The immune system is the body's natural defense mechanism against disease-causing microbes, including bacteria, viruses, parasites, or fungi. The immune system also defends the body against harmful chemicals and other toxins that may enter the body through environmental exposure.
The immune system comprises a network of white blood cells, tissues, and organs that work together throughout the body to prevent disease-causing agents from entering the body and to attack and destroy foreign organisms after they have entered the body. The immune system includes two levels of defence: the innate immune system, which is present at birth and is the body's first line of defense against disease; and the acquired immune system, which is activated in response to disease-causing agents entering the body. These two systems work synergistically; if the innate immune system fails to disarm an invading pathogen, the acquired system engages to destroy it. Immune system cells are specialized white blood cells, mainly lymphocytes, that target foreign cells, including infected or weakened cells, cells that have become cancerous, and abnormal cells resulting from gene mutations or exposure to toxins. The immune system regulates various immune cells to differentiate the body's normal healthy cells from foreign or damaged cells. Sometimes the immune system mistakenly attacks the body's own cells, which may lead to autoimmune diseases that destroy healthy tissue.
The innate immune system has three layers of defense or immune response:
Every organ system in the body is able to function better with protection against invasion by harmful micro-organisms and assaults from environmental toxins. The results of multiple studies of the immune system indicate that diet and exercise boost the effectiveness of a healthy immune system. Study subjects who exercised actively for 30 minutes or more neardaily for an extended period of time reported fewer incidents of acute illness, including upper respiratory infections, and reduced risk of developing chronic disease, than did control groups who remained sedentary. Study data remain consistent across crosssections of populations, including among young and old participants and a range of ethnic and genetic backgrounds. Near-daily moderate exercise such as brisk walking resulted in fewer illnesses overall. Study results also indicate that stress hormone levels, which are reported to influence immune system activity negatively and directly correlate to illness, are not as likely to become elevated in individuals who regularly engage in moderate exercise.
A direct relationship has also been established between nutrition and immunity. Early exhaustive research on malnutrition and immunity showed that malnourished children develop various infectious and chronic diseases. However, even when scientists look at seemingly healthy individuals in developed countries whose basic needs are met, and whose lifestyle permits exercise for purely health reasons (as opposed to exercise as a demand of labor), certain nutritional imbalances still appear to affect healthy immune response.
The nutrients found to be associated positively with immune function include: protein omega-3 fats, vitamin D, selenium, iron, zinc and vitamins A, E, folate, B6, and B12. Vitamin C also correlates positively with effective immune function, as well as adequate carbohydrate intake during times of vigorous exercise. Ample evidence exists that a diet too high in fats may depress immune system function even in individuals who actively exercise. The key to healthy immunity and prolonged quality of life is a proper balance of essential nutrients, the avoidance of foods too high in saturated fats, and the right amount of moderate and consistent exercise.
Industrialization, globalization, and urbanization have contributed to making processed, nutrient-poor foods more widely available, especially to low-income individuals and those without knowledge of nutrition. The same industrialization and automation that produce fast, easy, prepared foods, also promote easier, inactive lifestyles. The combination of poor diet and lack of exercise has created rising health issues shared by developed and developing countries. The diseases most often associated with poor nutrition and lack of exercise are cardiovascular diseases, obesity, diabetes, hypertension, and stroke, as well as certain cancers.
Foods available for mass distribution on the global market are often cheaply produced and shipped widely, requiring storage for long periods. Any food with a long shelf-life requires high preservative content and is typically high in saturated fat and sodium. Many such manufactured foods are low in unrefined carbohydrates, freshly harvested vegetables, fruits, and whole grains. However, the low price and wide availability of these nutrient-poor foods means they can be found in the cupboards of most homes and stocking the marketplace tables and shelves of most grocers. Many people around the world eat these foods, and because so many people are not exercising often enough or at all, preventable disease continues to increase globally.
To help ensure that the immune system defends the body against disease-causing organisms and toxins, an individual's overall health status must be maintained. Age, of course, reduces immune response, but age is not modifiable, and it is understood that risk of illness increases with aging. Boosting immunity at all stages of life is, therefore, an important preventative measure. Because immunity depends on a system, and not just one factor, enhancing immune system function requires a balanced lifestyle, especially in terms of modifiable factors such as diet, exercise, psychological stress, and the general pace of life. Choosing a healthy lifestyle is therefore the first line of defense.
A diet that includes essential nutrients is one of the most straightforward indicators of health status, as well as a predictor of disease and illness. Dietary changes are one of the most important modifiable lifestyle factors that can improve health. Regular exercise is the other critical modifiable lifestyle factor that influences overall health and disease prevention.
Regular exercise is shown to improve cardiovascular health, lower blood pressure, control body weight, and boost the immune system to protect against developing acute and chronic disease. Study results show that combining regular, near-daily exercise consisting of aerobic activity for 30 or more minutes along with a healthy, well-balanced diet is the best preventative measure against illness and chronic disease, current and future. A balanced approach to diet and exercise also reduces stress hormones, which reduces the rate of illness ever further.
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American Academy of Allergy Asthma and Immunology, 555 E. Wells Street, Suite 1100, Milwaulkee, WI, 53202-3823, (414) 272-6071, Fax: (317) 637-7817, http://www.aaaai.org .
American College of Sports Medicine, PO Box 1440, Indianapolis, IN, 46206-1440, (317) 637-9200, Fax: (317) 637-7817, (888) 463-6332, http://www.acsm.org .
American Dietetic Association, 120 S. Riverside Plaza, Suite 2000, Chicago, IL, 60606-6995, (800) 877-1600, firstname.lastname@example.org, http://eatright.org .
Julie Jordan Avritt
L. Lee Culvert