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      Dr. Mercola's Comment: 
      This article is important only if you are interested in preventing cancer or autoimmune disease. First let's review the connection of vitamin D to cancer.


      As it says in the article, it has been known for more than 60 years that there is an inverse correlation between sun exposure and cancer deaths. It was also recognized that there was both a direct association between skin cancers and sun exposure and an inverse association between skin cancers and internal cancers. In fact, noting these two associations, researchers initially suggested that development of skin cancer brought immunity against various internal cancers. However, the negative correlation between sun exposure and several common cancers is very strong and has been documented repeatedly in the scientific literature. It is now understood to be a function not of immunity per se, but of vitamin D concentrations, and, of course, does not require development of skin cancers at all.


      It has long been known that vitamin D protects against bone loss, but it clearly has other functions. Calcitriol is the activated form of vitamin D that has two hydroxyl groups to it that are added by your liver and your kidney. Calcitriol has been shown to induce cell differentiation and to control cell proliferation--in simpler terms it protects against cancer. People with a low vitamin D level, whether because they have little sun exposure or because they have extensive pigmentation that limits sun-caused vitamin D synthesis in the skin, are less able to make calcitriol (activated vitamin D) in an amount sufficient to exert the controls over cell proliferation that are needed to reduce cancer. 


      Only relatively recently has a reliable measurement of serum 25 hydoxy vitamin D been available, and most of the physiology of vitamin D had been worked out before that time and thus was unconnected to specific levels of vitamin D supplementation. So current measurements of vitamin D are usually related to laboratory "reference" ranges and these ranges record what is observed in people who are considered "normal" only because they do not have recognizable rickets or osteomalacia. Absolutely NO reference is made to vitamin D's ability to control cancer or autoimmune disease.


      So if you have any interest in preventing cancer and autoimmune diseases like MS and rheumatoid arthritis then get your vitamin D level checked. But be armed with the correct information. Nearly all physicians are not aware how to have this checked and how to interpret the normal reference ranges. So print out the article on vitamin D testing for your records and also for your doctor so he or she can become aware of this vitally important nutrient.


      This is especially important this time of year as most of our vitamin D levels are decreasing due to limited sun exposure. This is definitely the time of year to switch from fish oil to cod liver oil, which is an excellent source of vitamin D, if you live in the United States. 

      Related Articles:

        Breakthrough Updates You Need to Know on Vitamin D

        Vitamin D May Prevent Skin Cancer

        Vitamin D for Polycystic Ovary Syndrome

        RDAs of Vitamin D Far Too Low

        Vitamin D and Tuberculosis

        Vitamin D For MS Patients