A well-functioning immune system is essential for good health, as it plays a vital role in protecting the body from the vast numbers of disease-causing organisms and other substances with which it comes into contact. The job of the immune system is to distinguish between normal body cells and foreign or abnormal cells. As with all body systems, immune balance is the key. Over-activity leads to allergies and autoimmune diseases, and under-activity increases the risk of infections. The immune system is also vital for recognizing and destroying cancer cells.

The immune system is composed of specialized tissues, organs, cells and chemicals that recognize and destroy foreign invaders. The skin and mucous membranes form a barrier against unwanted organisms and substances. Immune cells include white blood cells such as T lymphocytes, which have many functions including control of other immune cells; and B lymphocytes, which produce antibodies. There are also natural killer cells and scavenger cells known as monocytes and macrophages, which engulf foreign particles. The cells of the immune system also produce substances such as interferon, which has antiviral effects.

The best way to keep the immune system working well is to stay in good general health. It is important not to allow infections to persist as this puts a strain on the immune system. Diet, medications, pollution, toxic chemicals, stress levels and emotional state all affect the workings of the immune system. Overuse of antibiotics is common nowadays and may prevent the immune system from becoming strong enough to deal with infectious agents. Other medications that can adversely affect the immune system include steroids. These drugs are often given for long periods in the treatment of disorders such as arthritis and asthma. Improving lymphatic circulation can help to boost the immune system. Exercise, massage and herbal remedies are helpful for this.



An autoimmune disease is one in which the immune system mistakenly attacks the body's own tissues. Some of the most common autoimmune diseases include arthritis, systemic lupus erythematosus (SLE), and possibly inflammatory bowel disease. There may be a genetic component to autoimmune diseases and they may also be caused by infections and injuries. Stress and emotional factors also seem to contribute. Supporting the immune system through diet and lifestyle is vitally important in the treatment of autoimmune diseases.



An allergy is an inappropriate response by the immune system to a substance that is usually harmless. There are many causes of allergy, the most common being airborne particles such as mold, dust and pollen, certain foods, chemicals and drugs. Allergic responses play a role in many disorders, including asthma and hayfever. Supporting the immune system can be valuable in the treatment of allergic disorders.


Diet and Immune Function

The strength of the immune system is an important factor in the response to infection. Nutrition plays a vital role in the functioning of the immune system and a poor diet increases the susceptibility to infection and exacerbates autoimmune diseases. Even single nutrient deficiencies can compromise the immune system. Infections also increase the demand for nutrients to help fight infection and repair the damage to tissues.

As well as being good for general health, a low protein, high carbohydrate diet with plenty of fruits, vegetables, and fiber is beneficial for the immune system. An immune-boosting diet is also low in polyunsaturated vegetable oils and products made from them. These fats readily form free radicals that damage immune cells. High protein diets are damaging to the immune system as residues of protein metabolism can cause irritation, especially in people prone to allergy and autoimmunity. Milk protein is a common irritant of the immune system. Foods of animal origin, which tend to be high in protein, often contain residues of antibiotics and steroid hormones that can weaken immunity.

The effectiveness of the immune system declines with age and older people are often more susceptible to infection than younger people. In addition, the elderly are at greater risk of low intake of several vitamins and minerals known to influence the immune response. Recent studies have shown that supplementing the elderly with single nutrients or mixtures of vitamins and minerals at levels that exceed the RDAs significantly improves certain components of the immune response.


Vitamins, Minerals and Immunity

Vitamin and mineral supplementation can play an important role in the maintenance of normal immune function in the elderly. In a placebo-controlled 1994 study, researchers compared the effects of a vitamin and mineral supplement or placebo on immune responses of 56 people, aged from 59 to 85. Immune function was assessed by the use of the delayed hypersensitivity skin response test after six months and one year. The results showed that immune function was enhanced in the group receiving the supplements but not in the group receiving the placebo.1 In another study, improved immune response was associated with decreased frequency of infectious diseases, indicating that nutrient-induced immunological improvement clinically enhances the health of elderly people.2


Antioxidants are vital for maintaining optimal immune function as they act to prevent free radical damage to immune cells and to the thymus gland. This gland plays an important role in ensuring optimal immune function, via effects on white blood cells and other parts of the immune system.

Antioxidant vitamin concentrations are often lower in those with infections than in those who are healthy. Optimal amounts of antioxidants are necessary for maintenance of the immune response. This is particularly important in older people as age-associated decline of the immune response, particularly of T cell-mediated function, is well documented. The well-known age-related increase in free radical formation and lipid peroxidation contributes to this decline.

Recent clinical trials have found that antioxidant supplementation can significantly improve certain immune responses, including increasing the activation of cells involved in tumor immunity in the elderly. Supplementation with the antioxidant vitamins also protects immune responses in individuals exposed to certain environmental sources of free radicals.3

In a 1991 study, 30 elderly hospital patients were randomly allocated to receive either placebo or dietary supplementation with vitamins A, C and E for 28 days. Nutritional status and cell-mediated immune function were assessed before and after the period of supplementation. The results showed that, in those who had taken the supplements, cell-mediated immune function improved, whereas no significant changes were noted in the immune function of the placebo group.4

Vitamin A

Vitamin A is vital for the development of the body's barriers to infection and stimulates and enhances many immune functions, including antibody response and the activity of various white blood cells such as T helper cells and phagocytes. This immune-enhancing function promotes healing of infected tissues and increases resistance to infection. Episodes of acute infection may deplete body stores of vitamin A, possibly by increasing excretion, suggesting that vitamin A requirements may be higher during infection.

