A new Chinese study has found that calcium protects against cancer of the colon and rectum (colorectal). The Shanghai Women’s Health Study, from 1997 through 2000, enrolled 73,314 Chinese women aged 40 to 70, average age 55.5, who were living in urban Shanghai. Researchers followed up for an average of 5.7 years and, excluding the first two years of follow up, found that those with the highest amounts of calcium in the diet were 40% less likely to develop colorectal cancer than were those with the lowest dietary calcium. By the end of the follow up period, there were 129 reported cases of colon cancer and 91 reported cases of rectal cancer.
The study is significant because of the large number of participants and because the Chinese diet typically includes less calcium than does the Western diet. Previous large U.S. studies: the 1991 Women’s Health Initiative with 161,808 women, the 1976 Nurse’s Health Study I with 122,000 women, and the 1989 Nurse’s Health Study II with 125,000 women, did not report any link between calcium and colorectal cancer.
As in those studies, doctors in the Shanghai survey asked participants to fill out a food frequency questionnaire covering 77 foods representing 90% of the typical diet. Researchers also calculated the amounts in the diet of vitamins A, B1, B2, B3, C and E, as well as carotene and fiber, and found no link to risk for colorectal cancer. The scientists concluded that calcium appears to protect against colorectal cancer even at the relatively low levels in the Chinese diet compared to the Western diet. Colorectal cancer is one of the most curable cancer types, and doctors can diagnose the disease easily and early using a colonoscopy exam.