The findings are based on the European Prospective Investigation into Cancer study (EPIC) of 520,000 people living in western Europe.
Participants filled out detailed dietary and lifestyle questionnaires and circulating vitamin D levels were measured over several years.
During the study period 1,248 people developed colorectal cancer. When researchers matched these cases to an equal number of healthy controls, they found that participants with the highest levels of circulating vitamin D were 40% less likely to develop colorectal cancer than those with the lowest levels.
While these are significant findings, the authors have urged caution over the use of vitamin D supplements to prevent colorectal cancer, pointing out that very little is known about the long term effects of high vitamin D levels.
They concluded: ‘Before any public health recommendations can be made for vitamin D supplementation, new randomised trials are needed to test the hypothesis that increases in circulating vitamin D concentration are effective in reducing colorectal cancer without inducing serious adverse effects.'
In the meantime, people can reduce their risk of developing colorectal cancer by stopping smoking, maintaining a healthy weight and cutting down on alcohol and red meat intake, the researchers said.