Vitamin D sufficiency is required for optimal health. The conditions with strong evidence for a protective effect of
vitamin D include several
bone diseases,
muscle weakness, more than a dozen types of internal
cancers,
multiple sclerosis, and
type 1 diabetes mellitus. There is also weaker evidence for several other diseases and conditions. There are good reasons that
vitamin D sufficiency be maintained during all stages of life, from fetal development to old age. Adequate
calcium intake is also recommended. The current
vitamin D requirements in the United States are based on protection against
bone diseases. These guidelines are being revised upward in light of new findings, especially for soft-tissue health. The consensus of scientific understanding appears to be that
vitamin D deficiency is reached for serum
25-hydroxyvitamin D (25OHD) levels less than 20 ng/mL (50 nmol/L), insufficiency in the range from 20-32 ng/mL, and sufficiency in the range from 33-80 ng/mL, with normal in sunny countries 54-90 ng/mL, and excess greater than 100 ng/mL. Solar ultraviolet-B (UVB) irradiation is the primary source of
vitamin D for most people. In general, the health benefits accruing from moderate UV irradiation, without
erythema or excess tanning, greatly outweigh the health risks, with skin pigmentation (
melanin) providing much of the protection. In the absence of adequate solar UVB irradiation due to season, latitude, or lifestyle,
vitamin D can be obtained from fortified food, oily fish,
vitamin D supplements, and artificial sources of UVB radiation.