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Health Sense

High water marks

There’s no question swimming is good for you. Is it better than running or walking? Not so fast.

By Judy Foreman
Globe Correspondent / June 14, 2010

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Is swimming the best exercise for lifelong health?

After all, you can swim with just your arms if you have a bum knee, or with just your legs if you have sore arms. You can swim with arthritis. Or a recently replaced hip.

An article in the May-June 2010 issue of SWIMMER floats the notion that swimming just might be a life preserver. The report is based on the first major study comparing the long-term benefits of swimming with other activities, which concluded that “swimmers had lower mortality rates than those who were sedentary, walkers or runners.’’

The research was conducted by Steven Blair, a leading exercise scientist from the University of South Carolina, and funded by the National Institutes of Health and the National Swimming Pool Foundation. It appeared in the International Journal of Aquatic Research and Education, a peer-reviewed journal published by Human Kinetics and the foundation. The 2008 study followed 40,547 men ages 20-90 who completed health exams between 1971 and 2003.

But is swimming really better for you? And if so, why?

Blair himself, in a telephone interview, is cautious. The 13-year study, he says, does “show that swimmers have lower death rates’’ than sedentary people, walkers, and runners. “That’s what the data show.’’ But are swimmers more fit than runners? “It doesn’t quite make sense to me,’’ he says and laughs.

Over the course of the research, 1,336 of the 20,356 runners (or 6.6 percent) had died, compared with only 11 of the 562 swimmers (1.9 percent). But the number of swimmers was so small that if a few more had died, it could have significantly changed the conclusions, he says.

In addition, the study was “observational,’’ that is, the researchers simply followed the different groups of people over time to see how they fared, as opposed to randomly assigning them to different types of exercise — a more rigorous way to conduct research.

“My guess is that there were a lot of differences between people who chose to be swimmers instead of runners or walkers. Swimmers may have been healthier to begin with so their lower death rate may have had nothing to do with swimming,’’ says Dr. Steven Woloshin, a professor of medicine at the Dartmouth Institute who analyzes the interpretation of scientific studies.

The study had other limitations: Only men were studied. It also didn’t track whether participants continued with the exercise they were doing at the start of the study period. And while the study did classify the runners and walkers by pace, it didn’t specify swim ming paces at all — no differentiation was made between the swimmers who dogpaddle a bit and never get their hair wet, and those who are dynamos in the water.

Still, after the authors adjusted their findings for differences in age, weight, smoking status, and other risk factors, the swimmers had lower all-cause mortality than the men who were sedentary, walkers, or runners.

In another 2008 study led by Blair, of men and women subjects using treadmill tests and other measures of cardiorespiratory fitness, runners scored the best, with swimmers a close second.

On the downside for swimming, one of its chief benefits — being weightless in the water, a boon for aching joints — can also be a disadvantage.

“Swimming does not build bone’’ like running does, says Dr. Michael Holick, an osteoporosis expert at the Boston University School of Medicine. “It’s pounding the pavement that is translated to hip and spine bone strength. Even treadmills and elliptical machines are not the same.’’

On the other hand, he says, “there’s no evidence that swimming makes [bone loss] worse.’’ And swimmers do develop good muscles, and muscle mass “usually equates with higher bone density.’’

The most important message of all the research is that physical activity of any sort is crucial for good health and longer life.

“There are so many things people can do for physical activity,’’ says I-Min Lee, an epidemiologist at Harvard Medical School who studies physical activity and health. “You can pick what you like. We’re not forcing everybody to run or play tennis.’’

Blair’s findings about the benefits of swimming are “encouraging, though by no means definite,’’ Lee says.

Peter Katzmarzyk, a professor of epidemiology at the Pennington Biomedical Research Center in Baton Rouge, La., who also studies exercise and health, agrees. “I can’t say everybody should be swimming as opposed to other things,’’ he says. But at the very least, the study shows that swimming “accrues the same benefits as other activities, and that was never shown before.’’

A sedentary lifestyle is a major risk factor for premature mortality from all causes. It’s also a risk for many chronic diseases, including Type 2 diabetes, cardiovascular disease, and cancer.

Put the other way around, people who expend more than 1,000 calories a week in exercise cut their risk of dying — from all causes — by 20 to 30 percent, and those who do more cut their risk even more. Physically active people have lower (healthier) fasting blood glucose levels and insulin resistance, and are better able to control their weight. They also have lower blood pressure, total cholesterol, and “bad’’ low-density cholesterol.

As for swimming as an exercise choice, more research is needed. But the data so far suggest that it’s right up there with running as a great way to get and stay fit. And it’s certainly easier on the knees, a huge advantage for many people as they age.

Besides, there really is something about sliding into the water, outdoors or in a pool, and moving quietly along. After all, life evolved in the water. Why not head back in?

Send comments to gsection@globe.com.

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