Polyps are small growths in the colon. They are non-cancerous by nature, but some do turn into pre-cancer or colon cancer eventually if they aren’t removed. They grow very slowly and can take as long as 20 years to form. Colon polyps can appear in a variety of shapes; this study looked at the less-common yet still risky serrated polyps.
In a randomized, controlled trial, more than 2,200 people between the ages of 45 and 75 across the country who had previously had polyps removed were studied. The researchers excluded patients who had a family history of colon cancer, inflammatory bowel disease, and other serious health problems. They also accounted for factors like weight, diet, gender, and anti-inflammatory drug use.
The patients were placed in groups that took 1,200 milligrams of calcium per day, 1,200 milligrams of calcium per day plus 1,000 IU of vitamin D3, calcium plus a placebo, vitamin D plus a placebo, or a placebo-only control group. The participants were given colonoscopies after three to five years of supplementation at the end of the treatment phase and again another three to five years later.
They found that those who took calcium on its own or in conjunction with vitamin D had a higher likelihood of polyps after six to 10 years. In addition, women and smokers had a higher risk when taking calcium but not when taking vitamin D alone. These effects were not seen in the first follow-up colonoscopies after three to five years at the end of the treatment phase, however. Their findings were published in the journal Gut.
Calcium from food doesn't have the same effect as calcium supplements
It is worth noting that the calcium supplements used in the study were calcium carbonate. It’s not clear whether this contributed to the problem, but it is known that cheap calcium carbonate, which is essentially crushed rocks, is often contaminated with lead and has been linked to kidney and artery calcification.
That’s why it is always a good idea to get calcium from high-quality supplements, or better yet, from your diet. Some foods that have a high calcium content include kale, broccoli, kefir, yogurt, sardines, cheese and bok choy. In the study, the researchers found that it was only calcium from supplements that was associated with the higher risk of polyps and not calcium obtained through food.
A similar mechanism was seen in a Johns Hopkins Medicine study looking at calcium supplements and heart disease. People who ate diets high in calcium from food reduced their risk of developing heart disease by 27 percent compared to those with a low intake of calcium, but those who took calcium supplements had a 22 percent higher risk of heart disease.
More research is needed to back up the findings of the polyp study, but those who have a history of pre-cancerous serrated colon polyps might want to avoid calcium carbonate supplements, especially women and smokers. Likewise, those who do need to supplement with calcium for whatever reason should make sure they get regular colonoscopies.
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