Vitamin D is not one chemical but many. The natural form is produced in the skin from a universally present form of cholesterol, 7-dehydrocholesterol, or D3. Sunlight is the key.
Vitamin D’s major role is to keep bones healthy by increasing the intestinal absorption of calcium; without enough vitamin D the body can’t absorb the calcium it needs. Researchers have begun to suspect that vitamin D may do even more.
When it’s added to human cells being grown in the laboratory, it promotes normal cell maturation and reduces abnormal cell multiplication. As a result, doctors wonder if vitamin D may have a role in preventing cancer. For example, in test tube and animal experiments, vitamin D can slow the growth of prostate cancer. The disease is more common in North America and northern Europe than in the sunnier climates of Asia, Central America and Africa.
Until recently the recommended daily allowance of vitamin D was just 200 international units, which is still considered adequate for people younger than 50. For 51- to 70-year-olds, however, the adequate daily dose is now pegged at 400 I.U.’and some experts go even further, recommending 800 I.U. per day. The average multivitamin contains 400 I.U. of vitamin D, so for most men a daily multivitamin is a good bet, but be sure to get enough calcium too.
‘Harvard Men’s Health Watch, February 2001
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