Paul Williams is a scientist at Lawrence Berkeley (Calif.) National Laboratory who runs the world's largest study of runners' health, known as the National Runners' Health Study. He has more than 100,000 participants, some of whom he's been following more than 20 years.
This year, several reports have come out suggesting that more is not better when it comes to how much running people should do to improve their health. But in his research, Williams has yet to find an upper limit to safe running distances — in fact, his runners continue to see increased health benefits all the way up to 100 miles a week of training. Williams himself runs about 35 miles a week.
Q: Let's cut to the chase: Is endurance running good or bad for us?
A: Certainly there is evidence that it's good for us. People who are running more marathons and faster marathons are at lower risk for hypertension and other things. In my survey, I haven't seen anything to suggest they would be at a disadvantage.
Q: So why does this impression that long-distance running is harmful persist?
A: Well, there are these people who do die during the marathon. I think some of the attention to this issue is from the irony. People who haven't run a marathon or don't run at all, they can say, "You see, I should be watching television, not out there killing myself."
But it's still worthy to be looking at these things scientifically, to better understand what's going on. ... Maybe we can figure out who might be at more risk or less risk.
Q: A few studies have come out recently that suggest there's a "U-shaped curve" to the benefits of endurance exercise — in other words, that at some point the benefits level off, and eventually people can do more harm than good with excessive exercise. What does your research of runners show?
A: It's important to not rush to any conclusions that 10 to 20 miles a week is the optimal dose. I haven't seen anything to suggest a U-shaped relationship.
Things might start to plateau about 50 miles a week, but even among my runners there are very few people running 50 miles a week anyway. At some point you figure it's going to level off.
Q: What are some of the benefits from distance running that you've seen in your research?
A: One of the things that pleases me is how broad-spectrum the results are. Nobody in our cohort really gets sick at all until they're about 60. There's this huge spectrum of benefits, and some of them are not the subtle things like lower cholesterol and blood pressure, but things like feeling better and body weight, and being fitter.
Here's one simple thing: There's about a 30 percent reduction in the risk of cataracts. That's something that is a major medical expense, and just improving that could have extreme public health advantages.
The thing that people need to get about exercise is, it's not to correct a condition you have, it's to prevent getting sick in the first place.
Q: What more needs to be studied in this field?
A: We want to study them longer. Very few people have problems before 60. The youngest in my study was 18 when it started, and I've got some people who are in their late 90s who haven't died yet.
We started in 1991 and these things get to be more and more interesting as you go on. There are other things we want to look at, such as Parkinson's disease and cancers.
Q: Assuming most people aren't running purely for the health benefits, what do you think is the appeal of distance running?
A: Part of it is personal appearance. I think part of it is getting out, having a break during the day.
Running is something most people can step out their door and just do. In general, it's something that's achievable. And certainly when people get to be more extreme runners, they start getting this endorphin high and positive feedback and they just feel better.