A large cohort study spanning more than 20 years has demonstrated that increased calcium intake from all sources—dietary, supplemental, dairy, and nondairy—may be associated with reduced colorectal cancer risk across tumor sites.

In the study, published in JAMA Network Open, investigators analyzed data from 471,396 participants aged 50 to 71 years at baseline (1995 to 1996) in the National Institutes of Health–AARP Diet and Health Study. The participants in the highest quintile of total calcium intake had a 29% lower risk of colorectal cancer (CRC) compared with those in the lowest quintile (hazard ratio [HR] = 0.71, 95% confidence interval [CI] = 0.65–0.78, P < .001 for trend), with consistent results across calcium sources and tumor sites.

The study found that for each additional 300 mg of calcium consumed per day, there was an 8% decrease in overall CRC risk, a 10% decrease with dietary calcium, and a 5% decrease with supplemental calcium.

Mean total calcium intake in the lowest quintile was 401 mg per day among female participants and 407 mg per day among male participants, whereas the highest quintile averaged 2,056 mg per day among female participants and 1,773 mg per day among male participants. Dairy, nondairy, and supplemental sources contributed means of 42.1%, 34.2%, and 23.7% of total calcium intake, respectively.

The protective association was observed across anatomical sites, with total calcium intake linked to lower risk of proximal colon, distal colon, and rectal cancers.

Among non-Hispanic Black participants, who had lower overall calcium intake (382 mg per day in the lowest quintile vs 1916 mg per day in the highest quintile), dairy calcium intake was inversely associated with CRC risk (HR = 0.50, 95% CI = 0.32-0.80, P = .008 for trend); however, total calcium intake showed no statistically significant association (HR = 0.60, 95% CI = 0.32–1.13, P = .12 for trend).

During the median follow-up of 18.4 years, the investigators identified 10,618 incident first primary CRC cases among the study population, which was 59.5% male with a mean age of 62.0 years at baseline.

"Increasing calcium intake, especially among groups with lower consumption, may be associated with reductions in avoidable differences in CRC risk," the study authors concluded.

The authors declared having no competing interests.