Drink and Be Immune
"The role of diet in immunity is very direct," says Jeffrey Blumberg, Ph.D., associate director of the U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University in Boston. "Specific nutrients play very particular roles in pushing immunity up and down."
Here's an A-to-zinc guide to some vitamins and minerals that could help keep your immunity in high gear.
Get on the A list. Vitamin A fortifies the top layer of skin against cracks through which invaders can enter and fights cancer tumors, possibly by boosting white blood cell activity. But since too much vitamin A can be toxic, it's probably a good idea to get your daily requirements from food rather than high-dose supplements, says Ranjit Chandra, M.D., research professor at Memorial University of Newfoundland in St. John's and director of the World Health Organization Center for Nutritional Immunology. The Recommended Dietary Allowance (RDA) is 800 micrograms retinol equivalents (or 4,000 IU). One medium sweet potato has more than double your daily requirement of vitamin A. Other foods rich in vitamin A are liver, carrots, spinach, broccoli, lettuce, apricots and watermelon.
Boost your beta-carotene. An antioxidant, beta-carotene, which is converted to vitamin A in the body, also combats free radicals and may strengthen the immune system's ability to prevent cancer. Like vitamin A, beta-carotene is found in foods such as carrots, spinach, broccoli and lettuce. But, unlike vitamin A, beta-carotene is not toxic and can be taken as a supplement with little danger. Dr. Osband suggests taking six to nine milligrams a day.
Don't forget B6. "When older people were fed diets deficient in vitamin B6, their immunity was lowered substantially," Dr. Blumberg says. "When their intake was then increased one step at a time, immunity gradually returned to normal--but only after intake of more than 1.6 milligrams (the RDA) was provided."
You can get the RDA of 1.6 milligrams of vitamin B6 by eating two large bananas. Other good dietary sources are chicken, fish, liver, rice, avocados, walnuts, wheat germ and sunflower seeds. Vitamin B6 can be toxic in very large doses (1,000 to 2,000 milligrams per day), Dr. Blumberg says.
Supercharge with C. From keeping viruses from multiplying to stimulating tumor-attacking cells, vitamin C gives almost every part of the immune system a boost, Dr. Blumberg says. Fruits and vegetables like oranges, strawberries, broccoli and red bell peppers are good sources of this nutrient. It appears that optimal dosages range from 500 to 1,000 milligrams a day, says Dr. Blumberg.
The sun shines on D. Although scientists know that vitamin D is an immunity booster, they are mystified by its role. They do know that vitamin D is needed for strong bones, which is significant because immune system cells are formed in the bone marrow. Fortunately, most people get their fair share of vitamin D. (The RDA for vitamin D is 5 micrograms or 200 IU a day.) An eight-ounce glass of fortified milk has about 100 IU. It's also abundant in cheeses and oily fish such as herring, tuna and salmon. You can also get vitamin D from sunlight, since ultraviolet radiation triggers a vitamin Dmaking substance in the skin. In summer, about 10 to 15 minutes of sun a day will give you all the vitamin D you need. Vitamin D is toxic in large amounts, so doctors say it should never be taken in supplements.
Eat your E. A real powerhouse, vitamin E can boost your immunity across the board. In particular, it prevents free radical damage to cells, improves white blood cell activity and increases interleukin-2, a substance that promotes the growth of T-cells. It also turns off prostaglandin E2, a naturally occurring substance that suppresses the immune system.
Vitamin E--also considered an antioxidant--can be found in oils, nuts and seeds, but it's difficult to get a health-promoting or immune-boosting dose through food alone, says Dr. Blumberg. Healthy diets generally provide only 20 IU a day. Optimal dosages appear to be between 100 to 400 IU a day, he says.
Ax the fat. In animal studies, a diet consisting of 40 percent of calories from fat--the typical American diet--had a detrimental influence on the immune system, says Dr. Chandra. So try to reduce your fat consumption to 25 percent of calories.
To do it, use low-fat or nonfat dairy products, trim skin or visible fat from meats and eat no more than one three-ounce serving (about the size of a deck of cards) of poultry, fish or red meat a day. Be sure to eat at least six servings of grain products like breads, beans and rice and at least five servings of fruits and vegetables like apples, pears, broccoli and spinach daily.
Pump up your iron. Iron is a vital catalyst that helps your immune system nab intruders and corral renegade cells like cancer. Most women need about 15 milligrams of iron a day. A dinner of a three-ounce broiled lean steak, a medium-size baked potato and a half-cup of peas provides more than seven milligrams. Other iron-rich foods are clams and oysters, pork, dark chicken meat, dried apricots and green leafy vegetables. But don't depend on iron supplements unless they are prescribed by a doctor. Too much iron can cause health problems such as constipation, skin discoloration, cirrhosis of the liver and diabetes.
Maximize your magnesium. Some studies suggest that magnesium deficiency can cause the immune system to run amok, attack normal cells in the body and trigger autoimmune diseases like rheumatoid arthritis, Dr. Phillips says. Taking a magnesium supplement may be a good idea for women on water pills (diuretics) or high blood pressure drugs. Both make you lose this mineral. So does drinking excessive amounts of alcohol. The rest of us can get the RDA of 280 milligrams without supplements by regularly eating leafy vegetables, potatoes, whole grains, milk and seafood.
Stock up on selenium. This nutrient, an antioxidant that's a known cancer fighter, may be required to fire up your immune system's infection-fighting team. You should be getting plenty in your normal diet. The RDA of selenium for women is 55 micrograms, and you'll get 138 micrograms from a tuna sandwich alone. All fish, shellfish and whole-grain cereals and breads are selenium rich. Very high doses can impair immune responses, however, so supplements should not exceed 200 micrograms a day, Dr. Chandra says.
Try zinc, the missing link. "Of all the minerals, zinc is probably the most important for maintaining immunity," Dr. Phillips says. A shortage can cause a drop in production of the white blood cells that surround and destroy microscopic invaders. Zinc also helps the body process vitamin D, another important nutrient that bolsters immunity. To get the RDA of 12 milligrams from your diet, eat lean red meat, oysters, milk, oats, whole grains, eggs and poultry. Avoid supplements providing more than 40 milligrams, Dr. Blumberg warns. Beyond these levels, zinc can actually slow the immune system down.