Do Women Age Slower Than Men?

Sex differences have been noted in many brain areas. A recent study investigated sex differences in how our brains age. A normal human brain loses volume, cortical thickness and synapses as it ages. The brain is metabolically demanding. It utilizes 20 to 25 percent of the total body glucose consumption rate, but is only 2 percent of body weight. Aging is related to a decline in general metabolism, including the brain. A decrement of brain metabolism is not benign. A more youthful brain shows more metabolism than an older one.

In a recent study¹, the researchers used PET imaging to look at metabolism in the brains of more than 200 healthy men and women between 20 and 82 years old. They used machine learning to predict a brain’s age using data from the male subjects. Machine learning was able to predict the participants’ ages with high accuracy, there was a 0.89 correlation between predicted age and actual age for males.

Interestingly, this was not the case for female participants! When they fed the trained machine learning algorithm data from the female subjects, the correlation between actual and predicted age was much weaker. The predictions were consistently younger for the female brains, about 4 years on average. For example, a female who is 70 years old is equivalent to a 66 year old male. The data suggests that throughout the adult life span, the normal female brain is more youthful.

What does that mean in terms of abilities as we age? The more youthful a brain is, the more resilient it will be as it ages. Therefore, women should show more resilience to age-related decrements. That is precisely what the Baltimore Longitudinal study of aging found. Women outperformed men on many cognitive tasks². The differences in brain metabolism could also be a marker for neurocognitive decline and diseases such as Alzheimer’s disease.

Why are there sex differences in brain metabolism? Although the exact reasons are not yet known, the authors proposed that hormones might be the culprit. Estrogen has been shown to enhance plasticity which may be related to the adaptive youthful brain metabolism in females. When estrogen plummets post-menopause, so does brain metabolism. Unfortunately, this menopause-related reduction in estrogen can be detrimental for some women. Dr. Brinton’s research shows that the drop in brain metabolism is steepest for women who carry a particular gene variant called APOE4³.

Future research might answer many of these poorly understood questions. It would be interesting to discover ways to slow down the decrease in brain metabolism.