You eat calcium-rich foods such as yogurt and dark  leafy greens, but to really ensure bone health, you take a calcium supplement every day.

Perfect, right? Not so fast. A study done at the University of North Carolina School of Medicine revealed a surprising and dangerous consequence of taking calcium supplements—an increased risk for serrated polyps in the colon, a type that can develop into colon cancer.

The study: Researchers studied more than 2,000 people between the ages of 45 and 75 who had had a colonoscopy that uncovered at least one polyp and who were scheduled for a follow-up cancer screening in three to five years. They found that participants with a history of precancerous polyps who took supplements of 1,200 mg of calcium (with or without vitamin D) had an increased risk of developing more polyps within six to 10 years of starting the supplements. Within this group, women and smokers were the most at risk.

The results were surprising to even the researchers because earlier studies found that patients with higher calcium intakes had a decreased risk of developing colon polyps and cancer. However, many of these studies looked at calcium in the diet versus the supplemental calcium studied in this trial.

What this means for you: While more research is needed, this was a high-quality study, and it inevitably leads to the question, Should some people stop taking calcium supplements because of the possible increased risk for precancerous colon polyps? According to the lead author of the study, Seth D. Crockett, MD, MPH, the answer is yes for the following people—those who smoke…who have a history of precancerous polyps…or who take supplements not because they were told they need to increase bone density but for dubious reasons such as the chewy chocolate ones taste good. For these groups of people, it’s reasonable for now to act as if the benefits of calcium supplements would not outweigh the risks.

If you don’t have a history of polyps and don’t smoke, you should be able to safely take calcium in a lower dose than was used in the study, Dr. Crockett said. Multivitamins, for instance, typically contain a 200 mg of calcium, about one-fifth of the recommended 1,000 mg suggested daily RDA for women under age 50 and men under age 70 and one-sixth of the 1,200 mg suggested for over ages 50 and 70, respectively.  How to make up the difference? It’s always best to get your daily calcium from food.

In addition to dairy, foods rich in calcium include  white beans, Chinese cabbage, dried figs, oranges, kale and broccoli. It’s better to spread your calcium intake out over the day for maximum absorption—no more than 500 mg at a time, so avoid having yogurt and cheese at the same meal, for instance. Also, don’t forget potassium.

Dr. Crockett also stressed the importance of getting colonoscopies as often as recommended for you, based on your age and family and personal medical histories. This may not be a test you look forward to, for sure—but it’s critically important for preventing colon cancer and cancer deaths, he added.

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