What You Eat Could Affect Your Ability to Fight Off Disease
“Excess sugar, refined foods . . . and lack of exercise contribute to immune-system depression,” writes Richard Clark Kaufman in “The Age Reduction System.”
“You can easily eliminate 80% of the risk that you will catch a cold,” promises Norman D. Ford in “Eighteen Natural Ways to Beat the Common Cold.”
Despite the confident claims of these and other immune-boosting manuals, the link between nutrition and immunity is still mysterious.
“Part of the problem is that immunologists have not focused their attention on nutrition, and nutritionists are not trained in immunology,” says David Jacobs, a Washington physician certified in internal medicine, clinical nutrition and immunology.
One obstacle is that there are scores of immune tests, each measuring different components of immune function. Adding or subtracting a single nutrient may make the activity of some components go up, while making others go down.
Translation Difficulty
What’s more, scientists don’t yet know how to translate the various immune tests results into a person’s chances of getting sick. “Each test is like one of the three blind men examining an elephant,” explains Jacobs. “Each evaluates one small part of the animal, but none understands how it all fits into the big picture.”
Composed of about one trillion cells that are regulated by dozens of enzymes, the immune system must be able to correctly recognize a foreign body, multiply, call for reinforcements, destroy the enemy, call off the troops and create “memory” cells.
In a healthy immune system, foreign bodies often meet such a swift death that a battle could be going on as you read this without your experiencing so much as a sniffle.
But a depressed immune system may fail to recognize an invader, or fail to mount a vigorous attack. The result can be recurrent, severe or exotic infections, or even a life-threatening cancer. “Poor immune function can produce a susceptibility to the formation of tumors,” says Susanna Cunningham-Rundles of Cornell University Medical Center.
Immune cells need protein, vitamins, minerals and some essential fatty acids to launch their elaborate defense.
‘Primary Evidence’
“The primary evidence for the role of nutrients in the regulation of the immune system comes from serious deficiency diseases where there is a terrible compromise in immunity,” says Jeffrey Blumberg of the USDA Nutrition Center at Tufts University.
Severe malnutrition is not common in this country. But some segments of the population, such as older people, are still at nutritional risk.
“The elderly are more susceptible to infection, their response is more severe and it takes them longer to recover. Most of this may be due to less-than-vigorous immune systems,” says Blumberg.
Like other systems, immunity declines with age, so nutrient deficiencies may not completely explain why older people often have difficulty fighting infection, but poor nutrition may play a role.
In a study done at Memorial University of Newfoundland, Ranjit K. Chandra and co-workers found evidence of both nutrient deficiencies and a depressed immune response in 21 volunteers over the age of 60. They scored better on several immune tests after 8 weeks of consuming an extra 500 calories a day of Ensure, a liquid supplement containing protein, fat, carbohydrates, vitamins and minerals.
While the patients in Chandra’s studies showed clear signs of nutrient deficiencies (including iron-deficiency anemia, weight loss and low blood protein or zinc levels), researchers suspect that many people who appear healthy may also have impaired immunity.
“Subclinical nutrient deficiencies can also depress the immune system,” Blumberg pointed out. In other words, apparently healthy people may have such slight nutrient deficiencies that they show up only after special blood tests and careful diet histories.
It is hard to study subclinical deficiencies in people. But here is what researchers have learned about just a few of the nutrients that affect immunity.
Beta-Carotene. Forget an apple a day. Maybe it is cantaloupe, carrots, butternut squash and broccoli that keep the doctors away. Beta-carotene, the precursor of Vitamin A found in many green and yellow fruits and vegetables, seems to play a role in immunity.
Michael Alexander and colleagues at the University of Toronto gave a daily dose of 180 milligrams of beta-carotene to 10 men ages 20 to 40 for 2 weeks. Compared to seven men who received a placebo, the beta-carotene takers showed an increase in helper T cells, sometimes called the “battle managers” of the immune system.
Because the AIDS virus depletes helper T cells, the authors conclude, “our data suggest that beta-carotene administration might be considered for patients with AIDS.” Yet that suggestion is described as “wildly speculative” by others. “I don’t think you can extrapolate from nutrient effects on normal immunity to nutrient effects on an aberrant immune system--AIDS--in which a number of immune system elements are totally altered,” Blumberg says.
Vitamin B-6. Many Americans--particularly older people--get less-than-recommended levels of Vitamin B-6. And frank Vitamin B-6 deficiencies definitely impair the immune system.
In a study at Oregon State University in Corvallis, researchers gave a daily dose of 50 milligrams of Vitamin B-6 (25 times the USRDA) to a small group of volunteers ages 65 to 81. Half had low B-6 levels at the outset.
After 2 months, those people who were initially low in the vitamin scored better on four immune tests. Even the initially normal subjects did better on two tests.
But the study’s authors are cautious. “We cannot recommend taking B-6 supplements for the immune system,” researcher Lorraine Miller says. “Our study was only for 2 months, so the effect may be transient.
“We’re also concerned about potential toxicity at these levels, though 50 milligrams would not cause the nerve damage associated with higher levels of B-6,” Miller continues. “Our future studies will be longer, and will use only 10 milligrams of B-6.”
Vitamin C. Probably the most popular immune-enhancing nutrient is Vitamin C. A recent study suggests that this practice may be based on more than just folk wisdom.
Elliot Dick and associates at the University of Wisconsin gave eight men 500 milligrams of Vitamin C four times a day for 3 1/2 weeks. The other eight men got a placebo.
