Science and Health

US research links heavy smoking with Alzheimer's disease

(Xinhua)
Updated: 2010-10-26 11:08

LOS ANGELES - Middle-aged chain smokers face greater risk of developing Alzheimer's disease, or dementia, US researchers have found in a new study.

The conclusion was based on analysis of data concerning 21,123 ethnically diverse people who were surveyed between 1978 and 1985, when they were 50 to 60 years old.

During an average follow-up of 23 years, 25.4 percent were diagnosed with dementia, including Alzheimer's (1,136 people) or vascular dementia (416 people), which is the second most common form of dementia after Alzheimer's disease. Vascular dementia is caused by damage to the arteries in the brain.

Compared with non-smokers, those who smoked more than two packs of cigarettes a day in midlife had a "dramatic increase" in the incidence of dementia - more than a 157 percent increased risk of developing Alzheimer's disease and a 172 percent increased risk of developing vascular dementia, according to the study published in the October 25 online edition of the Archives of Internal Medicine.

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Former smokers and people who smoked less than half a pack a day did not appear to be at increased risk of Alzheimer's or vascular dementia, the researchers noted.

The associations between smoking and dementia did not change even after adjusting for race or gender, high blood pressure, high cholesterol or heart attack, stroke or weight, the researchers added.

"We found that people who reported heavy smoking in midlife had more than a 100 percent increase in risk of Alzheimer's disease and vascular dementia," said lead researcher Rachel A. Whitmer, a research scientist in Kaiser Permanente's Division of Research in Oakland, Calif.

"We have known that smoking is a risk factor for cancer, stroke and cardiovascular disease," she said. "This adds to the evidence that what is bad for the heart is bad for the brain."

Smoking, an established risk factor for stroke, may contribute to the likelihood of vascular dementia by causing small clots in the brain, the researchers explained.

Smoking also contributes to oxidative stress and inflammation, which may be linked to the risk of developing Alzheimer's disease, according to the researchers.

A link between Alzheimer's and smoking has been shown before, but this new study pinpoints the specific risk for middle-age smokers for developing both Alzheimer's and vascular dementia, the researchers stresed.