Do you ever suffer from colds or flu and wonder if and when it is appropriate to continue to exercise or what you should eat to give your body the best chance to recover from periods of illness?

Nutrition and exercise can play an important role in combatting colds and infections.

Nutrition for Your Immune System

As mentioned in ‘Fighting Infection: Your Body’s Natural Defences’, for an infection which is entering the body for the first time, it can take up to 2-3 weeks for the body to mount an appropriate defence. During prolonged periods of intense exercise where the body is continually having to replenish tired muscle tissue and dispose of waste products, additional nutrition is required to support the production of T cells and antibodies required to fight the infection.



For example, one group of investigators has found that in mice, diets deficient in protein reduce both the numbers and function of T cells and macrophages and also reduce the production of immunoglobulin A (IgA) antibody.

Researchers have found that each of the following are important in maintaining a heathy immune system:

Selenium. Some studies have suggested that people with low selenium levels are at greater risk of bladder, breast, colon, rectum, lung, and prostate cancers. A large-scale, multiyear study is currently in progress to look at the effects of combining selenium and vitamin E on prostate cancer prevention.

Vitamin A. Experts have long known that vitamin A plays a role in infection and maintaining mucosal surfaces by influencing certain subcategories of T cells and B cells and cytokines. Vitamin A deficiency is associated with impaired immunity and increased risk of infectious disease. On the other hand, according to one study, supplementation in the absence of a deficiency didn’t enhance or suppress T cell immunity in a group of healthy seniors.

Vitamin B2. There is some evidence that vitamin B2 enhances resistance to bacterial infections in mice, but what that means in terms of enhancing immune response is unclear.
Vitamin B6. Several studies have suggested that a vitamin B6 deficiency can depress aspects of the immune response, such as lymphocytes’ ability to mature and spin off into various types of T and B cells. Supplementing with moderate doses to address the deficiency restores immune function, but megadoses don’t produce additional benefits. And B6 may promote the growth of tumors.

Vitamin C. The effects of vitamin C on the immune system remain unclear. Many studies have looked at vitamin C in general; unfortunately, many of them were not well designed. Vitamin C may work in concert with other micronutrients rather than providing benefits alone.

Vitamin D. For many years doctors have known that people afflicted with tuberculosis responded well to sunlight. An explanation may now be at hand. Researchers have found that vitamin D, which is produced by the skin when exposed to sunlight, signals an antimicrobial response to the bacterium responsible for tuberculosis, Mycobacterium tuberculosis. Whether vitamin D has similar ability to fight off other diseases and whether taking vitamin D in supplement form is beneficial are questions that need to be resolved with further study.

Vitamin E. A study involving healthy subjects over age 65 has shown that increasing the daily dose of vitamin E from the recommended dietary allowance (RDA) of 30 mg to 200 mg increased antibody responses to hepatitis B and tetanus after vaccination. But these increased responses didn’t happen following administration of diphtheria and pneumococcal vaccines.

Zinc. Zinc is a trace element essential for cells of the immune system, and zinc deficiency affects the ability of T cells and other immune cells to function as they should. Caution: While it’s important to have sufficient zinc in your diet (15–25 mg per day), too much zinc can inhibit the function of the immune system.

Scientists have looked at a number of herbs and vitamins in terms of their potential to influence the immune system in some way. Much of this research has focused on the elderly, children, or people with compromised immune systems, such as AIDS patients. Many of the studies were later found to have design flaws, which means further studies are needed to confirm or disprove the results. Consequently, these findings should not be considered universally applicable.

Some of the supplements that have drawn attention from researchers are these:

Aloe vera. For now, there’s no evidence that aloe vera can modulate immune response. Because many different formulations and compounds have been used in studies, comparing the results is difficult. However, there is some evidence that topical aloe vera is helpful for minor burns, wounds, or frostbite, and also for skin inflammations when combined with hydrocortisone. Studies have found aloe vera is not the best option for treating breast tissue after radiation therapy.

Astragalus membranes. The astragalus product, which is derived from the root of the plant, is marketed as an immune-system stimulant, but the quality of the studies demonstrating the immune-stimulating properties of astragalus are poor. Furthermore, it may be dangerous.

Echinacea. An ocean of ink has been spilled extolling echinacea as an “immune stimulant,” usually in terms of its purported ability to prevent or limit the severity of colds. Most experts don’t recommend taking echinacea on a long-term basis to prevent colds. A group of physicians from Harvard Medical School notes that studies looking at the cold prevention capabilities of echinacea have not been well designed, and other claims regarding echinacea are as yet not proven.

Echinacea can also cause potentially serious side effects. People with ragweed allergies are more likely to have a reaction to echinacea, and there have been cases of anaphylactic shock. Injected echinacea in particular has caused severe reactions. A well-designed study by pediatricians at the University of Washington in Seattle found echinacea didn’t help with the duration and severity of cold symptoms in a group of children. A large 2005 study of 437 volunteers also found that echinacea didn’t affect the rate of cold infections or the progress and severity of a cold.

Garlic. Garlic may have some infection-fighting capability. In laboratory tests, researchers have seen garlic work against bacteria, viruses, and fungi. Although this is promising, there haven’t been enough well-designed human studies conducted to know whether this translates into human benefits. One 2006 study that looked at rates for certain cancers and garlic and onion consumption in southern European populations found an association between the frequency of use of garlic and onions and a lower risk of some common cancers. Until more is known, however, it’s too early to recommend garlic as a way of treating or preventing infections or controlling cancer.

