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

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We thank Dr. Severi and colleagues for bringing their work to our attention. In their prospective study of 14 642 men, they note that neither dairy nor calcium intakes were statistically significantly associated with prostate cancer risk. We have repeated our meta-analysis to include this information. The revised pooled relative risk of prostate cancer for subjects in the highest relative to lowest dairy intake category decreased from 1.11 (95% confidence interval [CI] = 1.00 to 1.22, P = .047) to 1.09 (95% CI = 1.00 to 1.20, P = .059). For high versus low calcium intake, the pooled relative risk of prostate cancer decreased from 1.39 (95% CI = 1.09 to 1.77, P = .018) to 1.32 (95% CI = 1.05 to 1.67) but remained statistically significant ( P = .026). Although the association between high dairy intake and prostate cancer risk lost statistical significance, we cannot exclude the possibility of an association because the definitions of dairy intake varied among studies. Some studies included butter in their total dairy intake ( 1 ) , whereas some studies did not ( 2 , 3 ) , and this variation in exposure could affect the risk estimates. It is noteworthy that the population in the study by Severi et al. reported higher dairy intakes relative to those in most other studies ( 1 – 7 ) , with a median value for the lowest dairy category of 10 times/week. Because of the small number of completed studies and because both input variables and results vary among studies, further work in this area should be a priority.