Dairy products and colorectal cancer. A review of possible mechanisms and epidemiological evidence

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Abstract
Objective: This review provides an overview of the principal hypotheses and epidemiological evidence of the possible links between colorectal cancer and intake of milk and/or dairy products. Methods: The first section outlines the main hypotheses about the possible effect of calcium, vitamin D, fats and other milk components. The possible role of acid lactic bateria in fermented products is also discussed. The second section is a summary of the published epidemiological evidence. The results on milk, cheese and yoghurt are summarized using a meta-analytical approach. The results of studies on calcium and vitamin D are briefly described. Results: Case–control studies are heterogeneous and, on average, do not provide evidence of association between total intake of total dairy products, milk, cheese or yoghurt and colorectal cancer risk. The average result from cohort studies support the hypothesis of a protective effect of total dairy products (odds ratio (OR): 0.62; 95% confidence interval (CI): 0.52–0.74; P heterogeneity test: 0.93) and for milk (OR: 0.80; 95% CI: 0.68–0.95; P heterogeneity: 0.77). No association was found between cheese (OR: 1.10; 95% CI: 0.88–1.36; P heterogeneity: 0.55) or yoghurt (OR: 1.03; 95% CI: 0.83–1.28; P heterogeneity: 0.69) in cohort studies. Conclusion: Cohort studies consistently found a protective effect of total dairy products and milk intake, but the evidence is not supported by case–control studies. No relationship was found with cheese or yoghurt intake. As the number of cohort studies is still limited, their results need to be confirmed by other prospective studies.