Secondhand Smoke Boosts Risk for Alzheimer's

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Researchers say that dementia is 30% more common in people with long exposures to secondhand smoke.

(HealthDay News) -- Breathing in secondhand smoke could raise your risk for Alzheimer's disease and other forms of dementia, a new study finds.

It's the first study to link secondhand smoke to this form of mental deterioration, said lead researcher Thaddeus Haight, a research statistician at the University of California, Berkeley.

"There have been studies that have shown that exposure to secondhand smoke is related to subclinical cardiovascular disease and clinical cardiovascular disease," Haight noted. "There also have been studies showing that atherosclerosis, hardening of the arteries, is related to an increased risk of dementia."

The current study completes the loop by showing that inhaling someone else's smoke increases the incidence of dementia, he said.

"This study attempts to look at the relationship between cardiovascular disease and dementia and also looks at the independent, direct effects of tobacco on the nervous system," Haight said. "There is an alternative pathway other than cardiovascular disease with potential neurotoxic effects. Secondhand smoke could affect the neurodegenerative process behind dementia and may lower the threshold for dementia-like symptoms."

Haight was scheduled to present the findings this week at the annual meeting of the American Academy of Neurology, in Boston.

In their study, the Berkeley team evaluated data on more than 3,600 participants enrolled in a long-running study of cardiovascular health. They compared 985 never-smokers with no cardiovascular disease and no dementia to 495 people who reported an average of 28 years of lifetime exposure to another person's smoking.

A six-year evaluation revealed that elderly people exposed to secondhand smoke for 30 years or more were about 30 percent more likely to develop dementia than those without such exposure, the researchers said.

"We're now looking at how smoke affected dementia directly and are also attempting to separate out the effects of secondhand smoke that occur through clinical vascular disease," Haight said.

Analysis of the data showed that the combination of long-term exposure to secondhand smoke and the presence of cardiovascular disease nearly doubled the risk of dementia. Long-term exposure to secondhand smoke alone increased the risk of dementia by about a third.

The study also found a greater incidence of dementia in people who were not diagnosed with cardiovascular disease but who had detectable abnormalities of their carotid arteries, the main arteries to the brain, on ultrasound images. People exposed to secondhand smoke who had those abnormalities (such as narrowed carotid arteries) were 2.5 times more likely to develop dementia as those with no carotid abnormalities and no secondhand smoke exposure.

The study results provide support for efforts to reduce exposure to secondhand smoke, such as bans on smoking in restaurants and bars, Haight said.

"It's reasonable to suppose that anything that is bad for your heart is bad for your brain, so it is no great surprise that secondhand smoke could be responsible for development of carotid artery disease and dementias of all kinds," said Bill Thies, vice president for medical and scientific affairs at the Alzheimer's Association.

The exact degree of danger is somewhat unclear, because the data in the report are not complete, but the danger does exist, Thies said.

"This study is an important addition to the overwhelming evidence of serious health harms from secondhand smoke," said Matthew L. Myers, president of the Campaign for Tobacco-Free Kids. "It underscores the need for all states to pass comprehensive smoke-free laws covering all workplaces and public places."

Published:
Week of May 13 - May 20, 2007
By:
Ed Edelson
Permalink:
http://www.AlzWeek.com/node/254

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1940096/

Barrett JR. Neurology: Dementia and Secondhand Smoke. Environ Health Perspect. 2007 August; 115(8): A401.

Secondhand smoke is known to be associated with cardiovascular disease, which in turn is a known risk factor for dementia, but little research has examined the latter end point with regard to secondhand smoke. Research presented at the 28 April–5 May 2007 annual meeting of the American Academy of Neurology now suggests that increased risk of Alzheimer disease and other forms of dementia may well belong on the long list of potential health effects from chronic exposure to secondhand smoke.

“When we started this study, . . . we knew of the likely pathway through cardiovascular disease, but we were also interested in an independent pathway from secondhand smoke [directly] to dementia,” says principal investigator Thaddeus Haight, a senior statistician at the University of California, Berkeley. That direct pathway did not bear out, but the team did make a new discovery regarding the cardiovascular link.
Haight and his colleagues analyzed health data for elders with and without cardiovascular disease that had been collected through the Cardiovascular Health Study, a national study of cardiovascular disease risk factors in adults older than 65. Of the 3,602 participants who had been evaluated for dementia, 985 had no history of cardiovascular disease or symptoms of dementia and had never smoked, and 495 reported an average of nearly 28 years of secondhand smoke exposure.

The group most highly exposed to secondhand smoke—those with a lifetime exposure of more than 30 years—had a 30% greater risk for developing dementia compared with the no-exposure group. Within the highly exposed group, people with subclinical cardiovascular disease (defined as narrowing of the carotid artery) had an even higher risk, nearly 2.5 times that of the no-exposure group. “There weren’t really any independent effects due to secondhand smoke exposure alone, but there were effects through a pathway other than clinical cardiovascular disease,” says Haight. “In people with indications of subclinical disease, . . . the greater the exposure to secondhand smoke, the more elevated the risk of dementia.”

“These results are definitely not surprising; they are completely in line with what we know about heart health and brain health—that both are extremely interconnected,” says Maria Carrillo, director of medical and scientific relations for the Alzheimer’s Association national office. “Anything that makes it more difficult for your heart to pump blood through your body will ultimately affect how your body pumps blood into the brain. That compromised brain blood volume really makes a difference after years of exposure.”
Haight and his colleagues are currently working to confirm their findings. He says, “What would be interesting from this work that we’ve done so far is to extend it to look at the risk of dementia in those with a history of secondhand smoke exposure who have diabetes or hypertension.”