Heavy smoking in middle age more than doubles the risk of Alzheimer’s disease and other types of dementia later in life, according to one of the first long-term studies to examine the issue and reported in the Chicago Tribune.
Smoking has a clear effect on the heart and lungs, but whether it also damages the brain has been controversial. The study, published Monday in the Archives of Internal Medicine, overcomes some of the obstacles that have made it difficult to assess such a link. For example, some previous research suggesting that smoking doesn’t cause dementia mostly examined elderly people only for a short period of time.
To get a more complete look, researchers in Finland, Sweden and the Oakland-based research division of the health plan Kaiser Permanente followed 21,123 middle-aged Kaiser members who participated in a survey between 1978 and 1985, and then studied the participants for an average of 23 years.
After controlling for other factors that can contribute to dementia — such as education level, race, age, diabetes, heart disease and substance abuse — the study found a significant link with heavy smoking in middle age.
Compared to nonsmokers, people who smoked two packs a day or more had a 114 percent increased risk of dementia (more than double) while people who smoked one to two packs a day had a 44 percent increased risk. Those who smoked half to one pack a day had a 37 percent increased risk.
Middle-aged people who described themselves as former smokers did not appear to have an increased risk of later dementia.
One way that smoking might increase the risk of dementia would be via the narrowing of blood vessels in the brain, a process that leads to the well-established increased risk of stroke, said Rachel A. Whitmer, a research scientist at Kaiser Permanente’s Division of Research and the principal investigator in the study.
However, even people who smoked heavily in midlife and did not have any subsequent strokes were at higher risk for dementia, Whitmer said.