Wednesday, May 04, 2005

Obesity and war

First, obesity and influenza. Now, obesity and war. What's next, Revere? Obesity and Lakoff? Obesity and Tasers? I'll let you guess. Right now it's "obesity and war."

From the American Heart Association's 45th Annual Conference on Cardiovascular Disease Epidemiology and Prevention, April 30, 2005, a paper by Anne Marie Johnson: Association Between Exposure to Combat Stress and Behavioral and Physical Risk Factors in Aging Men: The Life Course SES (LCSES) Study (via Medpage Today). War makes you fat. And more likely to smoke and drink heavily.

Studying a group of almost 5400 men, 22% of whom were combat veterans of WWII, Korea or Vietnam, University of North Carolina epidemiologists found odds ratios of 1.9 (95% Confidence Interval [CI] 1.5 - 2.3) for smoking and 4.0 (2.9 - 5.7) for smoking when comparing combat veterans to non-veterans, after adjusting for age, race, and education levels.

Here's a (very) brief primer on what these numbers mean. The odds ratio is a way to estimate the risk ratio, for example, the risk of smoking for those with a history of combat compared to non-combat. Since this is an estimate, just like a political poll is an estimate, we need some idea of how "stable" it is in the sense that if we were to take another sample of combat and non-combat men we might get a different odds ratio. The confidence interval is a way to get a feel for how much that estimated odds ratio would "bounce around" given repeated samples (technically, the 95% confidence interval is a "coverage probability," the range of numbers included 95 out of every 100 calculations of a confidence interval, but that's not very important; just think of it as a "margin of error" like in a poll). In this case we have the odds for smoking among combat veterans four times the odds for smoking among non-veterans (odds ration of 4.0). If we were to sample repeatedly we might see odds ratios that moved around a bit, the more extreme values being 2.9 on the low end and 5.7 on the high end. The most likely value is the estimate given, 4.0. Odds ratios with confidence intervals that don't include 1.0 (equal odds for both the combat and non-veteran groups) are sometimes called "statistically significant" but that kind of bright line is now discouraged in epidemiology. The width of the confidence interval is much more informative about how stable the estimate is. Very wide estimates connote a fairly unstable estimate.

Back to the subject. What about obesity, then? Here the difference was between combat veterans and non-combat veterans (not non-veterans). Those who fought on battlefields had odds ratios for obesity of 1.5 (CI 1.2 - 1.9) and odds ratios of 1.3 for having a larger waist circumference (CI 1.1 - 1.6). Thus, even among veterans, those who saw combat tended towards obesity and bigger waist sizes. In the conference abstract I saw no definitions of these outcomes, so we will have to wait for a published paper for details (which could be important). Here's what the authors thought was important:
Because this group appears to be at such high risk to develop behavior linked to cardiovascular risk factors, said Dr. Johnson, clinicians might want to keep a close eye on patients who have engaged in battle, no matter how long ago. Memories of combat "is such a pervasive thing and maybe they don't have ways to talk about it," Dr. Johnson said. "It impacts their psychology. It's a chronic and persistent stressor."

"One of the strengths of our study is that we had the two control groups," Dr. Johnson said in an interview. By comparing combat veterans to non-combat veterans, she explained, it diffused the notion that all veterans coped with their military experiences the same. Another strength, she said, was the research team looked at these men decades after they had engaged in combat, not shortly after their release from the military, suggesting their experiences had very long-lasting effects.
And here's what I think is important. These data are a reminder that the effects of war are pervasive and almost always bad. But for their combat experience early in life, a significant percentage of these men would be living happier and healthier lives. We took them as young men, and for those not killed or maimed, we distorted and misshaped their lives. How could it be otherwise?

If the CDC can go on a campaign against dietary factors that increase the risk of obesity (and they should), why can't they also go on a campaign against another public health scourge, war?

Sometimes to ask a question is to answer it. Too bad.