Second-hand smoke increases the risk of stroke by about 30 per cent for nonsmokers, researchers say.
Even after adjusting other stroke factors such as hypertension, diabetes and heart disease, the 30 per cent risk for nonsmokers remained, the team from Medical University of South Carolina, Charleston said.
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"Our results suggest the possibility for adverse health outcomes such as stroke among nonsmokers and supports stricter smoking regulations," said lead researcher Angela M Malek in the American Journal of Preventive Medicine.
The study included almost 22,000 participants with 23 per cent reporting second-hand smoking exposure.
During April 2003 to March 2012, 428 strokes were reported; a further analysis of the type of stroke was performed and showed that most strokes were due to blockage of blood flow to the brain.
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The literature concerning adverse health effects of second-hand smoke is becoming clearer, the authors said.
"Future research will need to explore potential exposure to additional environmental variables, such as ambient air pollutants in relation to stroke," Dr Malek said.