Vitamin D, an essential vitamin/hormone produced in the skin by ultraviolet radiation, is essential for calcium balance, bone density, immune function, and proper cell growth. Recent research suggests many individuals may be vitamin D deficient, especially those who do not get enough sun exposure, including people in northern latitudes.

Most vitamin D products on the market contain hidden preservatives. Thorne's D-1000 provides 1,000 I.U. per capsule of pure vitamin D, with no preservatives.