Death rates and susceptibility to infection and diarrhea are higher in children with vitamin A deficiency, particularly in developing countries. However, vitamin A deficiency may also contribute to susceptibility to infection in developed countries. A 1992 study involving 20 children with measles in Long Beach, California found that half of them were vitamin A-deficient.5 Measles may increase the body's utilization of vitamin A, possibly because of the rapid destruction of epithelial surfaces.

Vitamin A deficiency is common in HIV-positive people and this may be due to metabolic changes associated with HIV infection. Vitamin A deficiency is often seen in HIV-positive pregnant women and severe deficiency increases infant mortality and the risk of mother-to-child transmission of HIV.

Vitamin A supplements have been used to enhance resistance to infection and to treat measles and respiratory infections, particularly in areas where vitamin A deficiency is widespread. A recent research review analyzing the results of several studies found that adequate vitamin A intake in children resulted in a 30 per cent decrease in deaths from all causes. Children in developing countries are often at high risk of vitamin A deficiency. In developed countries, ensuring adequate vitamin A intake is particularly important in those with life-threatening infections such as measles, and in those at risk of relative deficiency, such as premature infants.6

Beta Carotene

Beta carotene has been shown to stimulate and enhance many immune system processes. It increases the numbers of immune cells such as B and T lymphocytes, and may enhance natural killer cell activity. T cells play a very important role in determining immune status and are produced by the thymus gland, which is particularly sensitive to free radical damage. Beta carotene protects macrophages, white blood cells which engulf and destroy foreign substances. It also facilitates communication between immune cells and makes the stimulatory action of interferon on the immune system more powerful.

In a 1997 double-blind, placebo-controlled study done in the UK, researchers tested the effects of daily doses of 15 mg of beta carotene in 25 healthy, adult male nonsmokers. Their findings showed improvement in function in various parts of the immune system, including white blood cells known as monocytes, which are involved in surveillance of tumors.7

Vitamin C

Vitamin C is critical to immune function as it is involved in antibody production and white blood cell function and activity. Other functions include the production of interferon, an antiviral and anticancer substance. Vitamin C requirements are raised when the immune system is under stress. In a study published in 1997, French researchers assessed vitamin C levels in 18 elderly patients in hospital. The patients were divided into three groups: those with acute infection, those who were malnourished, and a control group. Those with acute infection had considerably lower vitamin C levels than those in the other groups.8

A 1994 study tested vitamin C or placebo supplementation on 57 elderly patients admitted to hospital with acute respiratory infections (bronchitis and bronchopneumonia). The researchers found that patients supplemented with vitamin C showed significantly more improvement than those on placebo. This was particularly the case for those starting the trial most severely ill, many of whom had very low plasma and white cell vitamin C concentrations.9

Vitamin C has also been shown to help the immune system recover from exposure to toxic chemicals. In a 1997 study, researchers studied the effect of vitamin C on the function of several immune cells (natural killer, T and B cells) in patients who had been exposed to toxic chemicals. Fifty-five patients were given buffered vitamin C in water at a dosage of 60 mg per kg body weight (around 4g for the average man). Twenty-four hours later, the researchers tested immune cell function. The results showed that natural killer cell activity was enhanced up to ten-fold in 78 per cent of patients. B and T cell function was restored to normal.10

Vitamin C may reduce the duration of the common cold and also the severity of symptoms such as sneezing, coughing and sniffling. Its use as a cold treatment is controversial but it seems to have several effects, including reducing blood levels of histamine which can trigger tissue inflammation and a runny nose. It may also protect the immune cells and surrounding tissue from damaging oxidative reactions that occur when cells fight bacteria.11

Vitamin E

Vitamin E is essential for the maintenance of a healthy immune system as it protects the thymus gland and circulating white blood cells from damage. Vitamin E is particularly important in protecting the immune system from damage during times of oxidative stress and chronic viral illness.

Several studies have suggested that vitamin E supplements can help to boost immune function. A study reported in the Journal of the American Medical Association in 1997 provides more support for this. The study involved 88 healthy people, aged 65 or older. Those who took 200 mg (300 IU) each day for about four months showed an improvement in immune response. Researchers assessed the effects of either 60 mg (90 IU), 200 mg (300 IU) or 800 mg (1333) on a measure of immune system strength known as delayed hypersensitivity skin response. The results showed that those who took 200 mg a day had a 65 per cent increase in immune function. Those taking 60 mg or 800 mg of vitamin E also showed some improvements in immune function, but the ideal response was seen in those taking 200 mg. In other tests, those who took the supplements produced six times more antibodies to hepatitis B after being given the vaccine than those who took placebo. They also produced more antibodies against tetanus infection.12


Selenium is important in maintaining resistance to disease. As part of the antioxidant enzyme, glutathione peroxidase, it may enhance immune function by protecting white blood cells from free radical damage. It also appears to increase antibody production, and accelerate the production of white blood cells and enhance their effectiveness in attacking and destroying harmful micro-organisms.

