U.S. troops sent to Iraq or Afghanistan are more likely to start a smokeless tobacco habit than their comrades who stay home -- especially if they see combat, a new study finds.

The findings, reported in the journal Addiction, follow other studies that have tied deployment and combat to health risks, including higher rates of smoking and drinking.

This adds to the list of things we're learning are associated with combat, said lead researcher Dr. Eric D.A. Hermes, of the Yale University School of Medicine in New Haven, Connecticut.

It's not fully clear why some troops take up smokeless tobacco after deployment. But Hermes suspects stress is involved.

That's because deployment with combat exposure was linked to a higher risk than deployment alone. And troops with symptoms of post-traumatic stress disorder (PTSD) also had an increased risk.

The findings come from the Millennium Cohort Study, an ongoing government project looking at the health effects of military service.

Of more than 45,000 personnel followed from 2001 to 2006, 2 percent started using smokeless tobacco during that time. Another 9 percent had already developed the habit, and kept it up.

Overall, troops who were deployed but did not see combat were almost one-third more likely to take up a smokeless tobacco habit than their non-deployed counterparts. Those odds were two-thirds to three-quarters higher for troops who were in combat or who deployed multiple times.

According to Hermes, those different levels of deployment can be seen as stand-ins for different levels of stress.

So it's possible that stress plays a role, he said.

Another finding gives weight to that idea. We also saw a relationship with PTSD symptoms, Hermes said.

Just under 4 percent of all troops had PTSD symptoms, based on a standard questionnaire. And they were 54 percent more likely to start using smokeless tobacco than troops without symptoms, Hermes and his colleagues found.

There are other factors that, along with stress, might push some deployed troops toward tobacco, according to Hermes.

You're not at home, you have more exposure to smokeless tobacco, you're around more people doing it, Hermes said. Maybe it's all these little things coming together.

MILITARY TOBACCO USE STILL HIGH

Past studies have found that while tobacco use in the military is declining, it's still higher when compared to the U.S. public as a whole. In 2005, almost 15 percent of military personnel said they'd used smokeless tobacco in the past year -- versus just three percent of Americans overall.

Smoking is the thing that everyone talks about, Hermes said. But there's also smokeless tobacco, and it seems to be related to the stress of combat.

Whether some troops are treating their stress with tobacco, or whether the tobacco somehow feeds the stress is not entirely clear, according to Hermes. There's still a chicken-and-egg question, he said.

But the findings suggest that doctors treating military personnel should ask not only about smoking habits, but any use of the smokeless forms of tobacco, Hermes said.

Tobacco products are widely available at U.S. military bases. A 2009 study commissioned by the Pentagon and the Department of Veterans Affairs recommended a phased-in ban on tobacco on military property. But whether that will ever happen remains up in the air.

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