Cancer prevention by Andrea Eisen, MD, FRCP(C), Verna Mai, MD, MHSc, FRCP, Julia Knight, PhD

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Whether it's the Brussels sprouts to prevent bladder cancer or blueberry punch against prostate cancer -- there s no shortage of publicized advice on how to thwart malignant growths. Experience shows that few of these propped up "miracle workers" are likely to stand the test of time, yet the prospect of holding cancer at bay remains tantalizing. we've summoned a panel of experts to discuss what s known and established in this regard, and to provide some insights into what the future may hold.

PE: How much can cancer be prevented?
Dr. Mai: There are estimates that one-third to one-half of all cancers can be prevented. To achieve this goal, you d have to eliminate smoking exposure and people would need to eat properly. This includes the recommended 5-10 servings of fruits and vegetables a day, low red meat intake and minimal alcohol consumption -- all those things may help reduce a person s risk of getting cancer. The trick is to actually get all these measures adopted across the population.

Dr. Knight: I think the feeling is that cancer, to a fairly large degree, should be preventable, partly because we know of differences in disease incidence between countries and that the rates change when people move from one place to another. This implies that there are things about our lifestyle and environment that can be altered and influence our risk. Although genetics certainly play a role, we know that the non-genetic factors are also very important.

PE: What are some of the non-genetic risk factors?
Dr. Eisen: The most obvious one is tobacco. Its use is thought to account for about 30% of all deaths from cancer worldwide. Then, if you lump together diet, obesity and physical inactivity, they explain another 30%, and a really strong family history probably accounts for 5-10% of cases. There s also alcohol, which is being increasingly recognized as a risk factor for the more common cancers -- it's probably implicated in a little less than 5%. Occupational and environmental exposure is responsible for 5-10% of cancer deaths.

Dr. Knight: My primary area of expertise is breast cancer, which is tricky because some of the things that we know increase the risk of breast cancer are hormone-related. So we've tried to look at other things that we may be able to modify more easily. For example, it's pretty clear when you look at all the evidence, that alcohol increases the risk of breast cancer. it's also been consistently shown that physical activity can reduce the risk, but there are still things we don t know, such as: how physically active does a person have to be? What type of exercise? When in the lifetime? And, how does it affect the risk? We still need more evidence, but what we know now suggests that vitamin D can help reduce the risk of breast cancer, and possibly other tumours as well. If a woman makes sure she gets her vitamin D, reduces her alcohol consumption and keeps physically active, all these things combined could start to have quite a significant preventive effect.

PE: Do any specific lifestyle changes reduce the risk of cancer?
Dr. Eisen: The American Institute for Cancer Research (AICR) published a report recently that made 8 recommendations, which are a little more specific than usual. For example, the researchers advocate being as lean as possible without being underweight -- so our body mass index criteria may be too generous on the upper end. The report also advises people to be physically active for at least 30 minutes a day, to eat a variety of vegetables, fruits, whole grains and legumes, to limit consumption of red meat and, in particular, to avoid processed meat. As well, people should stay away from salty foods and items processed with salt. Men shouldn t drink more than two drinks of alcohol per day while women only get away with one drink daily.

Dr. Knight: One very interesting thing that came out of the AICR report is the recommendation that it's better to get nutrients from food rather than supplements. Some of the prevention trials investigating supplements have been disappointing, and I think the feeling now is that the preventive effects of a good diet aren t just related to individual nutrients. it's something more complex than that, such as overall dietary patterns.