Calcium Supplements and Colon Polyps
Epidemiologic studies have indicated that people who have calcium rich diets are at lower risk of colon polyps, including serrated polyps. So some have reasoned that calcium supplementation might help prevent polyps. However, a University of North Carolina School of Medicine study in the journal Gut (March 2018) found taking calcium supplements daily, with or without Vitamin D supplements, might increase the risk of precancerous, serrated colon polyps. Serrated polyps are a major target of colon cancer screening as they are more difficult to detect on colonoscopy.
In the study, people taking calcium or a combination of calcium and vitamin D were more likely to develop polyps 6 to 10 years after the study began. Participants either received 1200 mg/day of elemental calcium, 1000 IU/day of vitamin D3, both or neither. Treatment was for 3 or 5 years. Calcium from dietary sources did not increase risk. The study followed 2000 people, 45 to 75 years old, all having a history of polyps. Women and smokers appeared to be at higher risk when taking calcium supplements, but not when taking vitamin D alone.
Polyps are not cancerous, but they have the potential to turn into cancer if they're not removed. No colon cancers were found in the study participants in the follow-up period.
Additional research is required to confirm the findings. I think this study may be yet another reason to focus on obtaining your calcium from food not supplements, especially for people with a history of pre-cancerous serrated polyps, women and smokers.