New research from Harvard and Emory University suggests that mood swings in menstruating women can be due to low levels of the hormone estrogen.

According to Mohammed Milad from Harvard University, women are more at risk for anxiety and depression. In men, the hormone testosterone is converted into estrogen in the brain and so they have stable levels of the hormone, something which doesn't happen in women.

Studies conducted on the effects of levels of estrogen and fear response in females (human and rats) show that low levels of the hormone increases fear. Participants in these studies were exposed to fear via moderate shocks or puffs of air on their eyes or neck. Researchers found that response to fear was lower when the participants had higher levels of estrogen.

Researchers say that birth-control pills containing estrogen could be used to treat people with Post Traumatic Stress Disorder (PTSD).

Sexually abused women are at a higher risk of PTSD than sexually abused men because of the hormonal changes that occur during monthly periods, researchers say.

One study found that sexually abused women who took birth-control pills after the attack were less depressed than those women who did not. Some 111 women were interviewed in this study. Researchers found that women who took a combination pill Ogestrel (which includes both estrogen and progesterone) were better at dealing with the trauma than women who took Plan B (which contained only estrogen).

Researchers say that the morning-after pills can be used to reduce some of the fear after an attack.

Changing outlook

The new studies have looked beyond biases that occur in the field of neuroscience.

According to Larry Cahill, professor of Psychology at the University of California, researchers have always tried to avoid gender differences for social and scientific reasons. Cahill said that researchers assume the brain works in the same way in both males and females, which is not true.

“The single biggest bias in neuroscience research is the belief that sex differences are insignificant or small. This [research] is the latest salvo in a barrage of information saying to the field that sex differences are real, and should affect how we treat clinical disorders in men and women,” he said.

Cahill says that understanding of gender differences in the brain should help treatments that are custom-made for women, and that takes monthly periods in to account.

The study was published in Biological Psychiatry.