Researchers say there may be a biological explanation for the fact that women are twice as vulnerable to stress disorders like depression and post-traumatic stress disorder, compared to men.

Studying stress signaling systems in animal brains, neuroscience researchers found that females are more sensitive to low levels of an important stress hormone and less able to adapt to high levels than males.

"This is the first evidence for sex differences in how neurotransmitter receptors traffic signals," said study leader Rita Valentino, Ph.D. "Although more research is certainly necessary to determine whether this translates to humans, this may help to explain why women are twice as vulnerable as men to stress-related disorders."

Valentino’s research team studied the response of lab rats to the corticotropin-releasing factor (CRF), a hormone that organizes stress responses in mammals. When responding to a swim stress test, they found that female rats were more receptive to CRF than their male counterparts.

Experts say that since CRF regulation is disrupted in stress-related psychiatric disorders, this study may be relevant to the underlying human biology.

Natural methods of reducing stress include exercise, relaxation and breathing exercises, tai chi, yoga and meditation.