A study in the journal Gut found taking daily calcium supplements may increase the risk of serrated colon polyps, a precursor lesion to colon cancer. People who took calcium or calcium plus vitamin D were more likely to develop polyps from six to 10 years after the study began, but calcium from dietary sources was not associated with increased risk. The researchers added that millions of people worldwide take calcium supplements and that any possible risks have to be weighed against potential benefits.