Human Brains Are Getting Bigger, So Why Are Dementia Rates Rising?

More and more people are minding their brain health, especially if they've seen friends or family members struggle with cognitive decline. From dementia prevention games to memory supplements and optimizing sleep, we're learning how to put the brain first. 

The finding comes from a cross-sectional study published in the journal JAMA Neurology1. The research team analyzed data from the Framingham Heart Study cohort to explore trends in cranial and brain volumes and cortex thickness.

The 3,226 participants included in the study were born between 1930 and 1970, and MRI scans took place between 1999 and 2019, when the participants were an average age of 57 years old. As a prerequisite, they all had to be free from dementia or stroke history at the time of the scan.

The research team states that larger brain volumes indicate larger brain development and potentially greater brain reserve. They hypothesize that this leads to a decline in dementia. 

"The volume of the region hippocampus is important, it plays a direct role in the preservation of memory," adds board-certified neurologist and integrative medicine doctor Dr. Romie Mushtaq, M.D.

But this increase in brain size comes with a paradox, given that dementia is statistically on the rise. I asked board-certified psychiatrist and neuroscientist Dave Rabin, M.D., Ph.D., to explain how the brain could be getting larger, offering an improvement in dementia rates, yet the opposite is happening. 

"The human brain is getting larger and smaller in different ways simultaneously," he says frankly. The shrinking he refers to is called synaptic pruning. This process takes place when the parts of the brain left underutilized get trimmed down, while other parts of the brain become larger and tighter the more they're utilized. 

So if you zoom out and look at increasing rates of dementia, you'll realize it doesn't necessarily have to do with brain size—we now know that is working in our favor, if anything. Rather, it's social and environmental contributors that continue to elevate Alzheimer's risk.

Rabin identifies social isolation, lack of connections, and a deficiency in continuous learning as key reasons behind this increasing trend. Mushtaq agrees, adding high levels of stress and nutrition challenges for some groups to the list. 

A recent study indicates that the human brain may be expanding, potentially offering a promising opportunity for reducing dementia rates. Nonetheless, experts emphasize the importance of addressing the social and environmental factors currently driving the increase in dementia cases.