Traditionally, specific nutrient intake recommendations have been based on preventing a particular "index" disease--for instance, calcium to prevent osteoporosis or vitamin D to prevent rickets. However, researchers are now finding that nutrients are needed to prevent not only short-term disease but also many of the chronic, long-term diseases that are now facing the nation.
The "normal" ranges for many nutrients reflect their ability to ward of short-term disease only and may not be adequate to protect the body from long-term diseases such as cancer, heart disease and central nervous system degeneration.
Since these chronic diseases often show up much later in life, they are commonly attributed to non-nutritional causes. But, evidence suggests that nutrient deficiencies--even deficiencies that are viewed as slight by modern medicine standards--may be the cause of many chronic diseases.
One such nutrient deficiency is vitamin D. It was traditionally thought that a person had enough vitamin D as long as they didn’t have rickets or osteomalacia. Nutritional scientists have referred to 25(OH)D, the functional indicator for vitamin D, values of <20 nmol/L as "deficient", values above 80 as "normal," and values in between as "insufficient."
According to the author of the paper in the link below, Robert P Heaney, "Discerning the extent to which nutrition may play a role in such disorders [chronic diseases such as cancer, heart disease and central nervous system degeneration], positive or negative, is probably the principal challenge facing nutritional science today.
American Journal of Clinical Nutrition November, 2003;78(5):912-919
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.