The study, to be undertaken by the Army and the National Institute of Mental Health, will cover 90,000 active-duty soldiers and all new Army recruits, 80,000 to 120,000 per year, New York Times reported.

The recruits are to answer confidential surveys that might include questions on whether they owned motorcycles, used drugs or liked to bungee-jump, Colonel Bruce Shahbaz, a retired Army lieutenant colonel and one of the three main authors of a recent Army suicide report, said.

There will be cognitive tests to measure reactions to stress as well as an in-depth look at a recruit’s family background and genetics.

"We've never been at war for as long as we've been, and we don't know the effects of that," Shahbaz said, referring to the US-led wars in Afghanistan and Iraq.

"It will give us an assessment of someone's cognitive style and whether they have a history that draws them to high -risk behaviors," New York Times quoted Thomas R Insel, the director at the National Institute of Mental Health.

The military says the people who enlist to serve their country have always included plenty of adrenaline addicts, which recruiters say is a good thing when troops are needed to jump out of airplanes and go on raids in Afghanistan.

But military researchers say they have been compelled to take a deeper look at the psychological demographic of an all-volunteer force during the most prolonged period of combat in American history.

Shahbaz said the Army wants to know whether risk- takers are more likely to commit suicide or die in accidents, and whether a predisposition to risk-taking is increased by combat.

There were a record 160 active-duty suicides in the US Army in the year from October 1, 2008, to September 30, 2009, the Times said.