New research, published in Gut, investigates the possibility that calcium supplements, taken with or without vitamin D, may increase the risk of small growths in the large bowel – called polyps.
Prof Kevin Whelan, Professor of Dietetics and Head of Department of Nutritional Sciences, King’s College London, said:
“This study is an analysis of a randomised controlled trial measuring the effects of calcium and vitamin D given either alone, or in combination, on the risk of developing polyps in the bowel. When the supplements were stopped 3-5 years later there was no effect of calcium or vitamin D supplements on the number of people developing another polyp. However, what is important about this new study is that the researchers have now undertaken a longer term analysis 6-10 years after people started. Although calcium and vitamin D had no effect on the number of people with polyps, those taking calcium supplements were over 2½ times more likely to develop a particular type of polyp that is thought to be a precursor to bowel cancer (sessile serrated polyp).
“A key strength of this study is that it investigated whether these findings could be explained by other factors not related to the supplements by taking into account age, sex, body mass index and smoking status.
“It is important to highlight that this study was performed in people who already had a history of bowel polyps and therefore we cannot assume that calcium supplements would have the same effects in healthy people who have never had polyps. More research is needed to understand the effect of calcium on the risk of polyps in the general healthy population. Calcium supplements are important for the health of our bones and studies show that those who take supplements have a reduced risk of bone fracture. Therefore, the results of this study in people already at risk of bowel polyps should not result in the public changing their intakes of calcium at this time. However, if people have a history of having polyps and are already taking calcium supplements then I recommend discussing this with your doctor or dietitian.
“The researchers also report that current smokers were more than twice as likely to develop a serrated polyp when taking calcium than non-smokers taking calcium at the 3-5 year time point, and women were over 2½ times more likely to develop serrated polyps when taking calcium than men taking calcium at the 6-10 year time point. These findings suggest that the effect of calcium on the bowel may be heightened in smokers and in women.
‘The dose of the calcium supplements given in this study (1200 mg per day) is similar to the doses used in many calcium supplements available from health food stores, pharmacies and doctors. However, it is much higher than the recommended intake of calcium from diet, which is 700 mg per day in the UK and 1000 mg per day in the US. Importantly, there was no effect of the calcium we eat in our diet on the risk of polyps, and therefore this study in no way suggests people should cut down on calcium-containing foods.”
Mr Andrew Beggs, Consultant Colorectal Surgeon and Cancer Research UK Advanced Clinician Scientist at the University of Birmingham, said:
“This is an analysis of a well-designed research study where the authors looked at patients who were taking vitamin D & calcium supplements. They found a small increase in numbers of a type of pre-cancerous polyp in the bowel of patients who took calcium supplements. This study has major limitations as the number of patients they identified with this rare type of bowel polyp was small. Therefore we cannot be sure that there is a link between taking calcium and Vitamin D supplements and bowel polyps. Patients should continue to take these supplements if advised by their doctor as the benefits far outweigh the small risk identified in this paper.”
‘Calcium and vitamin D supplementation and increased risk of serrated polyps: results from a randomised clinical trial’ published in Gut on Thursday 1st March 2018.