A 1000 IU dose of vitamin D2 daily was as effective as 1000 IU vitamin D3 in maintaining serum 25-hydroxyvitamin D levels and did not negatively influence serum 25-hydroxyvitamin D3 levels. Therefore, vitamin D2 is equally as effective as vitamin D3 in maintaining 25-hydroxyvitamin D status.

Vitamin D(2) and vitamin D(3) are equally bioavailable in orange juice and capsules.

Research over the last two to three decades has slowly demonstrated that Vitamin D, a long neglected and unappreciated hormone, is of profound importance to human health and survival. Vitamin D begins its synthesis in human skin with ultraviolet B radiation (UVB) from the sun. Melanin is a potent UVB blocker, protecting the skin from the high intensity sunlight found on the tropical savannah into which humans evolved, but not impairing the skin's ability to synthesize generous quantities of vitamin D there. Adaptation to environmental availability of UVB radiation from the sun appears to explain the variation in skin melanin content in indigenous human populations around the world. Evidence shows populations in the United States have mean vitamin D levels that are associated with the relative amount of melanin in the skin in those populations, and that humans with insufficient levels of vitamin D suffer disproportionately from the diseases associated with health disparities. The differences in incidence and severity of cardiovascular diseases, the most common cancers, diabetes, tuberculosis, conditions associated with infant mortality, and total mortality in populations associated with health disparities in the United States are explored in this chapter. Indeed, the magnitude of the disparity in diseases associated with ''health disparities,'' related to the effect of vitamin D on those diseases, is such that eliminating the differences in vitamin D levels between the populations would appear to virtually eliminate the health disparities between them.