Dietary calcium was associated with significantly increased risk of prostate cancer in Chinese men with a below-average body mass index, according to an analysis of a large data set.
Researchers found that among subjects with a BMI below the median 22.9 kg/m
Data from previous studies have suggested a link between calcium and prostate cancer, but these studies have not been able to separate dairy products from calcium, said Lesley M. Butler, Ph.D., of Colorado State University in Fort Collins, and colleagues.
To more accurately assess the link between dietary calcium and prostate cancer, the researchers focused on a population of Chinese men whose dairy intake was relatively low. In general, Asian diets contain few dairy products, compared with Western diets, the researchers noted. Instead, most of the calcium in Asian diets comes from nondairy sources such as broccoli, kale, bok choy, and soy products. The researchers reviewed data from the Singapore Chinese Health Study, focusing on 27,293 men who did not have cancer when they entered the study between April 1993 and December 1998 (Cancer Res. 2010 June 1 [doi:10.1158/0008-5472.CAN-09-4544]).
Overall, dietary calcium was associated with a nonsignificant 25% increase in prostate cancer risk for the highest quartile of calcium intake (median of 659 mg/day) vs. the lowest quartile (median of 211 mg/day).
The study participants completed a 165-item food frequency questionnaire to assess their diets over the past year. Baseline characteristics including age, education, physical activity, and BMI were similar among the four quartiles.
Overall, the median daily intake of dairy products in the study population was 19.3 g. The greatest contributions of different food sources to daily calcium intake were vegetables (19.3%), dairy (17.3%), grain products (14.7%), soy products (11.8%), fruit (7.3%), and fish (6.2%). The variety of food sources suggest that the link between prostate cancer risk and calcium intake is not likely to be related to any particular food group, the researchers noted.
Neither age nor physical activity had an effect on the association between calcium and cancer, the researchers wrote.
“Our study is the first to report a positive association between calcium and prostate cancer risk at such a low calcium level,” the researchers said. Previous studies have shown that calcium is absorbed more efficiently in the Chinese population, compared with the white population, and among thinner people compared with heavier people, which is why a study of relatively thin Chinese men might be more likely to reveal a cancer/calcium connection than a study of heavier white men, the researchers wrote.
The study was limited by an inability to assess any variation of the calcium/cancer connection based on stage of disease, and more research is needed to evaluate the role of calcium in prostate cancer, compared with other components of dairy products, they added.
Disclosures: The study was supported by a grant from the National Cancer Institute. Dr. Butler reported having no financial conflicts.
My Take
Over 1,000 mg May Be Too Much
Previous studies indicated that high intakes of calcium (more than 1,000–1,500 mg/day) may increase prostate cancer risk. As there is no established benefit for men at such high intakes, it makes sense for men to not go much beyond the 1,000-mg/day range until further studies have been done. However, intakes of calcium that are too low (less than 700 mg/day) may increase risk of some conditions, such as hypertension and colorectal cancer. Thus, it is reasonable for men to be in the range of 700–1,000 mg/day, but prudent not to go too much lower.
These results need to be confirmed in other studies where calcium intake is relatively low and there are not many dairy products. Also, since many men take calcium supplements, that might be an informative group to study. Finally, men with prostate cancer need to be studied, as the results would be most pertinent to them.
In addition, the authors theorize that leaner men may absorb calcium better. The evidence for this is limited at this time. This could be a chance finding, so it also needs to be replicated in other populations.
EDWARD GIOVANNUCCI, M.D., is a professor of epidemiology and nutrition at Harvard University, Cambridge, Mass.
