London: Americans living at higher altitudes were more likely to be slimmer than those in low-lying areas, says a new research.

Jameson Voss, from Uniformed Services University in Maryland, who led the research, said: "I was surprised by the magnitude of the effect...I wasn't expecting such a consistent pattern as what was emerging."

The study was based on data from 400,000 people living in Colorado. The figures showed a person's obesity risk dropped with every 660 feet increase in elevation.

"It provides some evidence that these associations persist over the long term," Voss said.

Cynthia Beall, who researches how the body adapts to high altitudes but was not involved with the new study, said it's common for travelers to high elevations to burn more calories in their first few weeks, the International Journal of Obesity reports.

Researchers combined information from several databases, including a telephone health survey of 422,603 Americans from 2011. They had information on 236 people who lived at the highest altitude of at least 9,800 feet above sea level. Those people tended to smoke less, eat healthier and exercise more, according to the Daily Mail.

The researchers also had information on 322,681 people who lived in the lowest altitude range - less than 1,600ft above sea level.

After taking into account other factors that could influence the results such as retirement age, the researchers found adults living in the lowest altitude range had a Body Mass Index (BMI), a height to weight ration of 26.6.

That compared to people who lived in the highest altitude range, who had a BMI of 24.2. A healthy BMI falls between 18.5 and 24.9.