A new study exploring the link between post-traumatic stress disorder and traumatic brain injuries found that Marines who sustained a mild head injury while serving in Iraq and Afghanistan were more likely to develop the condition, The Los Angeles Times reported.

After following more than 1,600 Marines between 2008 and 2012, researchers found that Marines who exhibited symptoms of PTSD prior to deployment and sustained a mild brain injury during combat had an increased risk of testing positive for PTSD once they returned from service. The news source stated that the risk rose by 23 percent to 34 percent, while the risk for those who tested negative for PTSD before deployment remained unchanged. About 327 of the 1,600 Marines studied – roughly 20 percent – experienced a head injury. 

According to the news outlet, the researchers suggested that the main factor for the increase is that bomb blasts tend to lead to psychological trauma. 

Earlier this year, The Los Angeles Times reported that servicemembers who have a history of insomnia are also at a higher risk for developing PTSD, as well as depression. Researchers suggested that treating the sleep disorder before the servicemembers deploy might help alleviate future PTSD symptoms.