Vitamin D cuts cancer risk, small study finds
High levels of vitamin D can reduce the incidence of cancer by 60%, according to a small study of older women in Nebraska published Thursday.
But the number of cancers observed in the four-year study, reported online in the American Journal of Clinical Nutrition, was small -- totaling only 50 -- leading some experts to question its conclusions.
The study, which tracked 1,179 subjects, also looked only at older white women, so it is not clear whether the findings apply to other population groups.
Dr. J. Leonard Lichtenfeld, deputy chief medical officer of the American Cancer Society, said the society found the results interesting but not sufficient to recommend that individuals increase their vitamin D intake.
Experience has shown, he said, that such reports about preventing cancer with a drug or vitamin did not pan out when they were subjected to randomized clinical trials. In this case, he said, the number of cancers observed was too small to be conclusive.
But Dr. Cedric Garland of the Moores Cancer Center at UC San Diego, who reported in 1989 that vitamin D reduces the incidence of colon cancer, said the results did not come out of left field.
Several large studies have suggested that vitamin D can reduce the risk of colon and breast cancers, and smaller studies have demonstrated a protective effect against prostate, lung and skin cancers.
The new study was conducted by Joan Lappe, a professor of medicine at the Creighton University School of Medicine in Omaha.
The women in the study had been free of cancer for at least 10 years at the start. Their average age was 67.
A third of the women in the study, which was designed to assess bone health, received daily calcium supplements plus 1,100 international units (IU) of vitamin D3, also known as cholecalciferol. Current guidelines for daily vitamin D consumption range from 200 to 600 IU, increasing with age.
Another third received only the calcium supplements, while the rest received a placebo.
After four years, the group receiving calcium and vitamin D had 13 cancers, while the group receiving calcium alone had 17, and the group receiving placebo had 20.
On the assumption that some of the women entering the study might have had a cancer at enrollment, the team looked at the last three years of the study. The results were more dramatic, with a 77% reduction in cancer risk. The women receiving vitamin D had eight cancers, the women receiving only calcium had 15, and the women receiving placebo had 18.
Most multivitamins contain vitamin D2 from plant sources. Vitamin D3, from meat sources, is generally considered to be more potent and is available separately as a supplement. Humans make their own vitamin D3 from exposure to sunlight.
Lichtenberg conceded that some people may want to increase their daily intake of vitamin D based on the study: “This should be done in consultation with a healthcare clinician, and in no case should exceed the recognized maximum safe dose of 2,000 IU per day.”
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