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© ISM/SPL. Sessile serated adenoma (light micrograph).
Calcium and vitamin D supplements may increase risk of certain colorectal polyps

By Jane Lewis
In patients with a history of colorectal adenomas, calcium supplementation, with or without vitamin D, may increase the risk of sessile serrated adenomas or polyps (SSA/Ps) over time, reports a large multicentre chemoprevention study published in Gut.

Patients with a history of premalignant serrated polyps might wish to avoid calcium supplements, the authors advised.

Commenting on the findings, Professor Finlay Macrae, Head of Colorectal Medicine and Genetics at The Royal Melbourne Hospital, said the research came from a well-known interventional randomised controlled trial of supplemental calcium and vitamin D conducted by investigators who were highly regarded in the field.

‘This post-hoc analysis studied the development of a relatively new class of polyp – sessile serrated polyp – which appears to be the precursor of a less common form of colorectal cancer (CRC) that typically occurs in the right colon and is more often seen in women than men,’ he told Medicine Today.

In the US study, participants aged 45 to 75 years with one or more adenomas at baseline were randomised to receive 1200 mg/day of elemental calcium, 1000 IU/day of vitamin D, both agents or placebo. Treatment continued until scheduled surveillance colonoscopy (at three or five years; the treatment phase) with data collection continuing for a further three to five years (the observational phase) in consenting participants.

Serrated polyps were diagnosed in 565 of 2058 (27.5%) participants during the treatment phase and 329 out of 1108 (29.7%) participants during the observational phase. Although supplementation had no effect on the incidence of SSA/Ps in the treatment phase, elevated risks of SSA/Ps were seen during the observational phase (six to 10 years after supplementation began), associated with calcium alone as well as calcium plus vitamin D supplementation (adjusted risk ratios, 2.65 and 3.81, respectively). Women and current smokers were found to have higher risks of serrated polyps when exposed to supplemental calcium.

‘Further studies are recommended to confirm these results, which may have important implications for CRC screening and prevention,’ the researchers concluded.

The observed effect of calcium supplementation on risk of SSA/Ps was in contrast to its effect on conventional adenomas, with the current study finding no apparent effect and other studies finding a protective effect, the researchers noted.

According to Professor Macrae, although the effect of calcium supplementation on SSA/Ps was found in post-hoc analysis, the finding ‘mounts a strong case to study the effect of supplemental calcium on those particular polyps in more detail.’ It might also ‘send a note of caution to those taking calcium supplements,’ he added.
Gut 2018; 0: 1-12; doi: 10.1136/gutjnl-2017-315242.