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

Abstract

Objectives: 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. Conclusions: 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.

Dietary calcium, phosphorus, vitamin D, dairy products and the risk of colorectal adenoma and cancer among French women of the E3N-EPIC prospective study

“…Another review revealed a consistent protective effect of dairy products on colorectal cancer occurrence in cohort studies but not in case-control studies. 6 The effect was not found in the CPSN cohort. 9 The analysis of the Pooling Project 12 (which did not include the CPSN cohort) revealed a lower risk of colorectal cancer in subjects who consumed over 250 g/day of dairy products than in those consuming under 70 g/day.…”

“…2,3,6 Newmark et al 1 first suggested in 1984 that ionised calcium might precipitate with secondary bile acids and fatty acids to generate insoluble soap, protecting the mucosa from their deleterious effect. Later, others 33 suggested that phosphorus might also be involved in this mechanism through the formation of calcium phosphate.…”

“…As far as the effect of vitamin D is concerned, experimental studies have shown that 1a,25-dihydroxyvitamin D 3 might directly inhibit the proliferation of colonic cells and stimulate differentiation of a wide variety of cells, particularly colon cells, through the vitamin-D-receptor. 3 Some of these studies argued that the concentration of vitamin D receptors in cells might be greater than the levels of vitamin D. 3,6 Polymorphism of the vitamin D receptors could modulate the effect of both calcium and vitamin D. 3 Endogenous vitamin D synthesis is dependent on skin colour and sunshine exposure. Our data do not support a protective effect of dietary vitamin D. Further adjustment for sunshine exposure in our predominantly Caucasian population did not modify the findings.…”

“…5 However, findings from epidemiological studies on the relationship between calcium or dairy product intake and risk of colorectal adenoma or/and of cancer were judged inconsistent in 2 reviews, 6,7 except for a steady protective effect of dairy product reported in cohort studies. 6 Although a meta-analysis 8 concluded that calcium had no protective effect on colorectal tumours, prospective studies and large case-control studies subsequently found a modestly beneficial effect. [9][10][11] Recently the Pooling Project, a pooled analysis of 10 prospective studies, 12 showed a significant protective effect of calcium and milk on colorectal cancer risk.…”

“…2,4 It has been further suggested that polymorphisms of the vitamin D receptor (VDR) might modulate this effect. 5 However, findings from epidemiological studies on the relationship between calcium or dairy product intake and risk of colorectal adenoma or/and of cancer were judged inconsistent in 2 reviews, 6,7 except for a steady protective effect of dairy product reported in cohort studies. 6 Although a meta-analysis 8 concluded that calcium had no protective effect on colorectal tumours, prospective studies and large case-control studies subsequently found a modestly beneficial effect.…”