© 2004 by Oxford University Press
© 2004 Oxford University Press
CORRESPONDENCE |
RESPONSE: Re: Research and Public Health Implications of the Intricate Relationship Between Calcium and Vitamin D in the Prevention of Colorectal Neoplasia
Correspondence to: Elizabeth T. Jacobs, PhD, Arizona Cancer Center, P.O. Box 245024, Tucson, AZ 85724-5024 (e-mail: jacobse{at}u.arizona.edu)
We thank Dr. Heaney for his interest in our editorial. However, there are several points in his commentary that we believe are misleading with regard to the epidemiologic data related to dairy products, calcium, and prostate cancer.
First, data from the Health Professionals Follow-up Study showing that higher daily intake is associated with an increased risk of prostate cancer are now supported by more than a dozen studies, as discussed by Rodriguez et al. in a recent publication from the Cancer Prevention Study II Nutrition Cohort (1), which also showed a statistically significantly increased risk for prostate cancer associated with higher calcium intake (1). Dr. Heaney states that, in the work of Michaud et al. (2), the effect of calcium on prostate cancer has disappeared as new cases have accumulated. We strongly disagree with the interpretation of these data. First, Michaud et al. (2) did not address the association between calcium itself and prostate cancer but rather the effect of animal products; calcium appeared only as a covariate in the multivariable models. Although the association of dairy products themselves with the risk of prostate cancer was no longer statistically significant, this result occurred after controlling for calcium and fat in the regression model. This finding, therefore, actually supports a potential detrimental role for calcium in prostate cancer risk. Indeed, the authors of this work themselves conclude that these findings may explain the previously observed positive association between dairy products and prostate cancer (2).
Further, Dr. Heaney references the analyses by Wallace et al. (3) to indicate that calcium supplementation may offer protection from prostate cancer. Although a suggestion of reduced risk of prostate cancer with calcium supplementation was indeed observed in this study, caution should be used when drawing conclusions from these data (3). The results were not statistically significant (P = .09), and the original trial was designed to test the effect of calcium supplementation on colorectal adenoma recurrence, not prostate cancer. In addition, because the duration of this study was relatively short, most of the prostate cancers were probably early-stage cancers. This is relevant because studies have indicated that higher calcium consumption may be more strongly associated with later-stage cancers (1,4). It is possible that calcium has differential effects on prostate cancer depending on the stage of the disease. Therefore, after weighing the evidence, we believe that our conclusion of exerting caution when developing public health recommendations for increased consumption of calcium or dairy products is justified.
We do agree with Dr. Heaney that several health benefits are associated with dairy foods. Despite his assertion that we are "excluding a major food group" and did so "out of hand," in no way did we suggest the elimination of dairy products from the diet. We merely noted that there are alternatives to dairy for obtaining calcium and that increasing intake of dairy may not be the best recommendation, given the potential adverse effects on prostate cancer. For this reason, we also discussed whether increasing calcium intake at all would be an important public health message. We believe that further research is necessary to more clearly define the appropriate dose and type of calcium for optimal health.
REFERENCES
1 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.
2 Michaud DS, Augustsson K, Rimm EB, Stampfer MJ, Willet WC, Giovannucci E. A prospective study on intake of animal products and risk of prostate cancer. Cancer Causes Control 2001;12:557–67.[CrossRef][ISI][Medline]
3 Wallace K, Pearson LH, Beach ML, Mott LA, Baron JA. Calcium supplementation and prostate cancer risk: a randomized analysis [abstract 2479]. Proceedings of the American Association for Cancer Research; 2001 Mar 24–28; New Orleans (LA): American Association for Cancer Research; 2001. p. 260.
4 Giovannucci E, Rimm EB, Wolk A, Ascherio A, Stampfer MJ, Colditz GA, et al. Calcium and fructose intake in relation to risk of prostate cancer. Cancer Res 1998;58:442–7.
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J Natl Cancer Inst 2004 96: 805-806.
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