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Association between High Altitudes and Low Rates of Obesity

Living at high altitudes may be associated with a lower risk of obesity…. 

Investigators analyzed members of the U.S. military were who overweight and considered at risk for becoming obese, to assess the risk of obesity at high altitude regions versus low altitude regions. Researchers used body mass indexes (BMI) to find those considered overweight but not obese, defined as having a BMI of at least 25 but less than 30.

A total of 98,009 service members were identified and observed between January 2006 and December 2012, during outpatient medical visits, for a mean of 3.2 years. During this time, researchers noted when participants had a change in BMI categorizing them as obese or when an official diagnosis of obesity occurred. Researchers compared results between study participants assigned to a high altitude post (defined as higher than 1.96 km above sea level) and those at low altitudes (defined as below 0.98 km below sea level).

They found that service members stationed at a high altitude had a lower hazard ratio (HR) of incident obesity diagnosis than those stationed at low altitudes (HR=0.59; CI 95%, 0.54 to 0.65). After controlling for factors including enlistment BMI, branch of service, time in service, occupation, age, sex, race/ethnicity, and housing allowance, those at high altitudes were found to have a 41% lower rate of obesity  (CI 95%, 35% to 46%; P<0.001). Looking at altitude as a continuous variable, researchers found a 6% lower hazard of obesity (HR=0.94; CI 95%, 0.91 to 0.96) per kilometer above sea level.

The prevalence of civilian obesity was also strongly related to the military obesity incidence. After incorporating prevalence from 3 civilian datasets (Behavioral Risk Factor Surveillance System, National Health and Nutrition Examination Survey, and Reasons for Geographic and Racial Differences in Stroke) high altitude duty assignment remained a protective association (HR=0.83; CI 95%, 0.73 to 0.95) as compared to low altitude. This model predicted a 10% increase in obesity incidence for every 1% increase in regional obesity prevalence (HR=1.10; CI 95%, 1.09 to 1.11).

Additional studies are needed to investigate exactly what causes those at higher altitudes to be less likely to become obese. Some believe this may be attributed to outdoor lifestyles such as mountain biking, hiking and skiing. Other explanations may be that lower levels of oxygen may have an effect on metabolism.

Practice Pearls:
  • Altitude may have a direct influence on overall obesity risk
  • Overweight individuals living in high altitudes were associated with less risk of becoming obese compared to those living at a low altitude
  • Further studies are needed to investigate the underlying mechanism behind this association

Voss JD, Allison DB, Webber BJ, Otto JL, Clark LL. Lower Obesity Rate during Residence at High Altitude among a Military Population with Frequent Migration: A Quasi Experimental Model for Investigating Spatial Causation. PLoS ONE. 2014;9(4):e93493. http://www.plosone.org/article/info%3Adoi/10.1371/journal.pone.0093493