Elderly people exposed to secondhand smoke for 30 years or more were 30 percent more likely to develop dementia than older adults who were not exposed to secondhand smoke, according to researchers at the University of California at Berkeley.

HealthDay News reported May 1 that researcher Thaddeus Haight and colleagues conducted a six-year evaluation of 985 people with no cardiovascular disease, dementia, or exposure to secondhand smoke and 495 people with similar health attributes who experienced long-term exposure to secondhand smoke.

"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."

Researchers are now looking at how exposure to smoking affects dementia directly.

The study also noted that secondhand-smoke exposure combined with cardiovascular disease nearly doubled the risk of dementia.

The study was presented at the annual meeting of the American Academy of Neurology.