Scientists have found a hormone linked to post-traumatic stress disorder (PTSD). A mouse study found the fat hormone, adiponectin, could potentially be used to help people recover from fearful experiences.

PTSD is a mental health problem brought on by a very distressing event. PTSD patients often suffer from flashbacks of the event, and have trouble sleeping due to nightmares. Around 8% of people are affected by the anxiety disorder, which is commonly found in army veterans. Up to 15% of retired US army personnel suffer from PTSD. Researchers from the University of Texas Health Science Center at San Antonio say that current treatments for PTSD are ineffective, or temporary with high relapse rates.

The researchers carried out tests on mice to find a biological mechanism which speeds up recovery following fearful experiences. They focused on the hormone adiponectin, a protein which helps to break down fatty acids in the body.

The mice were trained to expect a mild electric shock when placed in a cabinet. After four to six days, all of the mice showed fear when entering the cabinet. The scientists then placed the mice into the cabinet, but did not administer the shock, and observed how long the mice showed fearful behaviour for.

The results of the study, published in Molecular Psychiatry, showed mice deficient in adiponectin were scared for longer, when placed into the cabinet. When the researchers injected these mice with adiponectin, they overcame their fear quicker.

This suggests adiponectin is a biological mechanism linked to fear response. "Once the threat is no longer there, the fear should go away, but in PTSD it keeps flashing back," said Xin-Yun Lu, senior author of the research.

"In the PTSD animal model, the circulating adiponectin is low, data suggest. If the genes encoding adiponectin and its receptor are disrupted, the mice extinguish fear responses much slower. If adiponectin levels are elevated in the brain, the mice get extinction faster."

People with low levels of adiponectin could be at greater risk of developing PTSD if they are involved in a traumatic event, researchers say. They added that while it will be years before this research translates into a treatment, it is a promising avenue for further research.

"To date, medication treatments for PTSD have been of limited benefit," said Alan Peterson, of the UT Health Science Center and director of the Consortium to Alleviate PTSD. "Dr Lu's work holds significant promise for the development of new, more effective medication treatments for PTSD."