Calcium Rather Than Dairy Tracked With Lower Colorectal Cancer Risk in UK Women

CATEGORY: FOODS & NUTRIENTS

In a study that followed more than half a million women for over 16 years, each additional 300 milligrams of calcium a day—roughly the amount in a large glass of milk—was linked to a 17% lower risk of developing colorectal cancer.¹ Colorectal cancer is cancer of the colon or rectum, the last several feet of the digestive tract, and it is one of the most commonly diagnosed cancers worldwide. The link held whether the calcium came from dairy foods or from other sources.

12,251 Cancers Logged Over an Average 16.6 Years

The research drew on the Million Women Study, a long-running UK project that recruited women through breast-screening clinics. Some 542,778 of them answered a detailed questionnaire covering 97 separate dietary factors. What happened next is what gives the finding its weight: rather than asking the women years later whether they had been ill, the researchers linked their records to the NHS national cancer registry, which logs every cancer diagnosed in the country. Over an average of 16.6 years, 12,251 of them were diagnosed with colorectal cancer. Testing 97 factors at once would throw up false positives by chance, so the researchers raised the bar a finding had to clear; 17 factors survived it.

The signal came from calcium, not dairy itself

Several dairy-related items looked protective at first: milk, yogurt, riboflavin, phosphorus, magnesium, potassium. When the researchers accounted for calcium intake, those associations faded—which suggests dairy foods tracked with lower risk mainly because they are calcium-rich, not because of something else in them. Consistent with that, there was no meaningful difference between calcium from dairy and calcium from other foods.

Milk Gene Variants in Roughly 52,000 Cancer Cases

The team also used a technique that sidesteps the usual problem with diet studies. People inherit gene variants that nudge them toward drinking more or less milk, and those variants are dealt out at conception, independent of income, exercise or smoking. Comparing cancer rates across those inherited groups, in a dataset of roughly 52,000 colorectal cancer cases, again showed lower risk with more milk.

Alcohol Linked to 15% Higher Risk Per 20 Grams

Alcohol was the strongest factor in the other direction: each 20 grams a day, a little under two standard drinks, was linked to 15% higher risk. Red and processed meat together was linked to 8% higher risk per 30 grams a day, though neither held up separately. The authors note that equals 29% higher risk per 100 grams a day, substantially larger than the 12% reported in a 2018 pooled analysis.¹

Participants Were Overwhelmingly White British Women

This is observational research, so it shows association, not causation: women who ate more calcium may differ from those who ate less in ways the study could not fully account for. Diet was self-reported and captured mainly at one point in time. All the participants were women and overwhelmingly white British, and the authors note the results may not carry over to populations where most adults do not digest lactose well. The 17% is a difference in relative risk, not a personal probability, and it describes an average statistical pattern across the range of calcium intakes women in the study actually reported—the study does not identify a point above which additional calcium stops being linked to further risk difference, and it offers no basis for assuming that very high intakes would provide greater or complete protection.

Earlier Studies Put the Link at 8 Percent

A pooled reanalysis of earlier observational studies put the link at 8% lower colorectal cancer risk per extra 300 milligrams of calcium a day—about half the size found here.² And a trial that randomly assigned 2,259 people with recently removed precancerous growths to calcium supplements or a dummy pill found no drop in those growths returning over three to five years.³ Whether calcium taken as a pill behaves like calcium from food remains unsettled.

Key Takeaways

• Across 542,778 women followed an average of 16.6 years, each extra 300 mg of calcium a day was associated with 17% lower colorectal cancer risk, within the range of intakes the study observed.
• The association appeared to run through calcium itself rather than dairy foods, and did not differ by whether the calcium came from dairy.
• This is an observational finding—a strong and consistent one, supported by a separate genetic analysis, but not proof that calcium prevents colorectal cancer, and the study does not describe an upper limit beyond which more calcium would stop adding further benefit.

References

1. Papier K, Bradbury KE, Balkwill A, et al. Diet-wide analyses for risk of colorectal cancer: prospective study of 12,251 incident cases among 542,778 women in the UK. Nature Communications. 2025;16(1):375. link
2. Keum N, Aune D, Greenwood DC, et al. Calcium intake and colorectal cancer risk: dose-response meta-analysis of prospective observational studies. International Journal of Cancer. 2014;135(8):1940–1948. link.
3. Baron JA, Barry EL, Mott LA, et al. A trial of calcium and vitamin D for the prevention of colorectal adenomas. The New England Journal of Medicine. 2015;373(16):1519–1530. link.