Non-smokers with both long-term exposure to second-hand cigarette smoke and narrowing of the artery that brings blood to the brain had three times the risk of developing dementia than people without either of those risk factors, according to a study led by a researcher at the San Francisco VA Medical Center.
“Other health risks from second-hand smoke have been demonstrated very well, but this is the first indication that there might be an indirect link between second-hand smoke and dementia among people with cardiovascular risk factors,” says lead author Deborah Barnes, PhD, MPH, a mental health researcher at SFVAMC and an assistant professor of psychiatry at the University of California, San Francisco.
The study, which appears in the online Advance Access section of the American Journal of Epidemiology, analyzed data from 970 participants in the Cardiovascular Health Cognition Study, a longitudinal study of risk factors for cardiovascular disease and dementia among adults 65 years or older that is funded by the National Institutes of Health. The authors looked at study participants who were lifelong non-smokers and did not have cognitive impairments when the study began, and followed them for five to six years.
According to Barnes, the researchers found no direct connection between dementia and length of exposure to second-hand smoke: “People with high levels of exposure, which we defined as more than 25 years of living with a smoker, had the same amount of risk as people with low levels.” But subjects with high levels of exposure combined with stenosis, or narrowing, of the carotid artery – the vessel in the neck that carries blood from the heart to the brain – had three times the risk of developing dementia.
“It was the combination of the two that seemed to matter,” says Barnes. She notes that carotid artery stenosis, which is caused by a buildup of plaque on the inside of the artery, often has no symptoms, “so someone might have an increased risk of dementia and not even know it. It’s yet another argument for trying to keep cardiovascular disease risk factors under control.”
Barnes cautions that the study is the first to indicate a link between second-hand smoke, carotid artery stenosis, and dementia, “so it is important to confirm these findings in another study population. We don’t want to leap too far in assuming a cause-and-effect relationship.”
She says that if the results are confirmed, “then they will provide additional support for all of the efforts we have made to limit people’s exposure to second-hand smoke.”
Co-authors of the study are Thaddeus J. Haight, MA, of the University of California, Berkeley; Kala M. Mehta, DSc, MPH, of SFVAMC and UCSF; Michelle C. Carlson, PhD, of Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Lewis H. Kuller, MD, of the University of Pittsburgh; and Ira B. Tager, MD, MPH, of UC Berkeley.
The study was supported by funds from the National Institutes of Health, the National Heart, Lung, and Blood Institute, the National Institute for Neurological Disorders and Stroke, and the Flight Attendants Medical Research Institute.
SFVAMC has the largest medical research program in the national VA system, with more than 200 research scientists, all of whom are faculty members at UCSF.
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