Health Benefits of Vitamin D - Fighting Infection

Infection

Vitamin D Crucial To Activating Immune Defenses

Scientists at the University of Copenhagen have discovered that Vitamin D is crucial to activating our immune defenses and that without sufficient intake of the vitamin, the killer cells of the immune system – T cells - will not be able to react to and fight off serious infections in the body.

For T cells to detect and kill foreign pathogens such as clumps of bacteria or viruses, the cells must first be 'triggered' into action and 'transform' from inactive and harmless immune cells into killer cells that are primed to seek out and destroy all traces of a foreign pathogen.

The researchers found that the T cells rely on vitamin D in order to activate and they would remain dormant, 'naïve' to the possibility of threat if vitamin D is lacking in the blood.

Chemical Reaction that Enables Activation

In order for the specialized immune cells (T cells) to protect the body from dangerous viruses or bacteria, the T cells must first be exposed to traces of the foreign pathogen. This occurs when they are presented by other immune cells in the body (known as macrophages) with suspicious 'cell fragments' or 'traces' of the pathogen. The T cells then bind to the fragment and divide and multiply into hundreds of identical cells that are all focused on the same pathogen type. The sequence of chemical changes that the T cells undergo enables them to both be 'sensitized to' and able to deliver a targeted immune response.

Professor Carsten Geisler from the Department of International Health, Immunology and Microbiology explains that "when a T cell is exposed to a foreign pathogen, it extends a signaling device or 'antenna' known as a vitamin D receptor, with which it searches for vitamin D. This means that the T cell must have vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won't even begin to mobilize. "

T cells that are successfully activated transform into one of two types of immune cell. They either become killer cells that will attack and destroy all cells carrying traces of a foreign pathogen or they become helper cells that assist the immune system in acquiring "memory". The helper cells send messages to the immune system, passing on knowledge about the pathogen so that the immune system can recognize and remember it at their next encounter. T cells form part of the adaptive immune system, which means that they function by teaching the immune system to recognize and adapt to constantly changing threats.

Activating and Deactivating the Immune System

For the research team, identifying the role of vitamin D in the activation of T cells has been a major breakthrough. "Scientists have known for a long time that vitamin D is important for calcium absorption and the vitamin has also been implicated in diseases such as cancer and multiple sclerosis, but what we didn't realize is how crucial vitamin D is for actually activating the immune system – which we know now. "

The discovery, the scientists believe, provides much needed information about the immune system and will help them regulate the immune response. This is important not only in fighting disease but also in dealing with anti-immune reactions of the body and the rejection of transplanted organs. Active T cells multiply at an explosive rate and can create an inflammatory environment with serious consequences for the body. After organ transplants, e.g. T cells can attack the donor organ as a "foreign invader". In autoimmune disease, hypersensitive T cells mistake fragments of the body's own cells for foreign pathogens, leading to the body launching an attack upon itself.

The research team was also able to track the biochemical sequence of the transformation of an inactive T cell to an active cell, and thus would be able to intervene at several points to modulate the immune response. Inactive or 'naïve' T cells crucially contain neither the vitamin D receptor nor a specific molecule (PLC-gamma1) that would enable the cell to deliver an antigen specific response.

The findings, continues Professor Geisler "could help us to combat infectious diseases and global epidemics. They will be of particular use when developing new vaccines, which work precisely on the basis of both training our immune systems to react and suppressing the body's natural defenses in situations where this is important – as is the case with organ transplants and autoimmune disease."

Most Vitamin D is produced as a natural byproduct of the skin's exposure to sunlight. It can also be found in fish liver oil, eggs and fatty fish such as salmon, herring and mackerel or taken as a dietary supplement. No definitive studies have been carried out for the optimal daily dosage of vitamin D but as a large proportion of the population have very low concentrations of vitamin D in the blood, a number of experts recommend between 25-50mg micrograms a day.

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The findings were published in Nature Immunology, (Vitamin D controls T cell antigen receptor signaling and activation of human T cells ) 10.1038/ni.1851, on 07 March, 2010.

Taking Vitamin D Reduces Risk of Respiratory Tract Infection

Treating infection-prone patients over a 12-month period with high doses of vitamin D reduces their risk of developing respiratory tract infection - and consequently their antibiotic requirement. This according to a new study by researchers at Karolinska Institutet and Karolinska University Hospital published in the online scientific journal BMJ Open.

