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© The Author 2006. Published by Oxford University Press.
CORRESPONDENCE |
RESPONSE: Re: Prospective Studies of Dairy Product and Calcium Intakes and Prostate Cancer Risk: A Meta-Analysis
Affiliations of authors: Harvard University School of Public Health, Boston, MA (XG); Boston University School of Public Health, Boston, MA (ML); Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA (KLT)
Correspondence to: Katherine L. Tucker, PhD,USDA HNRCA at Tufts Dietary Assessment & Epidemiology Research Program, 711 Washington St., Boston, MA 02111 (e-mail: katherine.tucker{at}tufts.edu).
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.
REFERENCES
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(2) Rodriguez C, McCullough ML, Mondul AM, Jacobs EJ, Fakhrabadi-Shokoohi D, Giovannucci EL, et al. Calcium, dairy products, and risk of prostate cancer in a prospective cohort of United States men. Cancer Epidemiol Biomarkers Prev 2003;12:597–603.
(3) Chan JM, Stampfer MJ, Ma J, Gann PH, Gaziano JM, Giovannucci EL. Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study. Am J Clin Nutr 2001;74:549–54.
(4) Tseng M, Breslow RA, Graubard BI, Ziegler RG. Dairy, calcium, and vitamin D intakes and prostate cancer risk in the National Health and Nutrition Examination Epidemiologic Follow-up Study cohort. Am J Clin Nutr 2005;81:1147–54.
(5) Hsing AW, McLaughlin JK, Schuman LM, Bjelke E, Gridley G, Wacholder S, et al. Diet, tobacco use, and fatal prostate cancer: results from the Lutheran Brotherhood Cohort Study. Cancer Res 1990;50:6836–40.
(6) Le Marchand L, Kolonel LN, Wilkens LR, Myers BC, Hirohata T. Animal fat consumption and prostate cancer: a prospective study in Hawaii. Epidemiology 1994;5:276–82.[ISI][Medline]
(7) Severson RK, Nomura AM, Grove JS, Stemmermann GN. A prospective study of demographics, diet, and prostate cancer among men of Japanese ancestry in Hawaii. Cancer Res 1989;49:1857–60.
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J Natl Cancer Inst 2006 98: 794-795.
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