Overweight U.S. service members are 41 percent less likely to transition to clinical obesity when stationed at military facilities located at high altitude, according to a new study published today in the peer-reviewed journal, PLoS One.
The quasi-experimental, retrospective study assessed the health records and migration patterns of nearly 100,000 enlisted service members in the active component of the U.S. Army and Air Force with at least two years in the services from records in the Defense Medical Surveillance System. The study period was January 1, 2006 to December 31, 2012. The service members also had no prior diagnosis of obesity between the time of enlistment until entry into the study.
High altitude duty stations were of interest because multiple experimental studies show hypoxia can decrease food consumption and cause weight loss. The study's authors sought to evaluate an overweight population who would be at risk of progression to obesity during a single duty assignment. The burden of obesity is a particular concern to the U.S. military, threatening its operational capacity and diminishing the ranks of qualified applicants for the services. Excess weight diagnoses have markedly increased with a burden of $1 billion in annual healthcare costs to the Department of Defense health system, according to the study.
"This is the strongest evidence to date that moving to high altitude provides long-term obesity protection," said Air Force Captain Jameson Voss, the study's lead author who initially embarked on the project during his preventive medicine training at the Armed Forces Health Surveillance Center. Capt. Voss, a physician with a master's in Public Health, completed the work where he now serves in the 711th Human Performance Wing's U.S. Air Force School of Aerospace Medicine.
"Not only does this study confirm the results of earlier studies but it expands and strengthens previous results by evaluating and demonstrating this association in military members and is the first study to demonstrate this by observing individuals over time. It also offers evidence that overweight service members can stall or prevent the onset of obesity by residing in high altitude locations," added Dr. Leslie L. Clark, the paper's senior author and a senior epidemiologist for General Dynamics Information Technology contracted to work at the Armed Forces Health Surveillance Center.
Another significant finding from the study showed that service members were still 41 percent less likely to develop obesity when the authors adjusted the rate for factors that included baseline body mass index at time of enlistment, age, sex, race and ethnicity, occupation, housing allowance, time in service, and branch of service. When the results are unchanged after adjusting for measured characteristics, it suggests unmeasured characteristics were also similar between those assigned to high or low altitude.
The study also discovered differences in obesity incidence in different low altitude regions suggesting there are other geographic factors to explore aside from altitude. In addition, the study compared new cases of obesity in military members with state level obesity among civilians. Although these were connected, the relationship between altitude and new cases of obesity appeared even stronger than the state level patterns among civilians.
"As a large uniform population with extensive and available demographic, location, health and job related records, the military provides an unparalleled source for investigation of residential health effects," Capt. Voss said. "There are stronger implications for understanding the causal effect of location because service members do not freely choose where to live, but are administratively assigned to these locations."
- Jameson D. Voss, David B. Allison, Bryant J. Webber, Jean L. Otto, Leslie L. Clark. 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 DOI: 10.1371/journal.pone.0093493
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