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Colon Cancer

Synopsis

The components in milk products that may be responsible for the beneficial effects include: calcium, vitamin D, butyric acid, sphingolipids and conjugated linoleic acid (CLA). The impact may be different at different sites along the colon and rectum, with more of an impact being demonstrated along the colon.

The Evidence

According to the report from the World Cancer Research Fund and the American Institute for Cancer Research on the role of diet and lifestyle on prevention of cancer, there is sufficient evidence to conclude that milk probably protects against colorectal cancer.¹

A meta-analysis conducted in 2009 that consisted of 60 epidemiological studies among adult men and women also revealed that higher milk product consumption reduces the risk of colon cancer.² A relative risk (RR) was calculated for the highest compared to the lowest milk product intake categories. The data showed that those with high intakes of milk (all types) had, on average, a significant 22% reduction in colon cancer risk.² As for other milk products, there was a significant 16% risk reduction of colon cancer.²

Similarly, a large prospective cohort study of more than 36,000 adult men and women (ages 50 to 71 years) demonstrated that milk products as well as total dietary calcium intake significantly reduced the risk of colorectal cancer in both women and men.³ The relative risk for milk product consumption in the highest compared to the lowest quintile of intake was 0.72 (p_trend < 0.01) and 0.85 (p_trend = 0.01) for women and men, respectively.³

A pooled analysis of 10 prospective cohort studies in five countries demonstrated that higher consumption of milk (high and low fat), dietary calcium and total calcium (food and supplements) is associated with a lower risk of colorectal cancer.⁴ These studies followed the milk product consumption habits of 534,536 individuals for up to 6 to 16 years of follow-up. The data showed the following:

• Those who drank at least one glass of milk (250 ml) per day were 15% less likely to develop colorectal cancer than those who drank little (< 70 ml/day) or no milk (p_trend < 0.001);
• Each 500 ml-per-day increase in milk intake (about two glasses) was associated with a 12% reduced rate of colorectal cancer risk;
• The inverse association between milk intake and colorectal cancer risk was limited to cancers of the distal colon and rectum;
• The authors also measured the independent effects of calcium and vitamin D intake and found that the relative risk was lowest (RR = 0.74) for persons in the highest category of both total calcium and total vitamin D intake compared with the lowest category of intake for both nutrients.

The studies conducted thus far have been in the context of a more western dietary pattern and lifestyle. Results published in 2009 from a large prospective cohort study of 73,224 women (40 to 70 years old) from 7 urban communities in Shanghai China, also demonstrated that milk intake was significantly inversely associated with the risk of colon cancer (RR= 0.8, p_trend=0.05) whose incidence is rapidly rising in that country.⁵ Also, there were no associations found between meat and fat intake and risk for developing colorectal cancer.⁵

The evidence thus far suggests a differential effect at different colorectal sites. For example, in a cohort of Swedish men, milk was the milk product with the strongest impact on colorectal cancer risk, and the distal colon was the segment most affected (RR=0.53, p=0.01).⁶ Dietary calcium had an effect at different sites than those of milk products. Indeed dietary calcium impacted the rectum and possibly the proximal colon, whereas total milk products had an impact on the proximal colon and milk, sour cream and cream on the distal colon.⁴ The association between total milk products and the risk of colon cancer appeared to be only partly explained by calcium, indicating that other components may also play a role.

Potential Mechanisms

The mechanisms by which milk products and/or components reduce the risk of colon cancer have yet to be elucidated. However, several components in milk products are believed to be involved such as:⁷

• Calcium,
• Vitamin D,
• Butyric acid,
• Sphingolipids,
• Probiotics,
• Conjugated linoleic acid (CLA) found in dairy fat.

A 4-year, randomized, double-blind, placebo-controlled trial of 803 men and women (mean age 61 years) has shown that calcium supplementation and vitamin D status appear to act in synergy to reduce the risk of colorectal adenoma recurrence.⁸

A study using the Swedish Mammography Cohort (n = 60,708 women aged 40-76 years) has demonstrated an inverse relationship between milk products and colorectal cancer, particularly of the distal colon.⁸ Dairy fat containing CLA appeared to be the important factor, and consumption of cheese (which represented half the milk product intake in that study) conferred the lowest risk of colorectal cancer.⁹

• A multivariate analysis showed that women who consumed 4 servings or more per day of high-fat dairy foods were significantly less likely to develop colorectal cancer than those consuming less than 1 serving;
• Each daily increment of 2 servings of high-fat milk products corresponded to a 13% reduction in the risk of colorectal cancer and a 34% decrease in the risk of distal colon cancer;
• CLA intake was significantly associated with reduced colorectal cancer risk and the association was strongest for distal colon cancer;
• These reductions persisted after controlling for calcium and vitamin D intakes.

Conclusions

There is consistent and very good evidence to suggest that milk and milk products may significantly reduce the risk of developing colon cancer.

Randomized, controlled trials and mechanistic studies are needed to provide more definitive answers.

Keywords: colon cancer, cancer prevention

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