Monday, May 3, 2010

Rheumatoid arthritis, sunlight deprivation and vitamin D—so what’s new?

An interesting study on rheumatoid arthritis (RA) and latitude appeared recently in the online journal, Environmental Health Perspectives.[1] The researchers found that the disease was considerably more prevalent among those living at higher latitudes than at lower latitudes. They had expected to find a relationship between air pollution and RA, but such a relationship did not exist. They concluded that the correlation of high latitudes to RA was probably due to less vitamin-D producing sunlight exposure and consequent vitamin D deficiency. My response is, “This is news?”

There should have been so expression of surprise about the results. RA is one of many autoimmune diseases, and it has long been known that vitamin D has a profound, positive influence on those diseases.[2] These are diseases in which the immune system attacks the body’s own healthy tissue, mistaking that tissue for a foreign invader. When this happens, a specialized immune-system cell (called a T cell) assaults and kills some of the tissue of a targeted organ. Autoimmune diseases, then, are caused by T cells gone awry. In the case of rheumatoid arthritis the immune system attacks the collagen-producing cells of the joints. T cells in a person with an autoimmune disease lack the “intelligence” to recognize that they are attacking the wrong tissue. That intelligence, in part, comes from vitamin D, the receptors of which are found in large quantities in mature T cells and even larger concentrations in immature T cells produced in the thymus gland. Without vitamin D stimulation of the receptor sites, these cells will not function properly. When vitamin D is present however, they have the ability to discern between foreign invaders and the body’s own tissue. Animal experiments show that vitamin D acts as a “selective immunosuppressant” (see footnote 2), meaning that it gives T cells the ability to distinguish between “good and evil.” It is this ability to reduce the autoimmune response, as well as its anti-inflammatory properties that are likely responsible for the lessened risk of RA in sun-deprived areas, and this is further corroborated by the fact that RA is also more severe in winter,[3] a time of less sunshine, and a time when sunlight exposure in northern latitudes does not produce vitamin D.

In another report from researchers in Ireland (a northern country with little sunlight exposure), it was shown that 70% of patients had low vitamin D levels and that 26% were severely deficient.[4] However, in that report, 21 ng/ml was considered as the deficiency level and 10 ng/ml as the severe deficiency level. In reality, a level of 21 is dangerously deficient. It is likely that all of these patients had levels under 32 ng/ml, now considered the lowest level for good health. My opinion is that levels of 50 to 60 are optimal.

Considering this information, it should have come as no surprise that RA was more common at higher latitudes. It is time to return to the sun in the summer and to find ways of maintaining optimal vitamin D levels in the winter through the use of sun lamps.


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