**note that this is a work in progess :) **
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function properly. Detection is complicated as pathogens can evolve rapidly, and adapt to avoid the immune system and allow the pathogens to successfully infect their hosts.
from Wikipedia http://en.wikipedia.org/wiki/Immune_system
The immune system is a complex system that involves many processes, it is closely linked with endocrinological responses which helps explain adrenal exhaustion, liver toxicity, blood sugar issues, thyroid involvement, gonadal and hypothalamus/pituitary.
Vitamin A (Beta-carotene and other carotenoids)
The following is from Whole Foods http://www.whfoods.com/genpage.php?tname=faq&dbid=24
Protein and your immune system
Much research has shown that protein malnutrition can have a variety of untoward effects on the immune system. In fact, protein malnutrition may be an important contributing factor in HIV seroconversion (the process by which a person with primary exposure to Human Immunodeficiency Virus becomes infected with that virus). Research studies have show that deficiency of high-quality protein protein can result in depletion of immune cells, inability of the body to make antibodies, and other immune-related problems. In addition, animal studies have shown that the immune system can be significantly compromised with even a 25% reduction in adequate protein intake.
Protein is composed of the 20 amino acids your body needs for growth and repair, and some of these amino acids appear to be particularly important for immune functioning. For example, the amino acids called glutamine and arginine are being considered as nutrition therapy in pre-surgery patients because of their ability to stimulate the immune system. Interestingly, it is not just deficiency of these amino acids that can compromise the immune system, an imbalance in the ratios among amino acids can also affect the immune response.
Therefore, a diet that supports a healthy immune system should contain foods providing high-quality, complete protein, such as that found in eggs, fish, shellfish, and venison. Many vegetables and grains are also excellent sources of many of the immune-stimulating amino acids and, together with other protein sources, are particularly beneficial. The recipes on this web page provide many excellent menus for a meal with complete protein, such as the Baked Seafood with Asparagus, or Poached Fish with Chinese Cabbage.
The essential vitamins for healthy immune function
As discussed above, your body uses a variety of responses to maintain its defense against harmful pathogenic organisms in the environment; therefore, it may not be surprising that nearly all of the vitamins are necessary to maintain and promote some aspect of your immune function. Some vitamins have received more attention in the research literature since they are particularly important to a healthy immune system.
Much has been written about the role of vitamin C in supporting the immune system, in part because it has been promoted as an immune stimulant by the noted scientist and Nobel Prize Laureate, Linus Pauling. Vitamin C appears to support a decrease in the length of time and severity of symptoms associated with upper respiratory viral infections, promote phagocytic cell functions, and support healthy T-cell function. Vitamin C also provides antioxidant activity to support healing at sites of inflammation. An excellent source of vitamin C is citrus fruit. Many vegetables are also excellent sources of vitamin C, such as fresh parsley, raw cauliflower, mustard greens and Romaine lettuce.
Many of the B-vitamins are also very important in supporting a healthy immune system. For example, vitamin B5 (pantothenic acid) promotes the production and release of antibodies from B-cells, and deficiency of vitamin B5 results in reduced levels of circulating antibodies. Folic acid deficiency leads to a decrease in T-cells and can result in reduced effectiveness of the soluble factors as well. Vitamin B6 deficiency consistently impairs T-cell functioning and results in a decrease in blood lymphocyte counts. Deficiencies in vitamins B1(thiamin) and B2 (riboflavin) may impair normal antibody response, and low vitamin B12 appears to inhibit phagocytic cells and possibly T-cell function.
Almost all whole grains, vegetables and fruits can serve as excellent sources of at least some of these vitamins, but some vegetables are particularly beneficial since they are excellent sources of many of these immune-supporting vitamins. In particular, Romaine lettuce is an excellent source of vitamins B1, B2, C, and folate. Cooked turnip greens and boiled spinach are excellent sources of folate, vitamin B6 and vitamin C. And cooked cauliflower is an excellent source of vitamin C and folate and a very good source of vitamin B5 and B6. Raw crimini mushrooms are also an excellent source of vitamin B2 and vitamin B5. Red bell peppers are an excellent source of vitamin B6. Vitamin B12 can be obtained from protein-providing foods such as fish, shellfish, venison and calf's liver.
The fat-soluble vitamins, vitamin A, vitamin E and vitamin K are also important to overall health. Vitamin A deficiency has been shown to impair antibody function and T-cell activity. Vitamin E is an important antioxidant and supports a healthy inflammatory response. Vitamin E is also an important component of all cell membranes and promotes healthy cellular functioning overall. T-cells and B-cells from vitamin E-deficient animals show depressed responses, and tumors have been shown to grow faster in vitamin-E deficient animals. Vitamin K supports a healthy blood-clotting ability in your body, and this is necessary for seclusion of areas of infections and injury in the healing process. Cooked turnip greens and boiled mustard greens, mentioned above, are also excellent sources of vitamins E and A, as well as boiled Swiss chard. Other excellent sources of vitamin A include many vegetables such as spinach, fresh parsley and carrots. Concentrated sources of vitamin K include raw cauliflower, as well as most green vegetables such as spinach and asparagus.
