Photo/Illutration Kyoto University Hospital (Asahi Shimbun file photo)

Stress brought on by gender inequality is affecting the thickness of women’s brains, according to a study that prompted one of the researchers to liken the result to “a big alarm to society.”

The study found that the outer thickness of the right part of women’s brains was slimmer than men’s in countries where gender inequality is an issue.

However, no substantial difference emerged in nations where gender inequality is not an issue.

The study by Kyoto University and other institutions covered 29 nations.

A member of the joint international research team called for follow-up studies to examine aspects of gender inequality that are affecting brain development in greater detail.

The team members examined magnetic resonance imaging (MRI) brain scans of 7,876 healthy men and women between the ages of 18 and 40. 

They correlated the data against national-level gender inequality metrics they calculated based on the World Economic Forum’s Gender Gap Index that is issued annually and the U.N. Development Program’s Gender Inequality Index.

Researchers found that differences between men and women in the thickness of the cortex, the outer layer of the cerebrum where nerve cells are concentrated, tended to be wider in countries with greater gender inequality.

This was particularly evident in the right hemisphere of the brain as the cortex was thinner in women than in men.

No gender difference was found in cerebral cortex thickness in gender-equal countries.

The gender difference in cortical thickness was larger in Japan, which ranked 12th among the 29 countries in the inequality metrics, than in Scandinavian nations, which filled the top rungs in gender equality rankings.

Researchers examined 68 regions of the cerebral cortex.

They found that gender differences in cortical thickness were larger in some of the regions that are related to aspects of emotional control, including resilience to adversity, responses to inequity, or negative social comparisons.

In those regions, the cortex was significantly thinner in women than in men in countries with greater gender inequality. 

Studies by other researchers have cited thinning and reduced volume of those regions in patients suffering from mental illnesses.

The latest research results indicate that continued exposure to an adverse environment under gender inequality could be having a potentially hazardous effect on women’s brains, the scientists said.

“Our study results are sounding a big alarm to society,” said Tsukasa Ueno, a program-specific assistant professor of psychiatry with Kyoto University Hospital, who took part in the research.

“To work out concrete measures, there should be follow-up studies for finding out which kinds of gender inequality are problematic for women’s brains and when precisely they have a big impact on brain development,” she added.

The research results were published in the Proceedings of the U.S. National Academy of Sciences (https://doi.org/10.1073/pnas.2218782120).

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