Extra Calcium May Reduce Colorectal Cancer Risk, NIH Study Finds

A new study of 471,000 adults shows benefit from both dietary and supplemental sources. 

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Adding more calcium to your diet could reduce colorectal cancer risk, the third leading cause of death in the United States, according to new research from the National Institutes of Health (NIH).

The benefit of adding more calcium to the diet held true regardless of the calcium source or the tumor’s location within the colon or rectum.

Dairy, Supplements, and Diet

Researchers surveyed 3.5 million members of the American Association of Retired People between the ages of 50 and 71, residing in six U.S. states and two metropolitan areas, between October 1995 and May 1996. “To our knowledge, this was the largest cohort study” examining the relationship between calcium intake and colorectal cancer risk, the researchers wrote.

After exclusions based on factors like preexisting cancer, poor health, or unreliable data, the final analysis included more than 470,000 people who were cancer-free at the start of the study.

The researchers in their discussion focused on two groups of participants: those who ingested about 400 mg of calcium daily and those who ingested about 2,000 mg per day. The second group’s calcium consumption exceeded the NIH’s current recommendation of 1,000 to 1,200 mg per day for people 19 and older.

Comparing people with the highest calcium intake to those with the lowest, the study found a lower risk of colorectal cancer in the former, according to the study results, published in JAMA Network Open.

This was true for calcium from all sources (8 percent lower risk), from food (16 percent lower risk), and from supplements (20 percent lower risk). For every extra 300 mg of calcium ingested daily, the risk correspondingly decreased.

One large glass of milk—about 8 ounces—provides around 300 mg of dietary calcium.

Dairy foods accounted for about 42 percent of total calcium intake, non-dairy foods about 34 percent, and supplements about 24 percent.

The study also found that in black people, the reductions in colorectal cancer risk were more pronounced, with decreases of 32 percent, 36 percent, and 19 percent, respectively, for each additional 300 mg of total calcium intake. African Americans have higher rates of colorectal cancer than other racial groups in the United States. This may be due to several factors, including socioeconomic status, health care access, and genetics.

Why Calcium May Show Benefit

The researchers don’t know exactly why calcium offers this benefit, but they have several theories.

One involves dairy calcium and its ability to bind to certain bile acids and fatty acids in the colon, potentially reducing their cancer-promoting effects. The researchers also noted that some dairy products contain vitamin D, which can improve calcium absorption in the digestive system.

The study authors also pointed to prior research indicating that the distal colon—a lower section of the large intestine that plays a role in the final stages of waste elimination and a common site for cancer development—has higher activity of the WNT signaling pathway. This network of proteins controls cell functions and is involved in cancer growth. The researchers said this makes the distal colon more receptive to calcium.

The researchers believe that the lower colon may be where calcium’s protection is strongest. They suggest that calcium may help cells grow properly in the colon, lowering the risk of cancer growth.

“Alongside keeping a healthy weight and stopping smoking, maintaining a healthy, balanced diet is one of the best ways to lower your risk of bowel cancer,” Sophia Lowes, senior health information manager for Cancer Research UK and not associated with the study, said in a statement.

“This includes cutting down on alcohol and red and processed meat, and eating lots of fruit, vegetables, and wholegrains.”

Good sources of calcium include dairy foods of all kinds, green leafy vegetables, and any food made with fortified flour.

Study Limitations

The authors acknowledged that the study was limited because dietary information was only collected at the beginning of the study, so they were unable to assess changes in calcium intake over time.

They also acknowledged the potential for inaccurate dietary data due to the reliance on self-reporting questionnaires.

Nonetheless, they emphasized that the size and scope of the study, along with its longer than 20-year follow-up period, provide strong evidence for a link between calcium intake and colorectal cancer risk, but add that further research in racial and ethnic minority populations is needed.