Vitamin d metabolism pdf

They Could Save Your Health! Please also see my more recent and extensive article, From Seafood vitamin d metabolism pdf Sunshine: A New Understanding of Vitamin D Safety, as well as my article on vitamin D nutrition during pregnancy and lactation, Vitamin D in the Infant: Requirements and Safety. Also please see my blog posts about fat-soluble vitamins, in which I continually update my views. One of cholesterol’s many functions in the body is to act as a precursor to vitamin D.


Vitamin D can also be obtained from foods. Interestingly, foods that provide this vitamin — all of which are animal foods — tend to be high in cholesterol. Since cholesterol is a precursor to vitamin D, inhibiting the synthesis of cholesterol will also inhibit the synthesis of vitamin D. Since sunlight is required to turn cholesterol into vitamin D, avoiding the sun will likewise undermine our ability to synthesize vitamin D.

And since vitamin D-rich foods are also rich in cholesterol, low-cholesterol diets are inherently deficient in vitamin D. Vitamin D is best known for its role in calcium metabolism and bone health, but new roles are continually being discovered for it, including roles in mental health, blood sugar regulation, the immune system, and cancer prevention. Yet standard modern advice — take cholesterol-lowering drugs, avoid the sun, eat a low-cholesterol diet — combined with a recommended daily intake of vitamin D that is only a tenth of what many researchers believe to be sufficient all seems to pave the way for widespread vitamin D deficiency. Perhaps that’s why, according to Dr.

Are Plants and Irradiated Mushrooms a Source of Vitamin D? Do Cholesterol-Lowering Statins Inhibit Vitamin D Synthesis? Requirements: How Much Vitamin D Do We Need?

Toxicity: How Much is Too Much? When sunshine in the UV-B spectrum strikes the skin, it converts a substance in the skin called 7-dehydrocholesterol into vitamin D3. 7-dehydrocholesterol is a very close precursor to cholesterol. This conversion is actually believed to take more than 18 different steps and hasn’t been completely figured out, so it is usually simplified as one step.

When atmospheric conditions are ideal and skies are clear, 30 minutes of whole-body exposure of pale skin to sunlight without clothing or sunscreen can result in the synthesis of between 10,000 and 20,000 IU of vitamin D. These quantities of vitamin D are large, and therefore capable of supplying the body’s full needs. The availability of UV-B rays, however, depends on the angle at which sunshine strikes the earth, making vitamin D synthesis impossible for most people at most latitudes during parts of the year called the “vitamin D winter. Outside the vitamin D winter, sufficient UV-B rays for full vitamin D synthesis do not suddenly become available: the window of time during each day in which vitamin D synthesis can occur gradually expands as the season progresses, as does the amount of UV-B radiation available within that window.

Many different factors can make the availability of UV-B widely variable during any given time of the year. Clouds alone, for example, can eliminate up to 99 percent of UV-B radiation.