But new research finds one factor that influences the rate at which our brains age is largely outside our control: our socioeconomic status.
"We provide evidence that there exists a powerful relationship between an individual's present environment and their brain," a research team led by Micaela Chan and Gagan Wig of the University of Texas–Dallas writes in the Proceedings of the National Academy of Sciences.
In its study, middle-aged adults of lower socioeconomic status "exhibited signs of both functional and structural brain aging earlier in adulthood" than their better-off peers.
"Engaging and resourceful environments associated with higher socioeconomic status may provide a buffer or delay against aging," the researchers write. "Inadequate health conditions associated with lower socioeconomic status environments (such as exposure to toxins and poorer nutrition), together with continual stress, may accelerate the aging process."
The study featured 304 participants between the ages of 20 and 89, who were recruited in the Dallas-Fort Worth area. Their socioeconomic status was determined by their years of education and occupation.
Using neuroimaging, the researchers evaluated participants' brains in two ways, measuring "functional network organization and cortical gray matter thickness." They found both measures demonstrated greater aging in people of lower socioeconomic status, even after accounting for demographic differences and personal health.
The results raised an obvious question: Was this a long-term effect of a difficult life, or can it be traced back to their childhoods? To find out, the researchers noted the childhood socioeconomic status of 168 of the participants (which was estimated using their parents' education level as a marker).
Taking that information into account did not change their results, which suggests the more pronounced neural aging appears to be cumulative.
While the reasons for this aren't entirely clear, the researchers point to some obvious possibilities. People who are struggling to get by tend to have less access to nutritious food, high-quality health care, and opportunities for "continuous and sustained learning," they write.
Besides living in a "less stimulating environment," they are subject to "environmental and social stressors," which can have long-term negative effects on the brain. A 2014 study found African-Americans age more rapidly than whites, presumably due to the stress of dealing with racism.
We've long been told that a mind is a terrible thing to waste. Perhaps we need to remember it's also a terrible thing for a mind to waste away.