“The findings ... are a breakthrough of great medical and public health importance” (http://www.time.com, 8 June 2007). So said Cedric Garland, a prominent vitamin D researcher at the University of California-San Diego, speaking about a study published in the American Journal of Clinical Nutrition that suggests large doses of vitamin D may reduce the risk of cancer.

The 4-year US study involved 1,179 healthy post-menopausal women over the age of 55 in rural Nebraska. Researchers at the Creighton University School of Medicine in Omaha conducted a double-blind randomized placebo-controlled trial in which the study participants were randomly assigned to three groups who took 1,400–1,500 mg a day of supplemental calcium or supplemental calcium plus a 1,100 IU (international unit) dose of vitamin D per day (over twice the daily dose recommended by the US government), or placebo.

Women in the calcium plus vitamin D group had a 60% lower cancer risk over 4 years compared with the placebo group. After excluding the results in the first year to account for undiagnosed cancers that may have been present at the outset of the study, the calcium and vitamin D group showed a 77% lower cancer risk, whereas the researchers found no significant difference in risk for the calcium-only or placebo groups.

“The findings are very exciting. They confirm what a number of vitamin D proponents have suspected for some time”, said Joan Lappe, the lead researcher, adding that “vitamin D is a critical tool in fighting cancer” (http://www.medicalnewstoday.com, 8 June 2007).

However, Lappe cautions that more research is needed to confirm that the protective effect also applies to men, younger women and other ethnic groups. The American Cancer Society also reacted cautiously, pointing out that only 50 of the 1,179 women developed cancer, making broad conclusions difficult.