New recruits enter the Army with roughly the same rates of mental problems as their civilian peers, but those disorders can persist for longer amid the demands of service than in civilian life, new research suggests.

These conclusions, drawn in two papers published Thursday by the journal Depression and Anxiety, help to explain a puzzle that has nagged the military during the Iraq and Afghanistan wars. Experienced soldiers have reported higher rates of mental problems than young men and women who do not enlist, even though soldiers have historically been more mentally fit than the general population.

The new research, which draws on surveys of more than 38,000 men and women in basic training, suggests that the higher rates of mental problems are rooted in the rigors of service, not in the loosening of enlistment standards. The surveys were anonymous.

Enlistees “are not much different from civilians” in terms of mental health, said Anthony J. Rosellini, a postdoctoral fellow at Harvard and lead author of the paper on mental disorders. “We suspect what’s going on is that disorders that appeared in childhood or adolescence might become more persistent in the context of the demands of the Army.”