Men also benefit from increased intakes of the mineral, with high intakes linked to a 16 per cent reduction in colorectal cancer risk, according to findings from the National Cancer Institute published in the Archives of Internal Medicine.
The researchers, led by Yikyung Park, arrived at the conclusions after analyzing data from 293,907 men and 198,903 women participating in the National Institutes of Health-AARP Diet and Health Study. The findings support the current US dietary guidelines to consume 1,200 milligrams of calcium for adults age 50 and older, and three cups per day of low-fat or fat-free dairy products.
"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," wrote Park and his co-workers.
The potential benefits for calcium, usually in combination with vitamin D mineral combination in relation to colorectal cancer is somewhat controversial, with some studies reporting benefits while others report null results.
Indeed, back in 2006 results from the Women's Health Initiative (WHI) stated that daily supplements of vitamin D and calcium 'had no effect' on the risk of colorectal cancer. The results were questioned however and independent cancer experts said at the time that the claims should be interpreted in the light of the complexities of the study.
Park and his co-workers analysed data from the NIH-AARP Diet and Health Study using food frequency questionnaires. The participants reported their consumption of dairy and other foods and their use of supplements.
They were subsequently followed for an average of seven years, during which 36,965 cases of cancer were diagnosed in men and 16,605 in women. While no association between calcium and the total risk of cancer was observed in men, the researchers noted that the risk decreased up to approximately 1300 mg/d, after which no further benefits were observed.
When the researchers considered only cancers of the digestive tract, both dairy food and calcium intakes in both men and women were associated with reduced risks.
Indeed, men with the highest average daily intakes of around 1,530 mg/d had a 16 per cent lower risk of these types of cancer, compared to men with the lowest average daily intakes of around 526 mg/d.
For women, the highest average intakes of calcium (1,881 mg/d) were associated with a 23 per cent lower risk of such cancers, compared to women with the lowest average intakes (494 mg/d). Furthermore, the decreased risk was particularly pronounced for colorectal cancer, said the researchers.
However, no association between calcium and dairy food intakes were observed for prostate, breast or any cancer in another anatomical system besides the digestive system, they added.
"Dairy food, which is relatively high in potentially anticarcinogenic nutrients such as calcium, vitamin D and conjugated linoleic acid, has been postulated to protect against the development of colorectal and breast cancer," wrote the authors.
The mechanism behind the potential benefits of calcium has not been fully elucidated with respect to cancer, but previous studies have reported that the mineral may reduce abnormal growth and induce normal turnover among cells in the gastrointestinal tract and breast. Additionally, it may also bind bile and fatty acids, thereby reducing damage to the mucous membrane in the large intestine, added the researchers.
Just one piece of the puzzle
The results were welcomed by Andrew Shao, PhD, vice president, scientific and regulatory affairs, for the Council for Responsible Nutrition (CRN), a supplements trade association.
“What this means for consumers is that there may be benefits to calcium supplementation that go beyond bone health; but more research is still needed to help explain the observed differences in gender and to better assess the effects on other non-digestive cancers,” said Dr. Shao.
“It’s also interesting to point out that the women in this study who had the highest calcium intakes - and lower risks of cancer - had lower body mass indexes, tended to be physically active, and were less likely to smoke cigarettes or drink alcohol.
This further reinforces the notion that good health is truly a combination of overall healthy practices - and vitamins and other supplements are an important part of that formula.”
Colorectal cancer accounts for nine per cent of new cancer cases every year worldwide. The highest incidence rates are in the developed world, while Asia and Africa have the lowest incidence rates.
Source: Archives of Internal Medicine2009, Volume 169, Issue 4, Pages 391-401“Dairy Food, Calcium, and Risk of Cancer in the NIH-AARP Diet and Health Study”Authors: Y. Park, M.F. Leitzmann, A.F. Subar, A. Hollenbeck, A. Schatzkin