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*Text Courtesy Reuters

(Reuters) - Fit 50-year-olds are less likely to get chronic diseases as they age than are couch potatoes, according to a new U.S. study.

It may seem like a no-brainer, but the study helps fine-tune our understanding of the link between fitness and healthy aging, researchers say.

"It has been known for decades that if you are more fit, you live longer," Dr. Jarett Berry at the University of Texas Southwestern Medical Center, Dallas, told Reuters Health. "But it has not been clear that you have a higher quality of life, that you age better."

It's possible that fit people just delay the onset of chronic illness, for instance, and end up being sick just as long as their weaker peers. But that doesn't appear to be the case, according to the new research, published in the Archives of Internal Medicine.

"We see truly reduced chronic disease, rather than just delaying the inevitable," said Berry, who led the work.

He and his colleagues studied more than 18,600 healthy men and women, who had done a treadmill test sometime around age 50 to measure their cardiorespiratory fitness.

Using Medicare claims data spanning an average of 26 years, the researchers then linked the treadmill results to the rate of eight chronic conditions, including heart disease, diabetes, Alzheimer's disease and colon cancer.

Among men in the lowest fifth of fitness scores, the rate of chronic disease was 28 percent per year. By contrast, the rate was only 16 percent per year among the top fifth.

For women, the numbers were 20 percent per year versus 11 percent, respectively.

The findings don't prove that exercising more cuts the risk of chronic disease, because it could be that people with a lot of physical activity also eat healthier foods - something the researchers didn't take into account (they did account for smoking, alcohol use, obesity, blood pressure and cholesterol levels).

In a commentary, Dr. Diane Bild of the National Heart, Lung and Blood Institute in Bethesda notes that there could also be genetic factors that predispose people to both fitness and health.

But she adds that, "Physical activity has a host of well-proven benefits, including effects on weight, cardiovascular disease risk factors, bone health and mental health."

Berry said even if genetics are at work, it doesn't mean exercise can't make a difference. He said national guidelines recommend 150 minutes of moderate-intensity exercise or 75 minutes of high-intensity exercise every week.

The new study would seem to argue for more-vigorous activities such as jogging, cycling or playing basketball, he said.

"We know from prior literature that higher-intensity exercise tends to translate into more fitness," Berry explained. "Walking is clearly better than doing nothing, but if you can make the choice between walking and jogging, then jogging is probably better for you."

SOURCE: bit.ly/Ny7r8O and bit.ly/RSNO2Q Archives of Internal Medicine, online August 27, 2012.