There have been many papers published on vitamin D. A Medline search for "vitamin D" will yield over 32,000 matches. It is well established that insufficient quantities of the vitamin contribute to osteopenia, osteomalacia, and osteoporosis. However, there is so much new interest in "boneless" applications of vitamin D that the topic was featured in the June, 2003 Reader's Digest.
Vitamin D was first isolated from tuna fish oil in 1936, and synthesized in 1952. It is a prohormone sterol which the body manufactures, given sunlight, from 7-dehydrocholesterol. Vitamin D 3 (C27H44O, cholecalciferol) is the form we and other animals make, and what is found in fish liver oil. Oddly enough, fish cannot synthesize vitamin D. They get theirs early in the food chain from planktonic algae, and big fish eat little fish, and we eat them.
Vitamin D 2 (C28H44O) is made from ergosterol, not cholesterol, and consequently is called ergocalciferol. This is the form that is found in plants, and that is also man-made by ultraviolet irradiation of ergosterol, and that is usually added to milk and found in most American supplements. Vitamin D3 is more commonly used as a supplement in Europe. As a curiosity, reindeer lichen contains both vitamin D2 and D3.
Although D2 and D3 differ by a single carbon atom, there is evidence that D3 is more efficiently utilized in chicks and, more to the point, in humans. "The assumption that vitamins D2 and D3 have equal nutritional value is probably wrong and should be reconsidered."
There are two commercial sources of natural vitamin D3: fish liver oil and an oil extracted from wool. "If a label lists 'vitamin D3 (cholecalciferol)' then it is from wool oil. This is considered a vegetarian source (the animal is not harmed, just sheared), but not vegan. Fish liver oil will be in parentheses if it is the source." Animals can obtain vitamin D from licking their fur, and in humans, rickets can be successfully treated by rubbing cod liver oil into the skin.
Scleroderma has responded favorably to long-term oral vitamin D3 (1,25-dihydroxycholecalciferol) therapy and psoriasis has been successfully treated, not only with vitamin D analogues, but with topical vitamin D3. Vitamin D deficiency may be a contributing cause of inflammatory bowel disease, and might be an effective treatment. Over 50 years ago, lupus vulgaris (tuberculosis of the skin) was reported successfully treated with 150,000 IU of vitamin D daily for six to eight months.
DEFICIENCY AND DIVERSITY: A SUMMARY
Vitamin D deficiency is cause or contributor to a wide variety of diseases, many of which appear unrelated to bone problems. So important is this vitamin for the entire population that it is necessary for milk to be enriched with it. Most persons do not get adequate vitamin D from sunlight, and the problem compounded for the obese and for the elderly. For those individuals, and for any person on any of a number of commonly prescribed medications, vitamin D supplementation is mandatory.
Government recommended dietary intakes of 200 to 600 IU/day are too low, according to the weight of clinical evidence. Government "tolerable" or "safe upper intake levels" (UL) of 1,000 to 2,000 IU/day are likewise too low, and largely unsupported by toxicological evidence. An optimum health recommendation of 1,000 to 4,000 IU/day, in total from all sources, is not unreasonable for the vast majority of healthy adults. Effective therapeutic levels for illness may be far higher. When high doses are used, appropriate testing and monitoring is recommended. It would be unreasonable to deny a therapeutic trial of vitamin D in cases of multiple sclerosis, scleroderma, psoriasis, congestive heart failure, hypertension, and various forms of cancer.
Excessive avoidance of sunlight, and sensational but unscientific dread of relatively high-dose vitamin D side effects does more than merely set the stage for a population of rickety children and fracture-ridden elderly. Overestimates and outright misstatements of vitamin D's "potential toxicity" open new marketing avenues for the development of vitamin D-like drugs, a commercial opportunity that the pharmaceutical industry has not overlooked.