Re: Prospective Studies of Dairy Product and Calcium Intakes and Prostate Cancer Risk: A Meta-Analysis

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Abstract
In their meta-analysis, Gao et al. ( 1 ) concluded that “High intake of dairy products and calcium may be associated with an increased risk of prostate cancer, although the increase appears to be small.” We report findings from the Melbourne Collaborative Cohort Study (MCCS), a prospective study of 41 528 people (17 049 men) who were 27–75 years old at baseline (99.3% were 40–69 years old). As previously described ( 2 , 3 ) , volunteers were recruited from November 26, 1990, to October 25, 1994, from among the residents of Melbourne, Australia. At baseline, subjects completed a questionnaire about potential risk factors for cancer as well as a food frequency questionnaire (FFQ) that was developed specifically for the MCCS ( 4 ) . In the FFQ, the dairy products category included milk, cheese, yogurt, cream, and custard. Butter and margarine were categorized separately. Calcium and energy intakes were calculated by using data from the FFQ, the mean sex-specific portion sizes from weighed food records, and Australian food composition tables ( 5 ) . Calcium density was calculated by dividing calcium intake by the total energy intake. After excluding 2407 men who did not complete the FFQ ( n = 35), who had a confirmed diagnosis of prostate cancer prior to baseline ( n = 105), who reported having a previous medical condition (i.e., self-reported angina, myocardial infarction, diabetes, hypertension, cancer, or stroke; n = 1928), or whose reported energy intake was in the lowest or highest 1% of the sex-specific distribution ( n = 339), 14 642 men were available for analysis. Incident cases of prostate cancer were ascertained through the state cancer registries in Australia; deaths were identified from state death records for Victoria and the Australian National Death Index. By the end of 2004, 23 men (fewer than 0.2%) were known to have left Australia and were considered lost to follow-up. Follow-up began at baseline and continued until the date of diagnosis of prostate cancer, of death, or of emigration from Australia or December 31, 2004, whichever came first.

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