Ginseng. It’s not clear how the root of the ginseng plant works, but claims on behalf of Asian ginseng are many, including its ability to stimulate immune function. Despite the claims of a number of mainly small studies, the National Center for Complementary and Alternative Medicine (NCCAM) considers there have been insufficient large studies of a high enough quality to support the claims. NCCAM is currently supporting research to understand Asian ginseng more fully.

Glycyrrhiza glabra (licorice root). Licorice root is used in Chinese medicine to treat a variety of illnesses. Most studies of licorice root have been done in combination with other herbs, so it’s not possible to verify whether any effects were attributable to licorice root per se. Because of the potential side effects of taking licorice and how little is known about its benefits — if any — for stimulating immune function, this is an herb to avoid.

Probiotics. There are hundreds of different species of bacteria in your digestive tract, which do an effective job of helping you digest your food. Now researchers, including some at Harvard Medical School, are finding evidence of a relationship between such “good” bacteria and the immune system. For instance, it is now known that certain bacteria in the gut influence the development of aspects of the immune system, such as correcting deficiencies and increasing the numbers of certain T cells. Precisely how the bacteria interact with the immune system components isn’t known. As more and more intriguing evidence comes in to support the link that intestinal bacteria bolster the immune system, it’s tempting to think that more good bacteria would be better. At least, this is what many marketers would like you to believe as they tout their probiotic products.

Probiotics are good bacteria, such as Lactobacillus and Bifidobacterium, that can safely dwell in your digestive tract. You’ll now find probiotics listed on the labels of dairy products, drinks, cereals, energy bars, and other foods. Ingredients touted as “prebiotics,” which claim to be nutrients that feed the good bacteria, are also cropping up in commercially marketed foods. Unfortunately, the direct connection between taking these products and improving immune function has not yet been made. Nor has science shown whether taking probiotics will replenish the good bacteria that get knocked out together with “bad” bacteria when you take antibiotics.

Another caution is that the quality of probiotic products is not consistent. Some contain what they say they do; some do not. In a 2006 report, the American Academy of Microbiology said that “at present, the quality of probiotics available to consumers in food products around the world is unreliable.” In the same vein, the FDA monitors food packages to make sure they don’t carry labels that claim the products can cure diseases unless the companies have scientific evidence to support the claims. Does this mean taking probiotics is useless? No. It means further research is required to support the expansive health claims. In the meantime, if you choose to take a probiotic in moderation, it probably won’t hurt, and the scientific evidence may ultimately show some benefit.

Exercise and Your Immune System

Regular exercise is one of the pillars of healthy living. It improves cardiovascular health, lowers blood pressure, helps control body weight, and protects against a variety of diseases. But does it help maintain a healthy immune system? Just like a healthy diet, exercise can contribute to general good health and therefore to a healthy immune system. It may contribute even more directly by promoting good circulation, which allows the cells and substances of the immune system to move through the body freely and do their job efficiently.

Some scientists are trying to take the next step to determine whether exercise directly affects a person’s susceptibility to infection. For example, some researchers are looking at whether extreme amounts of intensive exercise can cause athletes to get sick more often or somehow impairs their immune function. To do this sort of research, exercise scientists typically ask athletes to exercise intensively; the scientists test their blood and urine before and after the exercise to detect any changes in immune system components such as cytokines, white blood cells, and certain antibodies. While some changes have been recorded, immunologists do not yet know what these changes mean in terms of human immune response. No one yet knows, for example, whether an increase in cytokines is helpful or has any true effect on immune response. Similarly, no one knows whether a general increase in white cell count is a good thing or a bad thing.

But these subjects are elite athletes undergoing intense physical exertion. What about moderate exercise for average people? Does it help keep the immune system healthy? For now, even though a direct beneficial link hasn’t been established, it’s reasonable to consider moderate regular exercise to be a beneficial arrow in the quiver of healthy living, a potentially important means for keeping your immune system healthy along with the rest of your body.

It is not known exactly if or how exercise increases your immunity to certain illnesses, but there are several theories such that:

• Physical activity may help flush bacteria out of the lungs and airways. This may reduce your chance of getting a cold, flu, or other airborne illness.

• Exercise causes changes in antibodies and white blood cells. These antibodies or white blood cells circulate more rapidly, so they could detect illnesses earlier than they might have before. However, no one knows whether these changes help prevent infections.

• The brief rise in body temperature during and right after exercise may prevent bacteria from growing. This temperature rise may help the body fight infection more effectively.

• Exercise slows down the release of stress-related hormones. Some stress increases the chance of illness. Lower stress hormones may protect against illness.

Although exercise is good for you, be careful not to overdo it. People who already exercise regularly should not exercise more intensely just to increase their immunity. Heavy, long-term exercise (such as marathon running and intense gym training) could actually decrease the amount of white blood cells circulating through the body and increase stress-related hormones.

Further, it’s typically safe to exercise at a low intensity if you have “above-the-neck” symptoms (runny nose, sneezing, sore throat). If those symptoms diminish during the first few minutes of exercise, the intensity may be increased. Exercise isn’t recommended for people with “below-the-neck” symptoms (fever, sore muscles or joints, vomiting, diarrhea, or a cough that produces mucous). If you have those symptoms, let the cold run its course before you resume physical activity.

General advice is to wait two weeks after symptoms subside before engaging in intensive training. When you do return to training, allow two days of below-normal exercise intensity for each day you were sick before jumping back into your normal training routine.

Exercise can help you feel better about yourself, just by making you feel healthier and more energetic. So go ahead, take that aerobics class or go for that walk. You’ll feel better and healthier for it.

Marc DinardoWritten by Marc Dinardo

REPS Level 3 Personal Trainer
ASA Level 2 Swim Instructor
Diploma in Swedish Massage