People who live where the air is thinnest are less likely to be obese than those in low-lying areas, according to a new study. The
results don't mean people should move to higher altitudes to lose weight, said
study lead author Dr Jameson Voss.
But the work suggests that elevation may be part of obesity
puzzle. Based on data for more than 400 000 people in the US, researchers found
Americans living closest to sea level were four to five times more likely to be
obese, compared to people who live well above sea level in Colorado.
"I was surprised by the magnitude of the effect... I
wasn't expecting such a consistent pattern as what was emerging," said
Voss, from Uniformed Services University of the Health Sciences in Bethesda,
Obesity in the US
About 36% of American adults are obese, according to the US
Centers for Disease Control and Prevention (CDC). Rates vary across the
country, however, with a higher percentage of obese adults in southern states.
Western states, such as Nevada and Colorado, report the fewest obese adults.
The reasons behind the difference in obesity prevalence
between states are unclear, according to Voss and his colleagues, who published
their findings in the International Journal of Obesity. One possible
explanation, they write, is differences in elevation, which can affect appetite
hormones, growth and how many kilojoules the body burns.
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 kilojoules in their first few weeks.
Keeping the weight off
"That person would probably lose some weight during the
course of a three week vacation... It would in fact be an interesting question
whether that would sustain," said Beall, a professor of anthropology at
Case Western Reserve University in Cleveland.
To examine obesity rates at different altitudes, the
researchers combined information from several databases, including a telephone
health survey of 422 603 Americans from 2011.The researchers had information on
236 people who lived at the highest altitude of at least 3 000 meters (about 9 800
feet) above sea level.
Those people all
lived in Colorado and tended to smoke less, eat healthier and exercise more. The
researchers also had information on 322 681 people who lived in the lowest
altitude range - less than 500 m (about 1 600 ft) above sea level.
Findings in the study
After taking into account other factors that could influence
the results, the researchers found adults living in the lowest altitude range
had a Body Mass Index (BMI) - a measurement of weight in relation to height -
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, and
obesity is a score of 30 or more, according to the CDC. Voss and his colleagues
also found a drop in the risk of a person being obese was tied to every 200 m
(about 660 ft) increase in elevation.
"It provides some evidence that these associations
persist over the long term," Voss said. RETIREMENT PLAYS A ROLE? But Beall
cautioned that the new findings don't prove the higher altitude prevented
people from being obese.
People living in
For example, she said that other researchers have found that
people living in Colorado's higher altitudes move to lower altitudes when they
get sick with chronic diseases.
Voss said that he and his colleagues tried to adjust for
retirement and population loss, but they write that they were not able to see
how long each person actually lived at a certain elevation.
Beall told Reuters Health that it would be interesting to
take a closer look at the people living in Colorado, and to see whether their
obesity prevalence would change if they move to a lower altitude."I know
from my own self that when I come back to my own activities and diet, I come
back to my own weight too," she said.