A river has a main channel and side streams. A person's social position is the channel, while habits and health are the streams. Scientists traced which streams most strongly accelerate brain aging in people with low income, little education or from poor neighborhoods.
They took brain scans of 36,878 people and asked a computer to guess age from those scans. Then they compared the guessed age with the real one. In people with low income, the brain looked on average four months older than in wealthier people. It is as if the river flowed a little faster.
Blood sugar and blood pressure also turned out to be important streams. Alcohol, though, behaved strangely: in some people it seemed to slow aging, in others to speed it up. This means that income, education and neighborhood cannot be treated as one and the same. Now it is clear that shutting off the main stream, smoking, is the easiest thing to do, and that could help narrow the gap in brain health.
The average brain age gap among participants was about 3.4 years on T1-weighted images, comparable to the effect of a decade of smoking.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.