01 July 2010
The immune system is responsible for the body’s own defenses. It has the task of fighting harmful substances like microorganisms and viruses that have invaded the body. It consists in part of white blood cells (leukocytes) that develop from the stem cells of the bone marrow. These include B lymphocytes, T lymphocytes, natural killer cells, granulocytes and monocytes. Lymph and blood vessels enable the cells of the immune system to circulate and detect antigens. The stronger the immune system, the better the body can defend itself against pathogens, deactivate damaged cells and disease.
The immune system is positively influenced by a whole series of factors. These include adequate physical exercise, weight loss when overweight, giving up smoking and a smart diet. Vitamins are essential for a well-functioning immune system. New research emphasizes that interactions between different vitamins is of particular importance. Only together, working as a team, can vitamin A (and its precursor, beta-carotene), the B vitamins, and vitamins E, D and C really get to grips with maintaining immunity.
Vitamin A
Apart from iron and iodine deficiency, vitamin A deficiency is the most common deficiency worldwide. Although pronounced vitamin A deficiency is found primarily in developing countries, several studies have shown that the supply of vitamin A may also be inadequate in developed countries, albeit without visible clinical signs. Even before the incidence of visible consequences such as night blindness and general blindness, increased susceptibility to respiratory infections may be observed.
The increased susceptibility to infection is explained by the importance of vitamin A in maintaining intact mucous membranes in the respiratory tract. The mucous membranes of the mouth and throat represent the first physical barrier that carriers of infection need to overcome. An inadequate supply of vitamin A leads to immobility of the cilia (tiny hairs) of the mucous membranes of the nose and lungs, which cannot then function. Only mobile cilia are able to eject invading germs or other harmful substances from the airways before they make us ill. As the cilia become less mobile, more thick mucus forms, in turn becoming a breeding ground for germs. The intestinal mucosa also have an important barrier function: Here, too, vitamin A has a crucial role to play in protecting the organism against pathogens.
It is thought that vitamin A also has a direct effect on the immune system, where it influences the production and differentiation of white blood cells. This applies above all to the lymphocytes that produce antibodies, which have protective activity in the digestive tract. As a vitamin A precursor, beta-carotene plays an important role in preventing the development of autoimmune diseases.
In this context the interaction with vitamin D is important, because vitamins A and D act in close cooperation to form a strong team. Even if the supply of vitamin A is adequate, problems arise when intake of vitamin D is insufficient. If one of these two vitamins is not present in sufficient quantities, the other cannot exert its optimal effect.
B vitamins
Vitamins of the B complex appear to be involved in immune defense in various ways. Together vitamins B6, B12 and B9 (folate) are involved in the production of proteins and DNA relevant to the immune system. B vitamins are particularly associated with an improvement in immune reaction in the severely ill.
Inadequate consumption of these vitamins can have negative effects on the immune system. Thus a poor supply of vitamin B1 is associated with an increased risk of parasitic infections. In vitro, vitamin B6 deficits have been observed to negatively impact the cellular immunity of healthy older people. It was possible to counteract this negative impact with an adequate supply of vitamin B6.
Vitamin C
A positive influence of vitamin C on the immune system has often been reported. The incidence of pneumonia, malaria and diarrhea has been reduced in children in developing countries by administering vitamin C and zinc. In industrialized countries, consumption of vitamin C rich foods is regarded as a way of preventing colds and diseases of the upper respiratory tract – especially in sportspeople, children and older people.
Vitamin C appears to be able to fight pathogens at a very early stage of invasion. It accumulates in the white blood cells and can improve their antibacterial activity. Studies have shown that vitamin C levels fall considerably during an infection. There are indications that the frequency and duration of respiratory infections and colds may in some instances be reduced by an adequate intake of vitamin C.
Vitamin D
In addition to its central role in regulating calcium and phosphate metabolism, vitamin D also plays a crucial role in immune defense. In most cases, it acts in conjunction with vitamin A.
Before the discovery of antibiotics, tuberculosis patients were treated with cod liver oil and UV radiation. Medical scientists only discovered why this therapy was successful many years later. Today we know that the two measures improve the supply of vitamin D and that vitamin D in turn causes the body to produce the antimicrobial substance cathelicidin, which is active against tuberculosis bacteria. Studies have revealed that tuberculosis patients have lowered levels of vitamin D.
There is much to indicate that when vitamin D levels are low, the killer cells of the immune system, the T cells, cannot become active and thus cannot fight the pathogens in the body. Only after the inactive immune cells have been converted into active killer cells are they able to render attackers harmless. For this conversion they appear to need vitamin D so that if the vitamin is lacking the T cells remain inactive.
An inadequate supply of vitamin D would therefore seem to be associated with an increased risk of infections of the upper respiratory tract. Research indicates that a good supply of vitamin D can reduce the risk of infection. A recent Japanese study with schoolchildren showed that increased consumption of vitamin D during the winter months (December to March) protected study participants against seasonal influenza.
Vitamin E
The term vitamin E covers a group of eight fat-soluble vitamins, of which alpha-tocopherol is the most important for human beings on account of its efficacy. Vitamin E is one of the antioxidants that can render free radicals harmless. The most important activity of the vitamin takes place in the cell membranes. There it protects the cell walls against harmful, extremely reactive molecules that are also produced in the course of the body’s own immune activity.
In recent years, there have been growing signs that vitamin E also has direct effects on immune activity, especially in relation to diseases like sepsis and in older people. Severe sepsis, known familiarly as blood poisoning, is a complex systemic inflammatory reaction that is still today fatal in 60% of cases. It has been established that alpha-tocopherol levels in serum in patients with severe sepsis were reduced to 68% of the values in healthy subjects. The lower the alpha-tocopherol levels, the more severe the disease. When alpha-tocopherol concentrations are low, programmed cell death, a kind of “suicide program” (apoptosis) by lymphocytes, increases. This increased cell death of lymphocytes during sepsis is generally viewed as harmful because it weakens the immune system. Animal experiments have indicated that vitamin E deficiency causes a gene regulation that makes cells more disposed to apoptosis, or programmed cell death.
The immune system becomes weaker as we age. One way in which this expresses itself is that the activity of T cells which are important for immune activity becomes weaker. Several studies have demonstrated that in some circumstances vitamin E can improve T cell activity in old age. In addition, some studies indicate that infections of the upper airways and colds are less frequent when vitamin E intake is sufficient. However, vitamin E also demonstrates its strengths best as part of a team. It can only evolve its activity in interaction with vitamin C.
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