Thursday, February 26, 2009

Globe Story on Cancer Prevention

Some project that cancer will soon overtake heart disease as the world's leading cause of death. Today's Globe has this interesting story about a report from experts in nutrition epidemiology on the benefits of cancer prevention. The report concludes that 25% of cancers could be prevented with appropriate nutrition and physical exercise.

This report is of particular interest to me for many reasons. Firstly, as a society we should take prevention much more seriously than we do. We must encourage everyone (young and old alike) to eat a healthy diet and exercise. I have noted this many times before (here, here and here).

Secondly, this story interests me given my interest in genetic justice. This paper, for example, examines the diverse considerations that arise-- given genetic complexity-- when we think about how best to mitigate our vulnerability to diseases like cancer.

Thirdly, this story and study reveal how complex and difficult it is to appreciate what a 25% prevention of cancers actually means. It does not mean that active people will not get cancer. For most people it means they will be able to delay the time it takes them to develop a different form of cancer that is not preventable by life style, or another disease of aging. Furthermore, eliminating all cancer would not (contrary to what most people think) dramatically increase life expectancy for humans. These points are worth emphasising for they reveal the importance of aging research.

Take smokers. Smoking increases one's risk of lung cancer. There are both genetic (see this) and environmental (tobacco contains hundreds of carcinogens) reasons for this. All else being equal, smoking lowers one's life expectancy when compared to non-smokers. But never smoking doesn't mean you won't get cancer (even lung cancer). There are still another 200+ kinds of cancer that we could develop and die from.

Furthermore, people often overestimate what eliminating all cancers would mean for the life expectancy of humans. We tend to think that eliminating cancer would add decades to a person's life expectancy. But this is not the case. It would add about 3 years to life expectancy at birth. Why is the increase so small? Because of the fact of co-morbidity. If you don't die from cancer chances are you will soon die of heart disease, stroke, or one of the other afflictions associated with senescence.

Now of course exercise and proper diet can reduce your risk of these other afflictions as well. I in no way mean to trivialize these benefits or undermine the importance of lifestyle. But at the same time it is important not to hype what these benefits will be. You often hear people say that anyone could live to a 100 years with proper diet and lifestyle. But this is false. There is no credible scientific basis for believing that lifestyle changes would increase the maximal human life span (which is around age 85).

Exercise is not as effective as calorie restriction in terms of extending lifespan. Just to be clear, I am not suggesting that we pursue CR. Rather my point is that we should support the science that could develop a safe and effective pill that would mimic the effects of CR, thus reducing our risks of disease and death in later life.

So decelerating aging is the most important form of prevention for aging populations. I'm a fan of all forms of prevention. The greater their proposed benefits (in terms of quality of life) and the more likely it is that people will utilize them, the more important they are. A pill the slows aging is something everyone could take (unlike regular exercise and nutrition) and it would add significantly more health to our life prospects than exercise and diet alone. So if you are excited about the prospect of reducing your risk of 25% of cancers by exercise and diet, you should be "over the moon!" about the prospect of reducing your risk for cancer, heart disease, stroke, etc... etc... by decelerating aging.