a paradox that baffles scientists

It is one of the cruelest paradoxes of modern neurology: women are diagnosed with the Alzheimer’s disease almost twice as many times as men. And the question in this case was obligatory: why? The first theories They pointed to brain agingpointing out that women’s brains deteriorate faster. But now, everything has changed radically.

A published study in Proceedings of the National Academy of Sciences (PNAS) Not only does it disprove this hypothesis, but it reveals just the opposite: the brains of healthy men seem to age and shrink faster. But even so, the expected effect is not what we see in the prevalence of the disease.

Until now, studies on sex differences in brain aging have produced conflicting results. While some suggested a greater loss of gray matter in men, others pointed to a more pronounced deterioration.

The method. To clarify this picture, an international team of scientists has carried out one of the largest analyzes to date. To do this, they analyzed 12,638 longitudinal brain MRIs of 4,726 cognitively healthy participants (2,181 men and 2,545 women).

The participants, in this case, aged between 17 and 95, underwent at least two brain scans at an average interval of 3.3 years. This allowed the researchers to observe not a still photo, but actual structural changes in the brain over time, controlling for factors such as head size.

Further deterioration. The results, after adjustments, were surprisingly clear: Men experienced greater volume and thickness reduction in more brain regions than women.

Men showed a more pronounced decrease in cortical thickness in regions such as the cuneus, lingual gyrus, and parahippocampal. They also showed a greater reduction in surface area in the fusiform and postcentral cortex. For example, the postcentral cortex, responsible for processing sensations such as touch and pain, decreased at an annual rate of 0.20% in men compared to 0.12% in women.

Furthermore, in older adults it was seen that men also showed greater contraction in key subcortical structures such as the caudate, putamen and nucleus accumbens. In contrast, women only showed greater surface area reduction in the superior temporal sulcus and greater ventricular expansion in old age.

The conclusion. The study’s main conclusion is as compelling as it is puzzling: sex differences in age-related brain decline are “unlikely” to explain why women have a higher prevalence of Alzheimer’s diagnoses. Amy Brodtmann, a researcher at Monash University, agrees, adding that if these changes were responsible for Alzheimer’s, we would expect to see greater deterioration in women in areas crucial for memory, such as the hippocampus, something the study did not find in its main analyses.

This forces the scientific community to look for other explanations. The results suggest that the higher prevalence of Alzheimer’s in women is likely due to factors other than brain atrophy due to age.

There are nuances. The authors of the study themselves recognize that the disease is a complex phenomenon. One of the limitations of the study is that the sample of participants had higher educational levels than the general population, a known protective factor against Alzheimer’s, which may not be fully representative.

Furthermore, the study introduces a fascinating nuance. When the researchers adjusted the data not for chronological age, but for remaining life expectancy, several of the differences disappeared. In this scenario, women even showed a greater decline in hippocampal volume. This could indicate that terminal, near-death brain changes play an important role, but more research is needed to confirm this.

Images | Natasha Connell

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