Study: Vitamin D cuts cancer risk

OMAHA, Neb. — Vitamin D cut the risk of several types of cancer by nearly 60 percent overall for older women, in the most rigorous study yet.

The new research strengthens some specialists' argument that vitamin D may be a powerful cancer preventative and that most people should get more of it. Experts remain split, though, on how much to take.

"The findings ... are a breakthrough of great medical and public-health importance," said Cedric Garland, a prominent vitamin D researcher at the University of California, San Diego. "No other method to prevent cancer has been identified that has such a powerful impact."

Although the study seemed the most reliable yet, it does have drawbacks. It was designed mainly to monitor how calcium and vitamin D improve bone health, and the number of cancer cases overall was small, showing up in just 50 patients.

"It's a very small study," said Dr. Edward Giovannucci, who researches nutrition and cancer at the Harvard School of Public Health. "I don't think it's the last word."

In either case, the study takes an important step in extending several decades of research that began with observations that cancer rates among similar groups of people were lower in southern latitudes than in northern ones. Scientists reasoned that had to do with more direct sunlight in southern regions.

The skin makes vitamin D when exposed to sunlight's ultraviolet rays. This study used that same form of the vitamin, known as D{-3} or cholecalciferol. Multivitamins usually carry a much weaker variant known as D{-2}, but D{-3} is available in stand-alone dietary supplements.

Earlier research has shown that vitamin D helps regulate cell growth, a fundamental biological process that goes haywire in cancer.

This study, published today in the American Journal of Clinical Nutrition, is the first time that researchers significantly boosted — and measured — blood levels of vitamin D and then followed identical groups of patients from start to finish.

That's why, despite its modest size, the research was generating excitement. Nearly all other work has compared disparate groups of patients.

The researchers at Creighton University in Omaha focused on 1,179 seemingly healthy women with an average age of 67. The women were divided into three groups: 446 got calcium and vitamin D{-3} supplements, a similar number got calcium alone, and 288 took a placebo.

The research team gave 1,000 daily international units of vitamin D, more than current guidelines calling for 200 to 600 units depending on a person's age.

The researchers intended to check mainly for the effects of calcium on bone health. Their interest in cancer risk was secondary.

But the lower cancer risk stood out. Only 13 women, or 3 percent, developed cancer over four years of calcium and vitamin D supplements. With calcium alone, 17 women, or 4 percent, got cancer. With the placebo, cancer appeared in 20 women, or 7 percent.

That shows a 57 percent lower cancer risk over four years in the group taking both supplements, compared with patients taking a placebo. And when the first-year cancers were excluded — the ones mostly likely present before the study began — the findings were stronger still: a 77 percent lower risk for the combo group.

While the calcium-only group lowered its four-year cancer risk by 43 percent compared with the untreated group, it did no better when early cancers were excluded. That suggests calcium alone may have done little in this experiment, the researchers said.

Experts reviewing the study focused on vitamin D as the powerful agent in the combo group, but it can't be ruled out that calcium might somehow amplify the effect of vitamin D.

Dr. Michael Holick, of Boston University Medical Center, who sat on the professional panel that issued the 1997 guidelines for vitamin D, said this study shows that enough vitamin D "markedly reduces the risk of developing the most serious deadly cancers." He supports raising the recommended amount of the vitamin and said 1,000 daily units of vitamin D{-3} would now be reasonable for most people.

Joan Lappe, the study's lead researcher, said it "just adds to the great bunch of evidence that we need to have better vitamin D nutrition." Some foods carry the vitamin, such as salmon, tuna and fortified milk, but diet accounts for little of the vitamin circulating in the body. Overexposure to the sun, however, can cause skin cancer.

Information in this article, originally published June 8, was corrected June 11. In a previous version of this story, the Associated Press reported that an American Cancer Society doctor favors keeping current vitamin D guidelines of 200 to 600 international units daily. Dr. Michael Thun said he misunderstood a question and holds no position on whether those amounts should be changed. He also said he thinks it's too early to recommend using vitamin D to prevent cancer.