The Centers for Disease Control and Prevention study, based on a telephone survey from 2010, found that 62 percent of adults walk 10 minutes or more a week, up from 55.7 percent in 2005.

However, only 48 percent of adults exercise enough to improve their health, which was up from 42.1 percent in 2005, the CDC said.

The agency recommends at least 150 minutes per week of aerobic exercise, such as brisk walking, which can lower the risk of heart disease, stroke, type 2 diabetes, depression and some forms of cancer.

"Physical activity is the wonder drug," CDC director Dr. Thomas R. Frieden told reporters. "It makes you healthier and happier. More Americans are making a great first step in getting more physical activity."

According to the CDC study, which analyzed survey responses from 23,129 adults, 15 million more Americans are walking at least 10 minutes per week than was indicated in the 2005 study.

Despite the increase in walkers, the average amount of time adults spent walking dropped from 15 minutes a day in 2005 to 13 minutes in 2010, the CDC said.

The West had the highest percentage of walkers, with 67.5 percent saying they walked at least 10 minutes a week, compared to 56.8 percent in the South which had the lowest percentage nationally.

However, the South had the most improvement in the nation over 2005, Frieden said.

"People in the South who have traditionally had higher rates of obesity and higher rates of heart disease and stroke actually had the highest percentage increase in proportion of people who walk, up 8 percentage points," the CDC director said.

Walking is attractive for exercise because it requires no special skills or equipment and can be done alone or in groups, indoors or outdoors, the CDC said.

It recommends adding more walking trails and street lights to encourage walking, along with speed bumps and other techniques to slow traffic. The CDC also encourages agreements between local governments and schools to allow community members to use tracks after school hours.

Employers should also encourage workers to walk during breaks, Frieden said.

(Editing By Tom Brown and Eric Walsh)

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