B Vitamins

B vitamins are also essential for the functioning of a healthy immune system. Vitamin B6 plays a vital role in maintaining a healthy immune system by affecting functions such as cell multiplication and antibody production. Many different aspects of the immune system are affected by vitamin B6 deficiency including the quality and quantity of antibodies and the number of white blood cells.13 Vitamin B6 supplementation may boost the immune system in older people, thus reducing the risk of infection and possibly cancer.

Vitamin B12 deficiency leads to reduced numbers of white blood cells which causes increased susceptibility to infection. Recent research has shown that elderly patients with low vitamin B12 levels have impaired antibody response to bacterial vaccine, even in those with no clinical signs of deficiency.14

Biotin deficiency also affects the functioning of the immune system. A recent animal study showed a decrease in white blood cell function with biotin deficiency.15 Pantothenic acid is necessary for the synthesis of antibodies. It is also involved in wound-healing. Supplements have been used to boost immunity during viral infections16 and to speed up wound-healing.

Vitamin D

Vitamin D is involved in the regulation of the immune system. It has several functions, including effects on white blood cells known as monocytes and lymphocytes, and seems to suppress some immune functions. Because of its effects on the immune system, many researchers are investigating the possibility of using vitamin D and related compounds to treat autoimmune disorders and to suppress rejection of transplanted organs.


Copper is important in developing resistance to infection. Copper deficiency can lead to reduced resistance to infection as white blood cell activity and cellular immune responses are reduced. The ratio of zinc to copper may also affect immune system effectiveness. Susceptibility to disease seems to increase when copper intake is high and zinc intake is low.


Iron is involved in the maintenance of a healthy immune system and the immune response can be impaired in iron-deficient people. Chronic yeast infections and herpes infections may be more common in people who are iron-deficient. Certain types of immune cells rely on iron to generate the oxidative reactions that allow these cells to kill off bacteria and other pathogens. When iron levels are low, these cells cannot function properly.

However, iron is an important nutrient for bacteria and in conditions where iron levels in the tissues are too high, such as the iron overload disorder hemochromatosis, defense against bacterial infections may be impaired. Excess iron can also generate free radicals which can damage the immune system.


Zinc is considered one of the most important nutrients for the immune system as it is necessary for healthy antibody, white blood cell, thymus gland and hormone function. It is therefore vital in maintaining resistance to infection and in wound-healing.

Immune function is affected by zinc deficiency, which results in a decrease in the numbers of several types of T cells, natural killer cells and other components of the immune response. This leads to increased susceptibility to infection and wound-healing time.

Zinc supplementation improves immune function in those who are deficient. It increases the activity of the thymus gland, improves antibody responses and enhances the functioning of white blood cells. It has been shown to inhibit the growth of bacteria and possibly viruses. Zinc supplements have also been shown to boost levels of interferon, a protein which is formed when cells are exposed to viruses and which helps to fight infection. 17

Researchers at the University of Medicine and Dentistry of New Jersey, Newark tested the effects of one year of supplementation with zinc and other micronutrients on cellular immunity in elderly people. The patients, aged 60-89, were either given a placebo, 15 mg of zinc, or 100 mg of zinc daily for 12 months. The results showed improvements in some aspects of immunity.18 In another double-blind, randomized, controlled trial, published in 1998, researchers tested the effects of vitamin A and zinc (25 mg as zinc sulfate) supplements in 136 residents of a public home for older people in Rome. The results showed that zinc supplementation improved cell-mediated immune response.19

Many studies show beneficial effects of zinc in the treatment of diarrhea, a major cause of death in children in developing countries. Researchers involved in a double-blind trial carried out in India involving almost 600 children aged 6-35 months found that zinc supplements reduced diarrhea outbreaks.20 However, long-term use of zinc in doses above 150 mg have been reported to cause the suppression of immune function.

Other Nutrients

Coenzyme Q10

Coenzyme Q10 supplements have also been shown to improve immune function.21

Essential Fatty Acids

Essential fatty acid deficiency may adversely affect immune function and supplements may be useful in promoting optimum function. Studies on the immune T cells in cancer patients taking fish oil capsules suggest that omega-3 fatty acids bring about beneficial changes. Essential fatty acids are also used to treat autoimmune disorders.

Herbal Medicine and Immunity

There are several herbs which have powerful immune-enhancing effects. These include echinacea (Echinacea angustifolia and E. purpurea), astragalus (Astragalus membranaceous), goldenseal (Hydrastis canadensis), licorice (Glycyrrhiza glabra), ginseng (Panax ginseng and Eleutherococcus senticosus), garlic (Allium sativum) and cat's claw (Pau d'Arco). Mushrooms such as shiitake, reishi and maitake also help to enhance immune system function.



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