Minerals that support your immune system
Zinc is one of the minerals in food that has received the most attention for its ability to support immune function. Zinc is a potent immunostimulant, and its deficiency can result in profound suppression of T-cell function. Children with severe zinc deficiencies show signs of growth retardation and susceptibility to infections. However, an excess of zinc has also shown negative effects on immune function and can inhibit the phagocytic cells (macrophages and neutrophils). So, maintaining adequate but not excessive levels of zinc is important. This is one reason food is such an excellent source of obtaining nutrition versus supplementation; food contains a balanced variety of the micronutrients whereas supplementation with individual nutrients can lead to too much of some and not enough of others. Healthy levels of zinc can be provided by including the good sources of zinc, such as boiled Swiss chard, collard greens, and both summer squash and winter squash, or the very good or excellent sources of zinc like lamb, raw crimini mushrooms and calf's liver in your diet.
Many other minerals are important in supporting immune function. Clinical research studies have shown that iron deficiency results in impaired response to antibodies, and defective phagocytic cell functioning. Copper deficiency is associated with an increase in infections and may impair development of immune cells such as T-cells and the phagocytic cells. Selenium and manganese are important for supporting healing from inflammation and may be immunostimulants. Selenium can be obtained from fish and shellfish, as well as tofu and whole grains. Excellent sources of copper are turnip greens, calf's liver and raw crimini mushrooms, and very good sources include spinach, asparagus and summer squash and boiled Swiss chard. Iron can be provided by fresh parsley, spices such as thyme or cinnamon, tofu, beans and peas, and many other vegetables such as spinach and Romaine lettuce.
Antioxidants and phytonutrients that promote healthy immune function
Reactive oxygen species, free radicals and other damaging molecules are generated at sites of infection and inflammation. Your body needs these molecules at the site of infection to help kill unhealthy cells; however, when your antioxidant systems are not functioning, or when not enough antioxidants are present in your diet, these molecules are not disarmed after they have done their jobs and can become damaging to healthy tissue as well. Many fruits and vegetables provide antioxidants and phytonutrients that help maintain healthy tissue around the sites of infection and support healing. Fruits and vegetables, especially colored foods like strawberries, cherries, carrots, and tomatoes contain many beneficial phytonutrients with antioxidant potential. More detailed information on the health benefits of phytonutrients can be obtained from the FAQ: "What is the Special Nutritional Power Found in Fruits and Vegetables".
Are there foods that are bad for my immune system?
Your immune system is not just involved in fighting invaders like bacteria, but also becomes activated when you eat foods to which you are intolerant or allergic. Reactions to allergic foods can be quick, like the anaphylactic reaction often seen with peanut or shellfish allergies, but food allergy reactions can also be delayed and cause a number of symptoms like headaches, fatigue, muscle aches, rashes and other systemic (whole body) effects. The most common allergenic foods include peanuts and shellfish, cow's milk, wheat, and soy; however, everyone is unique in their food intolerances and allergies.
Processed foods and foods produced with pesticides or not grown organically may also be problematic for your immune function. Toxic metals such as cadmium, lead and mercury are immunosuppressive. Some pesticides and preservatives can negatively effect the gastrointestinal lining. Food additives can also have untoward effects on the nutrient content of the food. For example, sulfites destroy thiamin-vitamin B1 in foods to which they have been added.
How do I keep a healthy "balance" in my immune system?
Your immune system is developed to be able to kill cells, such as bacteria cells or viruses; your immune cells can act against cancer cells within your body as well if it is able to tell that these cells are unhealthy to you. However, without proper control and the ability to differentiate healthy from unhealthy cells, your immune system can mistakenly kill your own healthy cells. Your inflammatory response is also developed to support healing, but when this response becomes overly active, it can become destructive. Autoimmune system diseases like rheumatoid arthritis and multiple sclerosis, susceptibility to infections, and wounds that won't heal are some of the repercussions of immune system imbalance and dysfunction. Therefore, healthy immune and inflammatory responses must maintain a delicate balance to achieve protection without causing self-destruction.
Your body has a complex means of recognition on your cells' membranes to help your immune system. Some specific soluble factors of your immune system are also involved in turning-off your immune response. How well these responses function is defined in part by your genes; however, recent research has suggested that diet plays a much larger role in autoimmune system dysfunction than was once thought. For example, research has shown an association with low levels of vitamin D and increased risk of some autoimmune diseases, such as multiple sclerosis. Concentrated sources of vitamin D include cow's milk eggs and shellfish such as shrimp and fish such as cod.
The omega-3 fatty acids, which are produced in your body from the essential omega-3 fat - alpha-linolenic acid - have been studied for their effects on the immune system and inflammatory response. Diets low in omega-3 fatty acids are associated with chronic inflammatory conditions and autoimmune diseases. In order to achieve a more beneficial ratio of omega-3 fatty acids in your body, it is important to decrease the amount of omega-6 fatty acids in your diet, while increasing the amount of omega-3 fatty acids. This can be accomplished by reducing your consumption of meats, dairy products, and refined foods, while increasing consumption of the omega-3 rich foods such as wild-caught cold-water fish like salmon, flaxseed oil, walnuts, and leafy green vegetables.