Press releases

Study links higher levels of Vitamin D to lower bowel cancer risk

22 January 2010

People who have higher levels of vitamin D in their blood are significantly less likely to develop bowel cancer, according to a study published today (January 22) in the British Medical Journal.

The study, the largest ever of the subject, looked at Vitamin D levels in 1,248 people with bowel cancer and found that those with the highest levels were at 40 per cent lower risk compared to those with the lowest levels.

The research was carried out by scientists at the International Agency for Research on Cancer (IARC) in Lyon, France, and Imperial College London, and was funded by World Cancer Research Fund (WCRF).

The researchers have said that while the study is interesting and supports the findings of other smaller studies, these findings do not mean people should take Vitamin D supplements to reduce their bowel cancer risk. This is because very little is known about the association of vitamin D with increased or decreased risk of other cancers. In addition, the health effects of long term (over a year) exposure to high blood levels of vitamin D are currently largely unknown.

WCRF recommends not taking vitamin supplements to prevent cancer and instead suggests people aim to meet their nutritional needs through diet and lifestyle changes. This is because it is difficult to make confident predictions on what impact supplements – and particularly high-dose ones – may have on cancer risk. In the case of Vitamin D, a balanced diet and short periods of exposure to sunlight (about five to 10 minutes) should be sufficient to maintain good levels.

According to the latest study, people with the lowest levels of vitamin D in their blood were more likely to develop bowel cancer than people with medium levels. But people with the highest levels did not have a significant further decrease to their risk compared to those with medium levels.

Dr Panagiota Mitrou, Science Programme Manager for WCRF, said: “This is the biggest ever study on this subject and there is now quite a lot of evidence from studying populations that people who have low levels of vitamin D are more likely to develop bowel cancer. The next step is to carry out new clinical trials to try to confirm whether vitamin D supplementation can reduce the risk of bowel cancer and whether there are any harmful effects of higher levels of vitamin D.

“Looking at the figures in this latest study, it suggests that increasing the UK’s vitamin D intake by 10 per cent could prevent seven per cent of cases. And when you think that there are about 37,500 cases diagnosed in the UK every year that could have a big impact.

“But we need to emphasise that, for the moment, the findings need to be treated with caution and they are certainly not enough evidence to suggest that we should be taking supplements to increase levels of vitamin D. In fact, we recommend that, generally speaking, people do not take supplements for cancer prevention.

“There are, though, some situations where supplements are recommended. For example, it is a good idea for pregnant women and nursing mothers to take a vitamin D supplement.

“The best advice for reducing risk of bowel cancer remains to stop smoking, maintain a healthy weight, be regularly physically active, to eat more fibre and less red and processed meats and to cut down on alcohol. In fact, scientists estimate 43 per cent of bowel cancer cases in the UK could be prevented in this way.

“When you consider that smoking is also a risk factor, it is clear that there is already a lot people can do to reduce their risk of bowel cancer.”

Dr Mazda Jenab, the lead author of the study from the International Agency for Research on Cancer, said: “our results support a role for vitamin D in the etiology of colorectal cancer, but this has to be balanced with caution regarding the potential toxic effects of too much vitamin D and the fact that very little is known about the association of vitamin D with either increased or reduced risk of other cancers”.

Professor Elio Riboli, the lead researcher, said: “There is consistent scientific evidence that low circulating vitamin D levels is a marker of increased risk for developing bowel cancer.

“However, any public health advocacy of inducing higher circulating vitamin D levels by supplementation, as opposed to the average levels that can be achieved with a balanced diet combined with regular and moderate exposure to outdoor sunlight, should await clear cut results from double blind randomized trials that are designed to test the hypothesis that increases in circulating vitamin D concentration via supplementation are effective in reducing colorectal cancer risk without inducing serious adverse events”.

Because the findings of previous randomised trials have been inconsistent, the researchers have emphasised that more research on this is needed.

ENDS

Notes to editors:

• Some recent publications have suggested maintenance of blood vitamin D levels at 50nmol/l or higher for colorectal cancer prevention. Because of this, the authors of this study also compared low and high levels of blood vitamin D concentration to a mid-level of 50-75 nmol/l. This comparison showed that while levels below the mid-level were associated with increased risk, those >75 nmol/l were not associated with any additional reduction in colon cancer risk compared to the mid-level.
• The term “bowel cancer” refers to colon cancer and cancer of the rectum. In this study, an increase risk was observed for colon cancer but not for cancer of the rectum. The increase in risk of cancer was for both men and women.
• Strength of the study are its large size, the fact that it looked at data collected before participants were diagnosed with cancer and that it took other risk factors for bowel cancer such as obesity and alcohol consumption into account. The study utilized a biomarker of vitamin D, accounting for vitamin D obtained from the diet, from supplements and from sun exposure.
• Foods that are high in vitamin D include things like dairy products, fortified breakfast cereals and oily fish.
• Dr Mazda Jenab (IARC), Prof Elio Riboli (Imperial) and colleagues used the European Prospective Investigation into Cancer and Nutrition (EPIC), which has diet and lifestyle data for more than 500,000 Western Europeans.
• The study is the largest ever conducted on the topic and is one of the first on European populations. The results confirm previous findings from smaller studies, which were based mostly on people in North America.
• Globally, more than 1 million cases of bowel cancer are diagnosed every year. About 37,000 cases are diagnosed a year in the UK.
• Some groups of people may benefit from taking supplements. These are the most common situations when taking a supplement would be beneficial: All women intending to conceive a child should take a 400mcg folic acid supplement before conception and up to the 12th week of pregnancy; Pregnant women and nursing mothers should take a vitamin D supplement and possibly an iron supplement if their iron level is low; Children between six months and five years could benefit from taking drops containing vitamins A, C and D; Children with a good appetite who eat a wide variety of foods may not need them; Frail older people who have low calorie needs may benefit from a low-dose multivitamin supplement. Older people should consider taking a vitamin D supplement, as should: people of Asian origin; people who rarely go outdoors; those who don’t eat meat or oily fish.

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About WCRF

World Cancer Research Fund (WCRF) raises awareness that cancer is largely preventable and helps people make choices to reduce their chances of developing the disease.

This includes research into how cancer risk is related to diet, physical activity, and weight management, and education programmes that highlight the fact that about a third of cancers could be prevented through changes to lifestyle. For more information on the charity’s work, visit www.wcrf-uk.org

The WCRF report, called Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective, was launched in November 2007 and is the most comprehensive report ever published on the link between cancer and lifestyle. For more information, visit www.dietandcancerreport.org