October 25th, 2010
04:52 PM ET
Here's yet another reason to stop smoking: It elevates the risk of Alzheimer's disease and vascular dementia, according to a new study.
An analysis of more than 20,000 men and women found a 157 percent heightened risk of Alzheimer's disease in people who had smoked more than two packs of cigarettes a day. For vascular dementia, the second most common form of dementia, these smokers had a 172 percent increased risk.
"Dementia is a disease that crops up in late life, and that becomes clinically apparent, but I think people really need to think about risk factors for it over the life course," said Rachel Whitmer, study co-author and research scientist with Kaiser Permanente Division of Research in Oakland, California.
The study, sponsored by Kaiser Permanente, is published in the Archives of Internal Medicine.
Researchers say the association between smoking and various forms of dementia is strong, but they do not know exactly why. It has been shown before that people who smoke are more likely to have hypertension and cerebral vascular disease, as well as inflammation, Whitmer said. Smoking may contribute to the damage of brain blood vessels in addition to brain cells, she said.
The data came from Kaiser Permanente Northern California members surveyed between 1978 and 1985. At that time, they were between ages 50 and 60. Diagnoses of various forms of dementia among these people were made from 1994 to 2008, and researchers took that information from electronic health records. The participants in this study were all alive and still members of the health plan in 1994.
Researchers found that associations with the development of the disease are more modest among smokers who use up fewer than two packs a day, but still significant. Those who smoked a half-pack to one pack a day had an overall 37 percent elevated risk of dementia, and those who smoked between one and two packs had a 44 percent heightened risk, compared to non-smokers.
But this could be an underestimation, because some smokers who would have developed dementia died before diagnosis, said Kenneth Hepburn, associate dean for research at the Emory University School of Nursing, who was not involved in the study.
The reported risk of dementia among heavy smokers is also likely an underestimation because many of those people will die before they're old enough to develop dementia, he said.
While the elevated risk for various forms of dementia was shown for those smoking two packs a day in midlife, smoking less than half a pack of cigarettes a day, or having smoked in the past, did not appear to raise the risk compared with nonsmokers.
Hepburn found the study compelling, and noted that it incorporated an ethnically diverse population of both men and women.
"This gives great confidence in saying this kind of heavy smoking has some kind of association – and it looks like a fairly strong association – with the development of the disease," he said.
One limitation of the study is that researchers collected data only about smoking habits among middle-aged people; it did not look at what happened among those who had quit after the initial survey, Whitmer said.
The research speaks to what the Alzheimer's Association Maintain Your Brain campaign is promoting: that brain health has a lot to do with overall health, Hepburn said.
"The brain is part of the body, it’s part of the whole and if you assault parts, it’s going to have an impact on the whole," he said.
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