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

CATEGORY: FOODS & NUTRIENTS

Milk and yogurt looked protective against colorectal cancer until the researchers accounted for calcium, and then the dairy signal faded. What stayed was calcium itself: each additional 300 milligrams a day, roughly the amount in a large glass of milk, was linked to a 17% lower risk of developing the disease, across more than half a million women followed over 16 years.¹ Colorectal cancer is cancer of the colon or rectum, the last several feet of the digestive tract, and one of the most commonly diagnosed cancers worldwide.

12,251 Cancers, Found in a Registry Rather Than a Follow-Up Survey

The work drew on the Million Women Study, a long-running UK project that recruited through breast-screening clinics. Some 542,778 women answered a detailed questionnaire covering 97 separate dietary factors. What happened next gives the finding its weight. Rather than asking the women years later whether they had been ill, 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 throws up false positives by chance, so the bar a finding had to clear was raised; 17 factors cleared it.

Calcium From Dairy and Calcium From Anything Else Behaved Alike

Several dairy-related items looked protective at first: milk, yogurt, riboflavin, phosphorus, magnesium, potassium. Accounting for calcium intake made those associations fade, which suggests dairy foods tracked with lower risk mainly because they are calcium-rich. Nothing else in them seemed to matter. Calcium from dairy and calcium from other foods showed no meaningful difference. The team then borrowed a technique that sidesteps the usual trouble 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 or 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 Ran the Other Direction

Alcohol was the strongest factor pointing the wrong way. Each 20 grams a day, a little under two standard drinks, was linked to 15% higher risk. Red and processed meat together tracked with 8% higher risk per 30 grams a day, though neither held up separately. The authors note that works out to 29% higher risk per 100 grams a day, substantially larger than the 12% reported in a 2018 pooled analysis.¹

What That 17% Does and Does Not Describe

This is observational research, so it shows association rather than 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. It was captured mainly at one point in time. The participants were all 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. It describes an average statistical pattern across the range of calcium intakes women in the study actually reported. No point emerges above which additional calcium stops being linked to further risk difference, and nothing here supports assuming that very high intakes would give greater or complete protection. A pooled reanalysis of earlier observational studies put the link at 8% lower risk per extra 300 milligrams a day, about half the size found here.² And a trial gave calcium supplements or a dummy pill, at random, to 2,259 people whose precancerous growths had recently been removed. Over three to five years the growths came back just as often either way.³ Whether calcium taken as a pill behaves like calcium from food is still unsettled.

Key Takeaways

• Each extra 300 mg of calcium a day was associated with 17% lower colorectal cancer risk, across 542,778 women followed an average of 16.6 years. That holds within the range of intakes the study observed.
• The association appeared to run through calcium rather than dairy foods, and calcium from dairy did not differ from calcium from other sources.
• A separate genetic analysis supported the link. Even so, this is an observational finding rather than proof that calcium prevents colorectal cancer, and no upper point was identified beyond which more calcium would stop adding 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.