"Our research can have important implications for patients with recurrent infections or a compromised immune defence, such as a lack of antibodies, and can also help to prevent the emerging resistance to antibiotics that come from overuse," says Peter Bergman, researcher at Karolinska Institutet's Department of Laboratory Medicine and doctor at Karolinska University Hospital's Immunodeficiency Unit. "On the other hand, there doesn't seem to be anything to support the idea that vitamin D would help otherwise healthy people with normal, temporary respiratory tract infections."

Vitamin D is synthesised in the skin through exposure to sunlight and obtained through certain foods. In Sweden there is a seasonal variation in vitamin D in the blood, the trough coming during the darker half of the year. Studies have shown that low levels of vitamin D can increase the risk of infection, and it has long been known that the vitamin can also activate the immune defence.

For the present study published in BMJ Open (December, 2012) the researchers examined whether treatment with vitamin D can prevent and relieve respiratory tract infections in particularly infection-prone patients. All the 140 participants from the Immunodeficiency Unit had symptoms of disease in their respiratory tracts for at least 42 days prior to the study. The patients were randomly divided into two groups, one of which received vitamin D in relatively high doses, the other a placebo. They were also asked to keep a diary recording their state of health every day during the year-long study period.

The results show that symptoms of respiratory tract infection declined by almost a quarter and the use of antibiotics by almost half. Vitamin D treatment was also tolerated well by all patients and gave no serious side-effects.

The effect of vitamin D on respiratory tract infection is controversial, and a major study from New Zeeland published recently in the scientific journal JAMA found that it did not reduce the incidence or severity of viral respiratory tract infections. However, the present study differs from the JAMA study in several important respects, which could explain their different results. The JAMA study examined a group of healthy people with initially normal levels of vitamin D in the blood, and used bolus dose administration (i.e. large doses on fewer occasions), which is thought to be less effective that daily doses.

"However, the most important difference is probably due to the fact that our participants had much lower initial levels of vitamin D than those in the New Zealand study," says Dr Anna-Carin Norlin, doctoral student and co-lead author of the study along with Dr Bergman. "There is evidence from previous studies that vitamin D supplements are only effective in patients who fall well below the recommended level, which also suggests that it would be wise to check the vitamin D levels of patients with recurrent infections."

Vitamin D's Potential to Reduce the Risk of Hospital-Acquired Infections

A paper recently published in Dermato-Endocrinology [Youssef et al., 2012] indicates that raising vitamin D concentrations among hospital patients has the potential to greatly reduce the risk of hospital-acquired infections. Hospital-acquired infections (HAIs) are a leading cause of death in the US health care arena, with an overall estimated annual incidence of 1.7 million cases and 100,000 deaths. HAIs in US hospitals generate an estimated $28.4 billion–$45 billion in excess health care costs annually. Patients are often vitamin D deficient since many diseases such as cancer, cardiovascular disease, and respiratory infections are linked to low vitamin D concentrations.

Pneumonia is the most likely HAI, followed by bacteremias, urinary tract infections, surgical site infections, sepsis, and others.

Vitamin D plays an important antimicrobial role. Among the antimicrobial actions are reducing local and systemic inflammatory responses as a result of modulating cytokine responses and reducing Toll-like receptor activation and stimulating the expression of potent antimicrobial peptides, such as cathelicidin and _-defensin 2. Cathelicidins are a family of peptides thought to provide an innate defensive barrier against a variety of potential microbial pathogens, such as gram-positive and gram-negative bacteria, fungi, and mycobacteria, at multiple entry sites, including skin and mucosal linings of the respiratory and gastrointestinal systems, as well as some viruses.

One of the advantages of vitamin D in combating HAIs is that it strengthens the innate immune response, thus overcoming the antibiotic resistance of many bacteria encountered in hospitals.

Optimal vitamin D concentrations are at least 30-40 ng/ml (75-100 nmol/l). The average white American has a concentration of 26 ng/ml, while the average African-American has only 16 ng/ml. Vitamin D concentrations have fallen in the past 20 years, in part due to spending less time out-of-doors. About half of those admitted to hospitals have concentrations below 20 ng/ml, thus making them more susceptible to HAIs. Raising vitamin D concentrations would reduce the rate of diseases such as many types of cancer, cardiovascular disease, hip fractures, and respiratory infections, thereby reducing the rate of hospital admissions as well as HAIs once admitted.

In an accompanying editorial, David McCarthy, M.D. outlined what hospitals could do to overcome vitamin D deficiency among hospital patients. Among these recommendations is making high-dose vitamin D3 (5,000 and 50,000 IU) capsules available to the patients.