Colorectal cancer is the third most common cancer worldwide. Researchers have hypothesized that the different rates of colorectal cancer incidence in various countries may be related to diet. Although high calcium intake has been shown to inhibit colon cancer in animal experiments, these effects have not been seen consistently in human epidemiologic studies.
To better assess the relationship between consumption of dairy foods, calcium intake, and colorectal cancer risk, Eunyoung Cho, Sc.D., of Brigham and Women's Hospital and Harvard Medical School in Boston, and colleagues conducted a pooled analysis of 10 cohort studies from five countries. The studies included more than half a million individuals, among whom nearly 5,000 individuals were diagnosed with colorectal cancer during follow-up.
Among all of the food sources of calcium that the researchers examined, only milk consumption was associated with a decreased risk of colorectal cancer, particularly cancers of the distal colon and rectum. The risk decreased with increasing milk consumption; compared with people who consumed less than 70 grams/day (about 2.5 ounces) of milk, people who consumed 175-249 g/day (6.2-8.9 oz.) had a 12% reduction in risk of colorectal cancer and people who consumed more than 250 g/day (8.9 oz.) had a 15% reduction in risk. Each two 8-oz. glasses per day (500 g/day) increase in milk consumption was associated with a 12% decrease in risk.
The study also found that higher total calcium intake was associated with a decreased risk of colorectal cancer. Increasing calcium intake to 1000 mg/day or more could result in 15% fewer cases of colorectal cancer in women and 10% fewer cases in men, according to the authors.