Major food sources of calcium in this population consisted of: vegetables (19.3 percent), dairy (17.3 percent), grain products (14.7 percent), soyfoods (11.8 percent), fruit (7.3 percent) and fish (6.2 percent). However, the researchers stress that there was no positive association with prostate cancer risk and any one particular food source.

Among men with less than average BMI (median BMI was 22.9 kg/m2), the researchers found a twofold increased risk of prostate cancer.

"It was somewhat surprising that our finding was consistent with previous studies because nearly all of them were conducted among Western populations with diets relatively high in calcium and primarily from dairy food sources," Butler said. Edward Giovannucci, M.D., Sc.D., professor of epidemiology and nutrition at Harvard School of Public Health, who is not associated with this study, said these results add more evidence that calcium is a causative factor of prostate cancer.

"However, there are some aspects that require further study," he said. "First, they found an association with relatively low intakes of calcium, whereas most previous studies suggested an association with high intake of calcium. Also, they found an association mostly in lean men, and whether this is true or is a chance finding requires further study."

Additional studies are needed to explore the possible roles of calcium, as opposed to other dairy product components, in prostate cancer progression, Butler stressed.

SOURCE Cancer Research