Get a Dog and Start Walking

John L. Marshall, MD


March 15, 2013

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Hello, everyone. This is John Marshall for Medscape. Let me ask you a question: How much exercise did you get this week? I am in training with a team for a big, long race. We are exercising to get ready for that, so last week I ran almost 14 miles total. I was quite proud of myself. (I am hurting so much this week that I can't run at all, but that's another story.)

What do you think about running, exercise, and physical activity and your risk of developing cancer? A lot of data is emerging on this subject. Just in the last few months, 2 very interesting studies have been published on the relationship between exercise, physical activity, body mass index, and colorectal cancer. I thought it would be useful to pause and think about this a bit.

The data from the larger of these studies[1] come from Harvard's Nurses' Health Study and the Health Professionals Follow-Up Study. It includes roughly 150,000 people. Every year these participants receive a long survey asking, for example, "How much broccoli do you eat? How much exercise do you get?" In essence, the answers provide a snapshot of participants' nutrition and exercise for the whole year. Of course, we assume that these people are pretty good reporters and give us pretty good data, although if you asked me today how much exercise I get I would say a lot, whereas if you had asked me a few months ago, I might have answered differently. So, there is an innate problem with this kind of survey data but they overcome that with size. Around 150,000 people were involved in the larger study, and 2300 people were involved in the other.