New study finds that secondhand smoke increases risk of stroke for nonsmokers

Nearly 800,000 people in the U.S. suffer a stroke each year. Stroke is responsible for one out of every 19 deaths in the U.S. and it is a leading cause of disability. A new study published in the American Journal of Preventive Medicine found that secondhand smoke (SHS) increases the risk of stroke by about 30 percent for nonsmokers.

Using data from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a national, population-based, longitudinal study investigating cardiovascular disease events and mortality endpoints among white (55 percent) and African American (45 percent) adults aged greater than 45 years, investigators found that even after adjustment for other stroke factors such as hypertension, diabetes, and heart disease, the 30 percent risk for nonsmokers remained.

The current study included almost 22,000 participants (38 percent African American, 45 percent male) with 23 percent reporting SHS exposure in the past year. During the period of April 2003 to March 2012, 428 strokes were reported. A further analysis of the type of stroke (ischemic vs. hemorrhagic) was performed and showed that most strokes were due to blockage of blood flow to the brain (352 ischemic, 50 hemorrhagic, and 26 strokes of unknown subtype).

The literature concerning adverse health effects of SHS is becoming clearer, although not all studies have replicated the association between SHS exposure and stroke. According to lead author Angela M. Malek, PhD, of the Department of Public Health Sciences, Medical University of South Carolina, Charleston, "Previous studies suffer from limitations in that few were prospective, adjustment for potential confounders has varied, stroke and SHS exposure have not been consistently defined, measurement and sources of SHS exposure have differed, stroke subtypes have not always been assessed, and some studies have been underpowered due to small sample size."

The strengths of the current study result from the use of a population-based sample of a large, prospectively followed, well-characterized group of people that includes a large proportion of African Americans and physician-adjudicated incident strokes.

"Our findings suggest the possibility for adverse health outcomes such as stroke among nonsmokers exposed to SHS and add to the body of evidence supporting stricter smoking regulations. Future research will need to investigate the role of cardiovascular disease risk factors in the association and explore potential exposure to additional environmental variables, such as ambient air pollutants, in relation to stroke." explained Dr. Malek.