Colorectal cancer patients with high levels of vitamin D in their blood are more likely to survive the disease, a study shows. Patients with the highest levels of vitamin D have half the risk of dying compared with those with the lowest levels.

The study is the first to correlate total blood levels of vitamin D in colorectal cancer patients after their diagnosis, which includes that produced after exposure to sunlight and that obtained from dietary sources, with their long term survival prospects. The study was published in the Journal of Clinical Oncology (2014; doi:10.1200/JCO.2013.54.5947).

The team, from the University of Edinburgh in the United Kingdom, tested blood samples from almost 1,600 patients after surgery for colorectal cancer. The greatest benefit of vitamin D was seen in patients with stage II disease, at which the tumor may be quite large but the cancer has not yet spread.

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Researchers found that three quarters of the patients with the highest vitamin D levels were still alive at the end of 5 years, compared with less than two-thirds of those with the lowest levels.

The results show that vitamin D is associated with a much better chance of cancer survival, although the nature of this relationship is not clear from this study.

The study’s authors aim to set up a clinical trial to test whether taking vitamin D tablets in combination with chemotherapy can improve colorectal cancer survival rates. Measuring vitamin D levels in colorectal cancer patients could also provide a useful indication of prognosis, the scientists said.

“Our findings are promising but it is important to note that this is an observational study. We need carefully designed randomized clinical trials before we can confirm whether taking vitamin D supplements offers any survival benefit for bowel cancer patients,” said Professor Malcolm Dunlop, MD, of the Medical Research Council Human Genetics Unit at the University of Edinburgh.