A large international study reveals that the natural process of brain shrinkage differs between sexes. In men, it occurs at a faster rate and affects many areas of the brain, while in women the process is slower and limited to fewer regions.
The human brain naturally shrinks with age, but in people with Alzheimer disease this process is accelerated and particularly severe.
Although women are diagnosed with the disease at twice the rate of men, knowledge about how biological sex affects brain volume decline throughout life remains limited.
The study was conducted at a university in Norway and published in the journals PNAS and Nature.
As part of the research, more than 12,000 brain scans from 4,726 participants aged 17 to 95 were examined.
All participants had normal cognitive function.
Each participant underwent at least two MRI scans with an average interval of three years.
The Gender Gap in the Brain
After accounting for natural differences in brain size between men and women, a clear pattern emerged.
Among men, a broader and more significant decline in brain volume was observed, encompassing many regions, including large parts of the cerebral cortex, which is responsible for higher cognitive functions such as memory, language and decision making.
Among women, by contrast, the reduction in volume occurred in a smaller number of regions, and cortical thickness remained relatively stable over the years, suggesting a milder and slower degeneration process.
If women’s brains were deteriorating more rapidly, this could have explained the higher rates of Alzheimer disease among women, but the data present a different picture.
The findings indicate that there are real biological differences in how the brain ages in men and women.
However, the researchers emphasize that the results should be interpreted with caution.
These are small but consistent reductions in brain volume that do not necessarily indicate functional impairment.
Long term follow up studies are needed to examine how these differences are reflected in cognitive function, memory and the development of age related neurological diseases.
Does Brain Shrinkage Mean Dementia
The researchers found that differences between men and women were evident not only in overall brain volume but also in additional structural features, including cortical thickness, surface area of the cerebral cortex, and the volume of many subcortical regions involved in sensory and cognitive functions.
One notable finding stood out.
No difference between the sexes was found in the rate of change observed in the hippocampus, the region responsible for memory and learning, which is known to play a central role in dementia and neurodegenerative diseases.
Only at very advanced ages did women begin to show a faster decline in hippocampal volume, after accounting for women’s longer life expectancy.
According to the research team, this may simply reflect a natural delay in the aging process rather than an explanation for the higher prevalence of Alzheimer disease among women.
The brain, similar to age related changes in the skin, undergoes a natural process of shrinkage and loss of nerve cells.
However, there is not necessarily a direct connection between a decrease in brain volume and a decline in cognitive function.
In some cases, certain cognitive processes may actually improve with age.
This is a more complex mechanism that depends on the brain regions involved, the speed of the process, and age.
In principle, there is a correlation between dementia and brain shrinkage, but this is not the only measure.
The extent of shrinkage can be measured using brain MRI scans, but it is important to understand that when patients are told there is brain shrinkage, it does not necessarily mean a pathological process.
In most cases, this is a natural part of aging and does not necessarily indicate dementia.
Although brain shrinkage is observed in dementia, not every case of shrinkage indicates dementia.
Gaps That Disappear With Age
When researchers compared men and women with similar expected life expectancy, much of the difference in the rate of brain volume decline nearly disappeared.
This suggests that some of the observed gaps between the sexes may stem from general differences in life expectancy rather than from unique biological processes.
Despite decades of brain research, science still suffers from significant gender bias.
According to data cited by the researchers, only about 5 percent of studies published in neurology or psychiatry in 2019 addressed the effect of sex on brain structure.
As a result, there is still no definitive picture.
Different studies point to conflicting findings, with some identifying sharper declines in brain volume among men and others among women.
The current study seeks to refine understanding of the issue and suggests that while structural differences between the sexes do exist, they are not necessarily the direct cause of the higher prevalence of Alzheimer disease among women.
The researchers note that distinguishing between the effects of biological sex and genetic, environmental, and social factors is a particularly complex scientific challenge.
Large scale and long term studies in this field are rare, and therefore understanding of brain degeneration mechanisms remains partial.
A scientific review published in 2023 already warned against ignoring the influence of sex on brain aging processes, arguing that failure to address this factor could lead to serious public health consequences and create a disproportionate burden on women’s health.
The conclusion emphasizes that individuals who undergo brain MRI scans and discover shrinkage should not draw hasty conclusions.
This is a natural age related process that does not necessarily indicate cognitive impairment.
There are additional significant factors beyond shrinkage itself that can influence the development of dementia.