Law and Order The jury is still out on the relationship between calcium intake and colorectal cancer risk. But a new study offers fresh and compelling evidence for the jury to consider.
Exhibit A Doctors Wei Zheng and Xiao-ou Shu of Vanderbilt University established the Shanghai Women's Health Study (SWHS) in collaboration with the National Cancer Institute and the Shanghai Cancer Institute. In the November 2006 issue of the International Journal of Cancer, Dr. Zheng, Dr. Shu, and their colleagues report on their most recent research to come out of the SWHS.
STUDY ABSTRACT - Researchers reviewed the dietary habits of more than 73,000 women whose average age was about 55
- During a follow up period of nearly six years, 283 cases of colorectal cancer were recorded
- When dietary data was compared to medical records, researchers determined that women who had the highest intake of calcium reduced their colorectal cancer risk by 40 percent compared to women with the lowest intake
- In their conclusion, the authors of the study wrote: "Our results suggest that calcium may be protective against colorectal cancer development even at a lower consumption level compared to Western populations."
Calcium-rich foods include salmon, cabbage, kale, and yellow, green, or waxed beans.
The Dartmouth case
The SWHS research adds significant dietary evidence to support previous studies that indicate the value of calcium supplements in preventing colorectal cancer.
In the e-Alert "Counting the Ways" (6/24/04), I told you about research from the Dartmouth-Hitchcock Medical Center. Researchers analyzed data collected from 930 patients enrolled in the Calcium Polyp Prevention Study. All of the study subjects had been diagnosed with colorectal polyps. Divided into two groups, participants received either a 1,200 mg daily supplement of calcium carbonate, or a placebo. Two colonoscopies were conducted approximately one year and four years after each subject's initial exams.
Researchers found that while calcium supplements appeared to provide some protection against the development of polyps, the supplements proved most effective against advanced polyps. The lead author of the study, Dr. John A. Baron told Health Day News that calcium may help lower the risk of advanced polyps by as much as 45 percent.
About one year later, Dr. Baron updated the 2004 study at a meeting of the American Association for Cancer Research.
The Dartmouth team followed up on more than 800 of the original 930 subjects and found that the protective effects of the calcium supplements appeared to continue for at least five years after the supplementation was discontinued. During those five years, polyp risk was reduced by more than 40 percent, and the risk of all colon cancers was reduced by 35 percent.
In previous e-Alerts, HSI Panelist Allan Spreen, M.D., has noted that sources of calcium are always accompanied by magnesium, so when supplementing with calcium, magnesium supplements should be taken as well. Foods high in magnesium include leafy green vegetables, whole grains, bananas, apricots, meat, beans, and nuts.
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