Study points to puzzle of calcium/cancer link
say the authors of a new study into the link between dairy products
and the disease. But as Jess Halliday reports, previous
research suggesting that low fat sources of the mineral could help
protect against colorectal cancer means further investigation into
its action is needed.
A study carried out at Fox Chase Cancer Center in Philadelphia and published in this month's American Journal of Clinical Nutrition set out to examine the link between prostate cancer and consumption of dairy products, calcium and vitamin D.
Led by Marilyn Tseng, the researchers drew their data from the National Health and Nutrition Examination Epidemiologic Follow-up Study, which took place between 1982-4 and 1994 and involved 3612 men.
Amongst the participants, 131 cases of prostate cancer were identified. Tseng's team compared dietary questionnaires completed at the start of the study by men who developed cancer with those completed by men who did not. They estimated relative risk (RR) and 95 percent confident intervals (CIs) using age-, race-, and other covariant-adjusted Cox proportional hazards models.
Dietary calcium was seen to be strongly associated with an increased risk of prostate cancer, with the highest consuming tertile having a RR of 2.2 compared with the least consuming tertile, and a 95% CI of 3.5 compared with 1.4.
Overall intake of dairy products showed the same 2.2 rate of RR between the tertiles and 95% CI of 3.9 compared with 1.2.
But while low-fat milk showed some increased risk (RR of the third tertile over the first was 1.5 and 95% CI 2.2 compared with 1.1), no real increase was seen in whole milk consumers, where RR was 0.8 and 95% CI was 1.3 compared with 0.5.
Neither vitamin D nor phosphorus was clearly associated with increased risk.
Previous evidence indicating a reduced risk of colorectal cancer with higher calcium consumption includes a study published in Cancer Epidemiology, Biomarkers and Prevention (vol 14, pp126-132) in January, which showed that women who consumed in excess of 800mg of calcium each day could cut their risk of developing colorectal cancer by up to 46 percent. Deriving calcium from both diet and supplements was seen to double the risk reduction observed when it came from either source alone.
These findings appeared to confirm the conclusions drawn last year by researchers from the Brigham and Women's Hospital in the US, who analyzed the results of studies carried out in five different countries and involving around half a million people, 5000 of whom developed bowel cancer.
They found that people with a milk intake between 70g and 174g had a 6 per cent lower risk of colorectal cancer than those consuming less than 70g. The risk decreased to 12 per cent for those with a daily intake of up to 249g, and to 15 per cent for those with an intake of more than 250g.
The Fox Chase scientists are not the first to draw attention to the seemingly duplicitous relationship between calcium and cancer. A body of evidence on the subject, which their results bolster, led them to conclude that "the mechanisms by which dairy and calcium might increase prostate cancer risk should be clarified and confirmed".
