Exposure to secondhand tobacco smoke increases the risk of developing dementia

May 2 2007

Exposure to secondhand tobacco smoke increases the risk of developing dementia, according to research that will be presented at the American Academy of Neurology's 59th Annual Meeting in Boston, April 28, May 5, 2007.

For the study, researchers evaluated 3,602 people age 65 and older in the Cardiovascular Health Study. Of those, 985 people had no cardiovascular disease, no dementia, and were never smokers. A total of 495 people reported their lifetime secondhand smoke exposure, with an average of about 28 years of exposure. Then the researchers evaluated which participants developed dementia over a six-year period.

Based on preliminary results, the study authors found that elderly people with high lifetime exposure to secondhand smoke were approximately 30 percent more likely to develop dementia than those with no lifetime secondhand smoke exposure. High exposure was defined as more than 30 years of exposure to secondhand smoke.

"We are still conducting analyses to control for other factors that may be influencing these results, but this finding potentially implicates lifetime exposure to secondhand tobacco smoke as a risk factor for dementia in older adults," said study author Thaddeus Haight of UC Berkeley.

The study also found that exposure to secondhand smoke resulted in a greater occurrence of dementia for people who had not been diagnosed with cardiovascular disease but who had detectable abnormalities of their carotid arteries, based on carotid ultrasound imaging, compared to those without these underlying abnormalities. These abnormalities included narrower carotid arteries and thicker carotid arterial walls, and serve as indicators of preclinical cardiovascular disease and are risk factors for stroke. People with these underlying conditions and high lifetime exposure to secondhand smoke were nearly two-and-a-half times as likely to develop dementia as those with no secondhand smoke exposure and no indications of carotid artery disease.

"This is one of the first studies to look at the risk of dementia in people who never smoked, but were exposed to secondhand smoke," Haight said. "These results show that secondhand smoke is associated with increased risk of dementia, even in people without known risk factors for dementia related to diagnosed cardiovascular disease."

The study investigators used statistical methods to assess the associated risk of exposure to secondhand smoke independent of its known effects on clinically diagnosed cardiovascular disease.

"The fact that there were more people in this study population who were not diagnosed, but had underlying cardiovascular disease compared to people who were diagnosed points to the health risks associated with lifetime exposure to secondhand tobacco smoke in a potentially wider segment of the elderly population," said Haight.

Haight said the study findings provide additional evidence of the hazards of secondhand smoke and provide additional support for policies that seek to reduce the public's exposure to tobacco smoke.