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For a lot of reasons, the interest in vitamin D has been fiercely rekindled. The very active debate has arisen, to the point of being contentious at times, about how much is enough and for what other diseases it is beneficial besides maintaining bones.
Writings have reported that people have been aware of the substance we know now as vitamin D since early antiquity. The first vitamin D deficiency disease, rickets, was described both by Dr. Daniel Whistler in 1645 and professor Francis Glisson in 1650. In children primarily in urban areas, rickets was a lack of vitamin D, leading to soft, then permanently deformed bones, along with other symptoms, especially in nonsunny latitudes. Some thought it was due to lack of sunshine and fresh air, while others claimed a dietary factor was lacking. The major breakthrough came during the period of 1910-30 when nutrition as an experimental science blossomed, and many vitamins were discovered.
A broad definition of a vitamin is a substance that is essential for the maintenance of normal metabolic function, but is not synthesized in the body and must be supplied from an external source. We now accept the fact that vitamin D is a hormone with a steroid chemical skeleton, made primarily in skin by ultraviolet light converting incomplete vitamin D forms to more active forms that migrate to other tissues to function. By definition, a hormone is a substance secreted by a specific tissue and transported to a distance, where it exerts its effect on other specific tissues. Yet we can take plant vitamin D as a supplement, and it works. It might be mincing (munching?) words.
The work of Sir Edward Mellanby in 1919 and 1920 was the clincher to show both outdoors and diet were important to experimentally treat rickets in dogs. He raised dogs exclusively indoors, no sunshine or UV, and devised a diet that prevented rickets. In 1921 he wrote, “The action of fats in rickets is due to a vitamin or accessory food factor they contain, probably identical with the fat-soluble vitamin.” He also established that cod liver oil was an excellent anti-rickets agent. (Thanks a lot? Does anyone remember the “Our Gang” comedies where the evil woman was trying to chuck the equally evil cod liver oil down the kids’ throats?)
In 1923, Goldblatt and Soames clearly identified that when 7-dehydrocholesterol, a precursor of vitamin D in skin, was irradiated with sunlight or UV, a substance equivalent to the fat-soluble vitamin was produced. In differently designed studies, both Hess and Weinstock, and Steenbock and Black demonstrated that UV irradiation of food rations for rats protected them against rickets. The chemical structures of the vitamin “D’s” were determined in the laboratory of Professor A. Windaus in Germany. Ergosterol from plants could become vitamin D2, calciferol, after UV light exposure (1932), and 7-dehydrocholesterol turned into vitamin D3 after UV exposure (1936). Virtually at the same time, the active component of cod liver oil to remedy rickets was shown to be vitamin D3.
The story is still developing. The history of the vitamin D knowledge about bone metabolism, absorption from gut, interaction with kidney and its hormones and parathyroid hormone are all long, intricate sagas, often better than sleeping pills to read about. The newer knowledge of influencing type 1 diabetes, multiple sclerosis, some common cancers or rheumatoid arthritis is controversial, being researched (not mention searched), and will not be fully clarified for some time.
The idea of what is enough vitamin D also is undergoing a change, some argue unnecessarily. However, Dr. Hector Deluca at the University of Wisconsin, one of THE world’s vitamin D experts, has long advocated more vitamin D is needed than we produce or get. The counter is that hypervitaminosis, which causes bad side effects, is a potential reality, especially with fat-soluble vitamins.
Think about getting a little sun, but not to burn or wrinkle (Oops, the W word!). You can’t overdose on light. The discovery story is complete. The history is far from so. Maybe you don’t need to spend all your waking hours outdoors in a body bag. A little sun might not be a bad prescription after all, like a little chocolate.
