Cigarette smoke damages the lungs, but it also wreaks havoc in the brain, a study in mice suggests. Signs of Alzheimer’s disease increased in the brains of animals that breathed cigarette smoke for four months, scientists report February 19 in Nature Communications.
The relationship between smoking and Alzheimer’s in people is murky. Some evidence from the 1990s suggested that smoking actually protected people against Alzheimer’s, presumably by stimulating nicotine-detecting brain cells. More recent studies have found that smoking ups the odds of the disease.
To see what cigarettes do to the brain, scientists led by Claudio Soto of the University of Texas Medical School at Houston turned to mice. In animals bred to show signs of Alzheimer’s, cigarette smoke (one cigarette’s worth in air the mouse breathed for an hour, five days a week) worsened aspects of the disease. Compared with mice that weren’t exposed, mice exposed to smoke had several signs of Alzheimer’s: they had more amyloid beta plaques, a higher load of abnormal tau protein and more severe inflammation in their brains.
The scientists don’t know yet how cigarette smoke causes these changes, or whether a similar process happens in people.