For the next week, all 16 lived in the same dormitory as a group of cold-carriers, each of whom had been intentionally infected with the same cold virus. The men engaged in “supervised interactive activities” with the carriers. (In other words, they played poker.) Then the men went home, but continued taking their pills--either Vitamin C or placebo--for the next two weeks.
The results were clear: While Vitamin C didn’t keep the men from catching colds, it did make the cold’s symptoms--especially coughs--about half as severe.
Vitamin E. “Our studies have shown that even with an optimal diet, extra Vitamin E improved immune function. T and B cell function may require more Vitamin E than other cells,” says Adrianne Bendich, a research scientist with Hoffmann-La Roche, the largest vitamin manufacturer in the United States.
Bendich’s studies--conducted on animals--are interesting. But the studies have not shown that high doses of Vitamin E prevent illness in humans.
Indeed, studies on humans are less clear-cut. Researchers at the University of Nebraska gave a daily dose of 0, 200 or 400 milligrams of Vitamin E (7 to 13 times the USRDA) to 103 young and old patients in a chronic-care facility. The Vitamin E takers showed no better immune response to a flu vaccine and no fewer infections over the next 4 months.
Still, the Nebraska study doesn’t close the book on Vitamin E. Simin Meydani of the USDA Nutrition Center at Tufts University finds the animal studies so compelling that she is currently testing 800 milligrams of Vitamin E on humans.
“The studies indicate that those animals with infections plus extra Vitamin E have decreased mortality compared to animals with infections fed only adequate Vitamin E,” Meydani says. “There appears to be a positive immune effect.”
Zinc. The evidence on zinc and the immune system is mixed.
In one study, taking 300 milligrams (20 times the USRDA for zinc) for 6 weeks actually impaired some components of the immune system in 12 healthy men.
In another study, taking megadoses of up to 150 milligrams of zinc (10 times the USRDA) decreased other components of the immune response in 83 healthy people who started out with better-than-average immunity. But the same dose boosted immunity in volunteers who had the weakest immune function to start.
Critics of these and other studies noted that there were too few participants and that they did not measure actual blood zinc levels. What’s more, all the participants knew they were getting zinc and some studies did not give placebos to a control group for comparison.
Rather than megadoses, just the USRDA for zinc may be enough to boost a faltering immune system--if it is combined with other trace elements.
Researchers at the San Diego Veterans Administration Medical Center and UC San Diego gave 17 men and women ages 66 to 85 either seven times the USRDA for zinc, or a multi-mineral supplement that supplied just the USRDA for zinc, copper, iron and manganese.
Both groups showed some improvement in B cell and T cell function. However, only the multi-mineral-fed group had an increase in one of the many enzymes necessary for immune function.
One of the investigators, William Hollingsworth at the San Diego VA Medical Center, said: “My own bias is to take a multi-mineral supplement because the trace minerals may be interacting in some way. Too much zinc may suppress immunity.”
While too few nutrients may throw a wrench into the immune system, some types of leanness may confer immune protection.
In studies conducted by Richard Weindruch of the National Institute on Aging, animals fed 50% fewer calories had stronger immune systems and a lower incidence of disease compared to those fed a normal number of calories. The little food the animals did get was nutrient-packed, so they didn’t become deficient in vitamins, minerals or protein.
Weindruch believes that calorie restriction may help preserve certain components of the immune system. He thinks it may also slow the aging of the thymus gland, which regulates T-cell maturation.
When animals are fed diets rich in fat--especially a polyunsaturated vegetable fat such as safflower oil--their immune systems are weaker than those of animals fed only tiny amounts of these fats.
Michael Bennett and colleagues at the University of Texas Southwestern Medical Center found that mice fed 30% of their calories from a monounsaturated oil had good responses on most though not all immune tests. In contrast, mice fed polyunsaturated safflower oil did poorly on most tests.
But people can take heart from one consistent result: Animals fed a low-fat diet (16% of calories from fat) had a perfectly normal immune response, no matter whether the fat was polyunsaturated safflower or highly saturated coconut oil. Still, some researchers hesitate to apply the results of these animals studies to humans.
“There is no evidence in free-living humans that polyunsaturated fat or any fat, for that matter, depresses immunity,” says Joseph Vitale of Boston University School of Medicine. “(The animal studies) represent an artificial situation. We don’t eat bowls of corn oil.”
Indeed, while 30 to 40% of the calories in the animals’ diets in several studies came from a polyunsaturated vegetable oil, the average American gets only about 7% of his or her calories from those fats.
Animal studies can’t provide absolute proof, but they can’t be dismissed, either. For the cautious eater, the results of animal studies on fats and immunity provide one more reason to use monounsaturated olive oil for cooking.
Preliminary results do suggest that diet may help strengthen our defense forces. Perhaps the best advice is to:
Eat a diet low in fat. For cooking and baking, use small amounts of olive oil.
Eat fruits and vegetables rich in beta-carotene and Vitamin C.
Try taking extra Vitamin C when you get a cold. By the time you have the cold, it may be too late, but then again, it may not. (Do not take chewable tablets. They erode tooth enamel.)
If you usually eat no more than about 1,600 calories a day, take an inexpensive multi-vitamin, multi-mineral supplement that supplies 100% of the USRDA for zinc, iron, copper and manganese.
These tips won’t provide sure-fire protection, but they can’t hurt. Whether they actually help fight infection, only the future will tell.
