We used to think of vitamin D mainly as the cure for rickets, because in cod liver oil or fortified foods it did in fact cure this painful bone condition, which once afflicted the majority of children in Europe and North America. However, “vitamin” D controls up to 200 genes and helps regulate around 2000 genes overall. It is critical for building effective immunity. While 100-200 IU (or 2.5-5 mcg) of vitamin D daily was once thought adequate for preventing overt skeletal deformity, we now recognize greater requirements for it in overall health and immune function. Deficient or insufficient vitamin D activity, in the human body, translates into greater risk for infections, autoimmune disease, asthma, and for colon, prostate, breast, and overall cancer.
At one time, vitamin D deficiency was defined as serum levels of 25-hydroxy vitamin D below 20 ng/ml. It was later observed that crucial parathyroid hormone levels did not level out until serum vitamin D levels reached 30-40 ng/ml. At this point, vitamin D insufficiency was recognized as occurring at serum D levels of 21-29 ng/ml. By modern research estimates, the vitamin D status of over a billion human beings is likely either deficient or insufficient. Daily supplementation with 200, 400, or even 600 IU of vitamin D has not been found effective in raising serum vitamin D levels sufficiently to support long-term wellness.
As an endocrinologist concerned with epidemiology, Dr. Holick has long studied and contributed to the medical literature. This review distills his most urgent findings, which form the basis for his advice on raising national recommendations for daily vitamin D intakes. While this advocacy from Dr. Holick and others has succeeded in improving awareness of the enormous value of this inexpensive substance, many humans have yet to experience the vital immune and metabolic benefits of adequate vitamin D status.