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The immune system is an intricate network of specialized tissues, organs, cells, and chemicals. The lymph nodes, spleen, bone marrow, thymus gland, and tonsils all play a role, as do lymphocytes (specialized white blood cells), antibodies, and interferon.
Two types of immunity protect the body: innate and adaptive. Innate immunity is present at birth and provides the first barrier against microorganisms. The skin, mucus secretions, and the acidity of the stomach are examples of innate immunity that act as barriers to keep unwanted germs away from more vulnerable tissues.
Adaptive immunity is the second barrier to infection. It is acquired later in life, such as after an immunization or successfully fighting off an infection. The adaptive immune system retains a memory of all the invaders it has faced. This is why people usually get the measles only once, although they may be repeatedly exposed to the disease. Unfortunately some bugs—such as the viruses that cause the common cold—“disguise” themselves and must be fought off time and again by the immune system.
Symptoms of decreased immune function include frequent colds and flus, recurring parasitic infections, initially mild infections that become serious, opportunistic infections (infections by organisms that are usually well controlled by a healthy immune system, such as toxoplasmosis, cryptococcosis, and cytomegalovirus), and cancer.
Both excessive thinness and severe obesity are associated with impaired immune responses.1 Obesity increases the risk of infection, at least in hospitalized patients, according to preliminary research.2 However, these effects may not occur with mild to moderate obesity in otherwise healthy people, and attempts to lose weight through dietary restriction may actually be harmful to the immune system.3 The detrimental effects of both appear to be offset when people regularly perform aerobic exercise.4, 5
The effects of exercise on immune function depend on many factors, including frequency and intensity of exercise.6 Regular moderate physical activity has positive effects, at least on some measures of immunity, and has been shown to reduce risk of upper respiratory infection. However, very intense and prolonged exercise, such as running a marathon or overtraining, can, in the short term, actually increase the risk of developing infections.7 The positive effects of moderate exercise on immunity may also partly explain the apparent reduced susceptibility to cancer of physically active people.8
The immune system is suppressed during times of stress. Chronic mental and emotional stress can reduce immune function, but whether this effect is sufficient to increase the risk of infection or cancer is less clear.9, 10 Nevertheless, immune function has been increased by stress-reducing techniques such as relaxation exercises, biofeedback, and other approaches,11, 12 although not all studies have shown a significant effect.13
Copyright © 2016 Healthnotes, Inc. All rights reserved. www.healthnotes.com
The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2017.