Study Says Megadoses of Vitamin D Could Lower Risks of Various Cancers

By Jeffrey Tannenbaum

Ingesting about three times as much vitamin D as the norm may lower an individual’s risk of developing colon, breast or ovarian cancer, a study says.

Americans typically ingest 320 units a day of the vitamin, consisting of 200 units from food and 120 units from supplements. Daily intake of about 1,000 units may cut the odds of getting colon cancer by about half, and the chances of getting breast or ovarian cancer by about a third, according to the researchers.

Vitamin D supplementation could reduce cancer incidence and mortality “at low cost, with few or no adverse side effects,” the researchers said in an article appearing in the February 2006 issue of the American Journal of Public Health.

“The strongest effect is for colorectal cancer,” said lead author Cedric Garland, 59, an adjunct professor of family and preventive medicine at University of California at San Diego, in a telephone interview Tuesday. “There’s also a substantial effect for breast and ovarian cancer,” he said.

The substance involved is vitamin D3, usually called just vitamin D, although there is also a vitamin D2 that doesn’t have the same effects, Garland said.

The U.S. National Academy of Sciences recommends daily vitamin D intake of at least 200 units for adults 50 or under; 400 units at ages 51 to 70; and 600 units for people 71 or higher. The upper limit for safe intake is 2,000 units daily. Thus, the dose recommended by the researchers exceeds what most people now get and what the government recommends.

A glass of milk contains about 100 units of the vitamin, Garland said. While cod liver oil is rich in vitamin D, it also contains a lot of vitamin A, and the two vitamins compete for reception by the body, Garland said. He doesn’t recommend cod liver oil as a source of vitamin D.

To ensure getting 1,000 units of vitamin D, most people probably can take two 400-unit tablets, with the other 200 units coming from foods such as salmon, orange juice, yogurt and cheese, Garland said. Getting enough vitamin D through supplements would cost less than 5 cents a day, he said.

Although sunlight helps the body produce natural vitamin D, the researchers urged getting the minimum of 1,000 units through food and supplements. Dark-skinned people, because the need more sunlight to make vitamin D, are at increased risk of vitamin D deficiency, the scientists said.

The paper distills findings from 63 studies of how the vitamin relates of cancer risk. The journal is published by the Washington- based American Public Health Association.