Blood pressure drugs don’t protect against colorectal cancer
A new study has found that, contrary to current thinking, taking beta blockers that treat high blood pressure does not decrease a person’s risk of developing colorectal cancer. Published early online in CANCER, a peer-reviewed journal of the American Cancer Society, the study also revealed that even long-term use or subtypes of beta blockers showed no reduction of colorectal cancer risk.
In recent years, researchers have thought that beta blockers, which are prescribed to many older adults for high blood pressure and heart conditions, might be linked with a decreased risk of cancer. This theory stems from animal and laboratory studies that found that the stress hormone norepinephrine can promote the growth and spread of cancer cells. Beta blockers inhibit norepinephrine’s action, so it stands to reason that the medications could have anticancer properties.
Previous studies on beta blockers’ effects on colorectal cancer risk have yielded inconsistent results. To provide more thorough information, Michael Hoffmeister, PhD, of the German Cancer Research Center, in Heidelberg, Germany, and his colleagues conducted personal interviews from 2003 to 2007 with 1,762 patients with colorectal cancer and 1,708 cancer-free individuals.
After taking into consideration certain patient characteristics (such as weight and smoking status) and other factors that might influence the results, the researchers found no link between beta blocker use and colorectal cancer risk. Previous studies had not taken these factors into consideration. Even when the investigators broke down their analyses by duration of use of beta blockers, specific types of beta blockers, active ingredients (metoprolol, bisoprolol, carvedilol, and atenolol), and sites within the colon or rectum where colorectal cancer developed, there was no link.
Overall, the results of this study do not support the hypothesis that using beta blockers can lower one’s colorectal cancer risk. The findings also point to the importance of considering patient characteristics and other factors that might influence the results of studies that look at how medications affect patients’ cancer risk.
PROTECTING YOURSELF AGAINST COLON CANCER
Of all the cancers, colorectal is the one where the role of diet as a cause of the disease has been the most intensively studied. As a result, there has been a plethora of research studies on all aspects of diet. Although not all the findings agree, there’s enough evidence to formulate broad dietary strategies that will minimise your risks of developing the disease.
Eat at least 30 g of fibre a day. That was the recommendation of a recent colloquium of experts (American Health Foundation, New York, April 1998). Although the American Health Foundation recommended that most fibre come from wheat, wheat has been found to present many other problems and might well be substituted with a gluten free grain such as rice, millet or buckwheat, or ancient wheat precursors such as kamut or quinoa.One study showed that a daily intake of less than 7.5 g doubles the risk of colon cancer (Int J Cancer, 1989; 44: 1-6).
The generally accepted theory has been that a high fibre diet increases the bulk of the faeces, accelerating their “transit time” in the gut, and so reducing the exposure of the colon wall to possible carcinogens. But high fibre foods also seem to actually limit the number of carcinogens present. Experiments on human volunteers, comparing oats, wheat bran and cellulose, showed a considerable reduction in carcinogens present in the faeces with wheat and cellulose, but not with oats (Cancer Research, 1989; 49: 4629-35). Further animal tests showed that all the chemical constituents of the whole wheat germ had a protective effect against polyps and tumours, but that the largest effect came from the crude fibre itself (Mutat Res, 1996; 350: 185-97).
Such findings have been confirmed in epidemiological studies which show that diets high in cereal fibre reduce the risk of colon cancer, while refined grains increase it (Cancer Causes Control, 1997; 8: 575-90).
Increase your consumption of vegetables to at least five portions a day. Higher intakes of vegetables, but not fruit, also seem to have a protective effect, according to a long term study using data from the Food and Agriculture Organisation, where both cereals and vegetables were found to protect against colon cancer, particularly in later life (Eur J Cancer Prev, 1998; 7: S11-S7).
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Exercise and colorectal cancer
People who exercise more have a lower risk of bowel cancer. One study pooled the results of over 50 other research projects and included over 100,000 cases of bowel cancer in total. It provides the strongest evidence yet of the role of exercise, with the risk of bowel cancer being 50% lower in people who exercised regularly – half the risk. This lower risk remained even when other factors such as diet, smoking and obesity were taken into account.
The other good news is that any decent exercise will do. The studies included manual work, hiking and gardening as well as sports. We don’t know why exercise helps. It may affect your hormone levels. Or it may change the speed at which your body ticks over (your metabolic rate). Or it may even change the time your food stays in the bowel.
Amy Molnar
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Wiley-Blackwell