High blood pressure may cause harmful brain changes in people as young as 40, a study suggests.

In the report, published online Nov. 2 in Lancet Neurology, researchers measured blood pressure in 579 men and women whose average age was 39, then examined their brains with magnetic resonance imaging. After adjusting for smoking, hypertension treatment and total cranial volume, they found that higher systolic blood pressure — the most common form of hypertension — was associated with decreases in gray matter volume and significant injury to white matter. Moreover, there was a dose-response relationship: The higher the blood pressure, the greater the visible changes.