Study finds people with highest vitamin D blood levels have 40% lower risk of colon cancer than those with lowest

Adapted from a press release issued by the British Medical Journal

People with high levels of vitamin D in their blood have a lower risk of colon cancer than those with low levels, according to a large European study published today in the British Medical Journal.

It is estimated that around three in every hundred people in Europe will develop colorectal cancer during their lifetime.

Today’s research found that people with the highest blood levels of vitamin D had a 40% lower risk of colon cancer than those with the lowest. No such association was observed for rectal cancer in the study, which was led by teams from Imperial College London and the International Agency for Research on Cancer.

Previous laboratory work had suggested that vitamin D may help prevent the growth of colon tumours. However, earlier epidemiological studies, which mainly used dietary questionnaires to compare how much vitamin D people were obtaining, had proved inconclusive.

The new findings are based on the European Prospective Investigation into Cancer study (EPIC) of over half a million people from 10 Western European countries, which is led by Imperial’s Professor Elio Riboli. Between 1992 and 1998, participants completed detailed dietary and lifestyle questionnaires and provided blood samples.

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They were then tracked for several years, during which time 1,248 cases of colorectal cancer were diagnosed and these were matched to 1,248 healthy controls. Colorectal cancer is the combination of colon and rectal cancer cases.

The results showed that high levels of vitamin D in the blood were linked to a lower risk of colon cancer.

Professor Riboli, the Head of the School of Public Health at Imperial, said: “This was a large and very carefully designed study and it gives strong evidence that vitamin D plays a role in protecting against colon cancer. Based on this study and previous research, we know that if you want to reduce your risk of developing colorectal and other cancers you should stop smoking, increase your physical activity, reduce obesity and abdominal fatness, and limit your intakes of alcohol and red and processed meats. We also know that making sure you get some exposure to sunlight, without harming your skin, is important for keeping your levels of vitamin D up.”

The researchers did not find a link between the risk of colon cancer and intake of vitamin D in the diet. They suggest that this may mean that exposure to sunlight is more important than diet for increasing blood levels of vitamin D, or that the dietary questionnaires did not provide a sufficiently detailed picture of vitamin D intake.

The researchers stress that their study does not provide evidence that taking vitamin D supplements, or eating foods fortified with vitamin D, can protect against colon cancer.

They say that little is known about the association between vitamin D and other cancers and about the long term health effects of very high circulating concentrations of vitamin D. It is still unclear whether taking vitamin D supplements provides any better protection against colon cancer than eating a balanced diet and having regular and moderate exposure to outdoor sunlight.

“What we can’t say yet is whether taking additional measures to increase your vitamin D levels, such as taking vitamin supplements, would have any effect on reducing your risk of developing colon cancer. There needs to be further research to establish whether or not vitamin supplements have any benefit and what side effects these might have. I would caution people against trying to increase their vitamin levels through supplements until this kind of research has been carried out,” added Professor Riboli.

Professor Riboli discusses the study in more detail in the video above.

The study was funded by the World Cancer Research Fund.

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