July 29, 2008 -- Nonsmokers who are married to someone who smokes have a greatly increased risk for stroke, a finding that further underscores the dangers of secondhand smoke.

Researchers reporting in the September issue of the American Journal of Preventive Medicine say the risk varies depending on whether the nonsmoking spouse has smoked in the past.

Secondhand smoke makes a person more likely to develop heart disease, but until now, few studies have linked such exposure to stroke risk. One trial suggested that a husband's smoking increased a wife's chances for a stroke, but only if the woman also smoked.

For the current study, M. Maria Glymour, ScD, of the Harvard School of Public Health, and colleagues looked at the smoking habits of the spouses of more than 16,000 stroke-free married adults aged 50 and older who were enrolled in the Health and Retirement Study (HRS).

The study only evaluated cigarette use, not cigars or pipe tobacco. Researchers followed the participants for about nine years to document the occurrence of first stroke. During the study period, there were 1,130 first strokes reported.

Being married to a current smoker increased the risk of a first stroke by 42% among those who never smoked.

The risk of stroke was higher for former smokers who were married to current smokers. Former smokers who had a smoking spouse had a 72% increased risk for stroke compared with those who were married to a never-smoker.

The good news, researchers say, is the risk can be cut if the spouse kicks the habit. Participants who had never smoked and who were married to a former smoker had nearly the same stroke risk as never-smokers married to never-smokers.

"These findings indicate that spousal smoking increases stroke risk among nonsmokers and former smokers. The health benefits of quitting smoking likely extend beyond individual smokers to affect their spouses, potentially multiplying the benefits of smoking cessation," Glymour writes in the journal article.