You Asked for It: Question Authority

Nieman, David C. Dr.P.H., FACSM

ACSM'S Health & Fitness Journal:
doi: 10.1249/FIT.0b013e3181e37d73
DEPARTMENTS: You Asked For It: Question Authority
In Brief

Is it possible to "feed" and "exercise" your immune system and "boost" its fighting power, as is so often claimed?

Author Information

David C. Nieman, Dr.P.H., FACSM, is professor and director of the Human Performance Laboratory, Appalachian State University, in Boone, North Carolina, an active researcher; and author of several textbooks on health and fitness. Send your questions

Article Outline


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A:I think the concept of "boosting immune function" through diet and exercise is erroneous. What we do know is that a healthy lifestyle "supports" normal immunity, and that poor habits of living impair immune function.

From birth, we are exposed to a continuous onslaught of bacteria, viruses, and other disease-causing organisms that are collectively called pathogens. Without an effective shield, we would soon succumb to infectious disease and cancer. Fortunately, protection is delivered through a complex array of barriers, cells, and molecules that together form the immune system.

Lifestyle habits are strongly related to immune function. For example, whether you get sick with the common cold after a sufficient amount of virus has entered your body depends on many factors that affect the immune system. Old age, avoidance of physical activity, mental stress, poor nutrient and energy status, and lack of sleep have all been associated with impaired immune function and elevated risk of infection.

One of the best ways to reduce sick days is through near-daily physical activity. During moderate-to-vigorous exercise (e.g., brisk walking, cycling, swimming, sports play), several positive changes occur in the immune system (6). These include a transient increase in the recirculation of neutrophils, natural killer cells, and immunoglobulins, improving the immune system's ability to detect and kill pathogens. Stress hormones, which can suppress immunity, and inflammatory cytokines, indicative of physiological stress, are not elevated during moderate exercise. Although components of the immune system return to preexercise levels within a few hours after the exercise session is over, each session represents an improvement in surveillance against pathogens that reduces the risk of infection.

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Thus, over time, regular moderate physical activity translates to fewer days of sickness with the common cold and other upper respiratory tract infections (1). The 25% to 50% reduction in sick days with near-daily moderate exercise reported in most studies exceeds levels associated with use of medications and supplements and bolsters public health guidelines urging individuals to be physically active on a regular basis.

Heavy doses of exercise, however, can have the opposite effect. For example, after running a marathon race, the body is inflamed for about one-half day with high stress hormones, cytokines, and suboptimal immune function. During the ensuing 1 to 2 weeks, the odds of becoming sick increase twofold to sixfold, depending on the time of year (5). During periods of heavy training, the immune system reflects the physiological stress experienced by the athlete, and illness rates climb. So a good thing - exercise - can be carried too far, and each individual needs to find the right balance between training workloads and rest (Figure).

The elderly gain more immune benefits from physical activity than any other age group. Very old individuals are more susceptible to various infections, autoimmune disorders, and cancers when compared with younger adults. Recent evidence shows that regular physical activity helps counter the typical age-related decrease in immune function, improves the antibody titer response to influenza immunization, and lowers rates of infection from the common cold (4).

Nutrition has a major influence on your immune function, and nearly all nutrients provide support for the immune system in its work against viruses and bacteria. The best studies, however, indicate that a balanced healthy diet provides all the nutrients needed for good immune function in most healthy adults, and vitamin/mineral supplements do not "boost" immunity more than normal levels (8).

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"Boosting immunity" is an attractive notion. In this era of bird flu, H1N1 influenza, acquired immunodeficiency syndrome, and the West Nile virus, more of us are concerned about a healthy immune system than ever before. A wide assortment of herbal and nutritional supplements are available for "bolstering immunity," but most have little or no scientific backing other than a long history of use in Chinese medicine. Unique plant molecules called polyphenols and flavonoids are currently causing much excitement for their potential to support immune function during times of physiological and mental stress, but more research is needed with a variety of human subjects before they can be recommended as efficacious.

Patience is needed with the scientific process as researchers work through simple to more complex research designs. It takes time for the truth to emerge on the usefulness of certain herbals or nutritional components in maintaining immunity. Supplement companies often move ahead with a product based on limited data, make their money from a confused public, drop the supplement when the public loses interest or when strong evidence indicates that it is useless, and then move on to something else. A prime example of this is the Airborne cold remedy, a popular herbal and vitamin formula originally touted as a cold preventive. The Federal Trade Commission ruled in 2008 that there is no evidence that Airborne products "provide any tangible benefit for people who are exposed to germs in crowded places." The makers of Airborne tablets have agreed to pay $30 million to settle a lawsuit and federal regulators' charges that they made false claims about the cold-fighting benefits of the fruit-flavored remedy.

An important lifestyle factor related to immune function and illness rates is mental or psychological stress. High mental stress increases susceptibility to both the common cold and the flu. The likelihood of getting ill is directly linked to the magnitude and duration of stressful events and demeanor (2). During a 6-month period, for example, the number of sick days is twice as great in high- compared with low-stress groups. Immune function is profoundly influenced by the presence of stress hormones induced by mental stress.

Sleep disruption also impairs immune function. For example, the antibody response to the flu shot is reduced in individuals experiencing sustained sleep debt (7). In cold-virus challenge studies, subjects with a history of poor sleep quality were more prone to illness (3). High mental stress and sleep disruption typically coexist, a one-two punch that brings down immunity, allowing viruses to gain control.

We live in a world where viruses and bacteria are omnipresent, waiting to pounce on any of us with weakened immune systems. Your best strategy is to keep immune defenses operating normally by following a variety of lifestyle habits, as described in this article:

▸ Exercise moderately on most days of the week. This will improve the ability of the immune system to detect and destroy viruses and bacteria.

▸ Avoid overtraining and chronic fatigue. Heavy exertion causes immune dysfunction in multiple body compartments, leading to an increased risk of illness. Another word of caution: do not exercise when ill with a fever. This can lead to more severe symptoms, relapse, and sustained feelings of fatigue.

▸ Eat a well-balanced diet to keep vitamin and mineral pools in the body at optimal levels. Nutrient supplements are typically not needed by healthy adults and will not boost immune function more than normal levels.

▸ Keep life stresses to a minimum, and practice stress management techniques. Mental stress increases the risk of the common cold, so learn to control the burden and pace of life.

▸ Obtain adequate sleep on a regular schedule. Sleep disruption has been linked to suppressed immunity.

▸ You also can limit exposure to viruses and bacteria by practicing good hygiene. Wash your hands frequently and avoid touching your eyes and nose (the primary routes of introducing viruses into the body). In addition, give your immune system an edge by receiving the flu shot and other recommended vaccinations each and every year.

Overall, a well-rounded lifestyle based on healthy eating habits, regular physical activity, stress management, and proper rest promotes good immune function and lowers the risk of infectious illness.

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© 2010 American College of Sports Medicine.