Vitamin D
Vitamin D does not occur in plants, but some plants do contain compounds called sterols, which can be irradiated with ultraviolet light to make vitamin D. Yeast and fungi, for example, are major sources of ergosterol, which is irradiated artificially to make commercial vitamin D. The human skin contains another sterol, which is converted to vitamin D by the ultraviolet part of sunlight; unfortunately, modern life means relatively little exposure to sunlight for most people, besides daily bathing with soap which removes the skin's oil. Other natural sources are fish liver oils, milk, and egg yolk. Processed milk is generally fortified with additional vitamin D.
Vitamin D improves absorption and utilization of Calcium and Phosphorous; required for bone and teeth formation; maintains a stable nervous system and normal heart action.
A deficiency of Vitamin D may lead to rickets, tooth decay, softening of bones, improper healing of fractures, lack of vigor, muscular weakness, and/or inadequate absorption of calcium, retention of phosphorous in the kidneys.
Vitamin D is necessary for healthy bones and teeth, for proper assimilation and body balances of calcium and phosphorus, and for preventing rickets. It is fat-soluble and is not sensitive to heat, light, or oxygen.