Contrary to previous research vitamin D and calcium supplements do not lower the risk of colorectal adenomas, a randomised trial published in the NEJM finds.

The study randomised 2259 patients with recently diagnosed adenomas that were removed following colonoscopy to supplementation with 1000 IU of vitamin D3, 1200 mg of calcium.

Both supplements did not significantly affect the risk of colorectal adenomas over a three to five year period, the study authors found.

Although the findings for vitamin D were inconsistent and demonstrated “modest chemopreventive potential” they did not support the more marked chemopreventive effect that has sometimes been posited, they said.

However, the researchers said given the strong data supporting a chemo-preventive effect of calcium supplementation (including findings in their own previous trial) they were surprised to find it had no effect.

A high prevalence of obesity in their study population could explain the lack of a calcium effect requires and required further investigation, they said.