Research indicates that a sufficient blood level of this hormone, vitamin D, is associated with fewer deaths from heart disease; breast, colon, and prostate cancer; hypertension, and the autoimmune conditions multiple sclerosis and type 1 diabetes. (Science tidbit: vitamin D is considered a hormone, because it can be manufactured in our bodies and it reaches our intestine via the blood stream to signal an increase in the absorption of calcium and phosphorus.)
An understanding of the role of vitamin D and concern over what appears to be a nationwide deficiency epidemic is increasing. In 2008, The American Journal of Clinical Nutrition reported the results of a study that looked at the vitamin D status of the U.S. population from 1988-1994 compared with 2000-2004. Overall, the researchers concluded that average blood levels of vitamin D had declined significantly from the earlier period — possibly related to changes in body mass, lower milk consumption, and the use of sunscreen.
With concern over their patients’ nutritional status growing, more doctors are testing blood levels of vitamin D (25-hydroxyvitamin D) levels and prescribing supplements.
Though the excitement over the positive health benefits of vitamin D seems warranted, some authorities have suggested that caution is in order. They point to the relatively few randomized clinical studies that have been performed and to the little that is known about optimal dosage levels. The issue of cause-and-effect is also in question. That is, healthy people typically have good levels of vitamin D — a positive correlation — but, there are likely to be other contributors, such as outdoor exercise and non-smoking, to their good health.