A new US study found that higher calcium intake was linked to a lower risk of total cancers in women only; and for both men and women, it was linked to lower risk of of cancers of the digestive system, and colorectal cancer in particular.
The study was the work of researchers from the National Cancer Institute in Bethesda, Maryland and the AARP in Washington, DC and was published online on February 23 in the Archives of Internal Medicine, one of the JAMA/Archives journals.
Previous studies have linked dairy food and calcium intakes to cancer risk but the results have been inconsistent and limited, and the effect on overall cancer risk is also unclear, wrote the authors in their background information.
They also wrote that calcium is known to be good for healthy bones and because of this the Institute of Medicine recommends adults aged 50 and over have 1,200 milligrams of calcium a day and the 2005 dietary guidelines for Americans says they should have 3 cups per day of low-fat or fat-free dairy foods.
For the study the authors analyzed data on 293,907 men and 198,903 women from the NIH-AARP Diet and Health and Study. NIH stands for National Institutes of Health and the AARP was formerly known as the American Association of Retired Persons.
When they enrolled in the study between 1995 and 1996 the participants had completed a food frequency questionnaire that asked them about the foods they ate and whether they took supplements. The researchers correlated their answers with state cancer registeries to identify new cancer cases from the start of the study until 2003.
Using a statistical tool called Cox proportional hazard they estimated the relative risks of individual and total cancers in men and women in relation to calcium intake.
The results showed that:
- During an average follow up of 7 years, there were 36,965 cases of cancer in the men and 16,605 in the women.
- There was no link between calcium intake and total cancer in men.
- There was a non-linear link between calcium intake and total cancer in women, and the risk went down as daily calcium intake went up to approximately 1,300 mg a day; no further risk reduction occurred above this level.
- In both men and women dairy food and calcium intake were inversely linked to cancers of the digestive system.
- Comparing the 20 per cent of participants who ate the most calcium (1,530 and 1,881 mg/day for men and women respectively) with the 20 per cent who ate the least (526 and 494 mg/day) showed a relative risk of cancer of the digestive system of 0.84 (16 per cent lower) for men and 0.77 for women (23 per cent lower).
- This decrease was even more pronounced for colorectal cancer.
- Calcium intake from supplements was also linked to lower colorectal cancer risk.
- Calcium and dairy food intake was not linked with prostate cancer, breast cancer or cancer in any other anatomical system besides the digestive system.
The authors concluded that:
“Our findings suggest that calcium intake consistent with current recommendations is associated with a lower risk of total cancer in women and cancers of the digestive system, especially colorectal cancer, in both men and women.”
The authors also wrote that dairy food is high in nutrients that are thought to have anti-cancer properties, these include calcium, vitamin D and conjugated linoleic acid. Also calcium has been shown to reduce abnormal growth and promote normal turnover of cells in the intestine and breast and it binds to bile and fatty acids, which is thought to reduce damage to the mucous membrane of the large intestine (includes the colon and the cecum).
The study was funded by the Intramural Research Program of the National Cancer Institute, which is part of the National Institutes of Health.
“Dairy Food, Calcium, and Risk of Cancer in the NIH-AARP Diet and Health Study.”
Yikyung Park; Michael F. Leitzmann; Amy F. Subar; Albert Hollenbeck; Arthur Schatzkin.
Arch Intern Med Vol. 169 No. 4, pp 391 – 401, February 23, 2009.
Sources: Journal abstract, JAMA and Archives Journals press statement.
Written by: Catharine Paddock, PhD