Milk, Calcium Intake Tied to Lower Colon Cancer Risk

Consumption of dairy products, particularly milk, had a significant association with a reduced risk of colorectal cancer (CRC) in women, data from a large British cohort study suggested.

For every 300 mg of daily calcium intake, the risk of CRC decreased by 17%, the strongest inverse association identified among almost 100 dietary factors analyzed. A genetics-based analysis of milk consumption reinforced a significant association with reduced CRC risk.

The study, involving data for 542,778 women, also corroborated a large volume of existing evidence linking alcohol consumption to a higher risk of CRC, reported Keren Papier, PhD, of the University of Oxford in England, and co-authors in Nature Communications.

“In this large prospective study of diet and colorectal cancer, we found a marked positive association for alcohol, and a strong inverse association for calcium,” the authors wrote. “Inverse associations were also observed with other dairy-related factors, including dairy milk, yogurt, riboflavin, magnesium, phosphorus, and potassium, which, on further analysis, appeared to be primarily due to the association of these dietary factors with calcium.”

“Further evidence for a potentially causal role for calcium in colorectal cancer incidence was provided by an accompanying analysis of genetically predicted milk intake, which is likely to also reflect calcium intake,” they added.

The study provided the strongest evidence to date of a protective effect of calcium on CRC risk, according to authorities on diet and cancer.

“This major study of over half a million U.K. women provides compelling evidence that dairy consumption, particularly milk and yogurt, is linked to reduced colorectal cancer risk, with the calcium in milk being a likely driver,” said Ian Givens, PhD, of the University of Reading in Berkshire, England. “The findings align with previous research and notably used genetic markers of milk consumption to strengthen the conclusions. What’s particularly concerning is that many U.K. women, especially younger age groups, are consuming less dairy and have calcium intakes below recommended levels.”

Although limited by the observational nature of the study, the results provide direction about dietary modifications that can reduce or increase the risk of CRC, noted Tom Sanders, DSc, PhD, of King’s College London.

“In my opinion, the take-home messages of this paper are that drinking above the safe limits of alcohol intake (more than 14 units/week) increases risk of colorectal cancer in women but that drinking about half a pint of cows’ milk a day (which would provide about 300 mg calcium) is probably protective,” he said.

Andrew Prentice, PhD, of the London School of Hygiene and Tropical Medicine, added that the “results emphasize that milk consumption is particularly beneficial and show evidence that this effect may be largely due to the calcium in milk, begging the question as to whether calcium supplements might be protective. The jury is out on this but as a nutritionist I shall continue to take my calcium from milk and dairy foods, which are rich in so many nutrients.”

For individuals who do not drink milk, the study identified other sources of calcium that may help lower the risk of CRC, such as broccoli or tofu, noted Lisa Wilde, PhD, of Bowel Cancer UK.

Despite numerous investigations, the role of dietary factors in CRC risk remains unclear, Papier and co-authors noted in their introduction. The International Agency for Research on Cancer classified alcohol and processed meat as carcinogenic and red meat as “probably carcinogenic,” partly on the basis of findings for CRC.

The third expert report from the World Cancer Research Fund/American Institute for Cancer Research also concluded that “convincing evidence” exists for associations between greater intake of alcohol and processed meat and increased risk of CRC, the authors continued. Additionally, the experts found that dairy products, dairy milk, calcium, calcium supplements, whole grains, and fiber-rich foods “probably” reduce the risk of CRC, and greater intake of red meat “probably” increases the risk.

In an effort to add clarity to relationships between dietary factors and CRC risk, the investigators performed a systematic analysis of 97 dietary factors and their association with CRC risk among 542,778 participants in the Million Women Study, which documented 12,251 cases of CRC during a mean follow-up of 16.6 years. All participants had completed a detailed dietary questionnaire, and 7% had also completed a 24-hour online dietary assessment.

The analysis identified 17 dietary factors with significant positive or negative associations with CRC (PPP

Consumption of red and processed meat also increased CRC risk. The remaining factors had negative associations with CRC risk, including dairy milk, phosphorus, riboflavin, whole grains, magnesium, yogurt, folate, carbohydrates, total sugars, vitamin C, fruit, breakfast cereal, potassium, and dietary fiber, which were associated with relative risk values of 0.07-0.83.

Papier and colleagues also performed a Mendelian randomization analysis of milk consumption, a statistical method that uses genetic variants to assess causal relationships. Based on data from three large population-based studies, the analysis showed that the risk of any CRC decreased by 40% with each 200 g/day consumption of dairy milk (95% CI 0.46-0.74), including by 40% for colon cancer (95% CI 0.43-0.77) and 51% for rectal cancer (95% CI 0.31-0.67).

“In addition to confirming the well-established positive associations of alcohol, and red and processed meat consumption, with risk of colorectal cancer, this large prospective analysis provides robust evidence supporting the protective role of dietary calcium,” the authors wrote in conclusion. “Additional research is needed to investigate overall health benefits or risks associated with higher calcium intakes.”

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