Heavy smoking doubles Alzheimer's disease, dementia risk

Heavy smoking in midlife is associated with a 157 percent increased risk of developing Alzheimer's disease and a 172 percent increased risk of developing vascular dementia, according to a Kaiser Permanente study published in the Archives of Internal Medicine.

This is the first study to look at the long-term consequences of heavy smoking on dementia.

Researchers followed an ethnically diverse population of 21,123 men and women from midlife onward for an average of 23 years. Compared with non-smokers, those who had smoked more than two packs of cigarettes a day had more than a 157 percent increased in risk of Alzheimer's disease and 172 percent increased risk of vascular dementia during the mean follow-up period of 23 years. Vascular dementia, the second most common form of dementia after Alzheimer's disease, is a group of dementia syndromes caused by conditions affecting the blood supply to the brain.

"This study shows that the brain is not immune to the long-term consequences of heavy smoking," said the study's principal investigator, Rachel A. Whitmer, Ph.D., a research scientist with the Kaiser Permanente Division of Research in Oakland, Calif. "We know smoking compromises the vascular system by affecting blood pressure and elevates blood clotting factors, and we know vascular health plays a role in risk of Alzheimer's disease."

Researchers analyzed prospective data from of 21,123 Kaiser Permanente Northern California members who participated in a survey between 1978 and 1985. Diagnoses of dementia, Alzheimer's disease and vascular dementia made in internal medicine, neurology, and neuropsychology were collected from 1994 to 2008. The researchers adjusted for age, sex, education, race, marital status, hypertension, hyperlipidemia, body mass index, diabetes, heart disease, stroke, and alcohol use.

"While we don't know for sure, we think the mechanisms between smoking and Alzheimer's and vascular dementia are complex, including possible deleterious effects to brain blood vessels as well as brain cells," said study co-author Minna Rusanen, MD, of the University of Eastern Finland and Kuopio University Hospital in Finland.

This study is the latest in a series of published Kaiser Permanente research to better understand the modifiable risk factors for dementia. This ongoing body of research adds to evidence base that what is good for the heart is good for the brain, and that midlife is not too soon to begin preventing dementia with good health. The other studies led by Whitmer found that a large abdomen in midlife increases risk of late-life dementia, elevated cholesterol levels in midlife increase risk of Alzheimer's disease and vascular dementia, and low blood-sugar events in elderly patients with type 2 diabetes increase dementia risk. Another Kaiser Permanente study led by Valerie Crooks of Kaiser Permanente in Southern California found that having a strong social network of friends and family appears to decrease risk for dementia.