Prostate cancer is a common form of cancer in America and a major contributor to cancer-related deaths.1 Investigations into dietary risk factors of prostate cancer over the recent years have only identified few related factors. Several researchers concur that the consumption of dairy products, which is the main source of calcium in western diets, is positively linked to prostate cancer.2,3 Other products such as meat, fat, tomato, or lycopene are also associated with the high risks of prostate cancer. Research findings also indicate that nations with increased consumption of dairy products have increased incidences of prostate cancer than those with limited consumption trends.4 The progression of research deserves critical review to understand why few factors have been established from the bulk of dietary risk factors in the recent decades. Of specific interest in this study is the progression of studies on whether calcium or dairy intake affects the risk of prostate cancer and whether the associations are true.

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To investigate the effect of dairy products and calcium intake on the risks of prostate cancer, a systematic review of studies was initiated to analyze the relationship between exposure to elements and disease progression. The review was achieved by comparing research on the risks of disease exposure in groups to factors such as high dietary intake of calcium and dairy products. The trends in the studies were also examined by studying the categories of nutrients and the types of tests employed. Data identifying the relationship were pooled together to aid in the primary analysis of dairy product and calcium intakes on increased risks of prostate cancer. I was evident that epidemiologic studies reporting relative risks of prostate cancer compared low and high dietary intake of dairy products.5,6,7 The findings support that dairy products are the major source of calcium and the greatest enablers of prostate cancer development as it down-regulates the production of 1,25-dihydroxyvitamin D3, which is a hormone protecting against prostate cancer. The positive association formed the baseline of this study to identify research refuting or backing the claim.

A prospective multivariate analysis of prostate cancer progression was limited to the study of cancer supplements only.5,8,9 The relationship strongly indicated that calcium rather than several other dairy products increased the risk of prostate cancer. A similar Swedish control study revealed a strong relationship between calcium and advanced or metastatic prostate cancer.10 Contrastively, a baseline dietary data study from Finland showed that calcium intake was not positively related to increased risks of prostate cancer.11 However, the study findings showed that among the participants with high calcium intake, the risks of prostate cancer was high. Similarly, a cohort study from Netherlands shows that milk products have a positive trend and not calcium.12

Conversely, case-control studies from American, Greek, and Japanese populations failed to find a definite relationship between dietary calcium and the increased risks of prostate cancer whereas a case-control study of Serbia revealed an inverse trend in calcium and prostate cancer risks.7,10, 13 A case-control study of the United States also revealed no association between the use of calcium supplements and the increased risks of cancer.1 From the summarized findings of various studies, it is evident that results identifying a positive relationship between calcium or dairy intake and prostate cancer risks are only suggestive, yet limited and conflicting. The findings make it more necessary to investigate the impact of dairy products and dietary calcium intake on the risks of prostate cancer among populations.

The results of the pooled studies are consistent with previous findings supporting the inconclusiveness of the hypothesis that dairy products and calcium are positively linked to increased risks of prostate cancer.14 However, the inconclusive findings can be attributed to several design issues in the research studies. For example, the inability of researchers to control the total energy in control studies introduces little or no bias. Similarly, a design issue such as random misclassification of calcium and dairy product exposure is linked to incomplete dairy calcium assessments that encourage underestimations of the true relationship.1,15 The absence of information on calcium drawn from non-dairy products such as vegetables is another concern. Next, the findings cannot be categorized as extreme given that information on supplemental calcium intake is limited in the studies.7 The concern adds to the amount of misclassification in several studies and may result in underestimations of the association. Last, the significant relationship between dairy products and calcium intake make it impossible to account for other dairy food elements such as dairy fat as contributors to the observed relationships.

In sum, the results of this report extend and support previous observations that the study on high intake of dairy products and calcium in diets and its association to high prostate cancer risks are inconclusive. The findings complicate the generalization of results indicating that high calcium or dairy intake affect the risk of prostate cancer. The findings interject caution on the interpretation and promotion of higher calcium intake among populations. Additional prospective studies of the research question are needed as part of the comprehensive review of dietary and supplement calcium use. The findings of the research support that health professionals need to re-evaluate evidence on dietary intake recommendations of calcium and dairy products if they are to ensure that the public abstains from increased exposure to prostate cancer.

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