NEW YORK (Reuters) -- Army soldiers who parachute are at increased risk of brain injury, according to a new study.

Fortunately, in most cases the head injuries are mild, researchers report in the Journal of Trauma.

But since moderate to severe brain injuries can have serious long-term consequences and the lasting effects of mild injuries is uncertain, the study's authors call for more research on brain injuries among paratroopers.

The study included more than 2,300 active-duty soldiers stationed at Fort Bragg, North Carolina. About four out of five of the soldiers were paratroopers.

Among the entire group, about 23 percent of the soldiers reported that they had experienced a traumatic brain injury while serving in the Army.

Most of the injuries were mild, with only two percent of soldiers reporting that they had lost consciousness for more than 20 minutes. And only 12 percent to 14 percent of the soldiers had been hospitalized for their injuries.

But paratroopers were much more likely than non-paratroopers to experience a traumatic brain injury while in the service. About 30 percent of paratroopers had such an injury compared with about 14 percent of non-parachuting soldiers.

Among paratroopers, about two out of three head injuries occurred while parachuting. "These results suggest that parachuting is a risk factor for mild traumatic brain injury in the Army," concludes a team led by Brian J. Ivins at the Defense and Veterans Brain Injury Center at Walter Reed Army Medical Center in Washington, D.C.

Paratroopers were somewhat more likely than other soldiers to have had a head injury before joining the army. This suggests that they may have been more likely to take risks than other soldiers, according to the authors.

In fact, paratroopers who had experienced a traumatic brain injury before enlisting were more likely to have a head injury as a soldier than paratroopers who had not had a pre-Army injury.

Ivins' team is continuing to study the soldiers at Fort Bragg to see what lasting effects, if any, traumatic brain injuries have on soldiers.

Investigations are also underway to see whether improved equipment can reduce paratroopers' risk of brain injury.