Beijing, China - Chinese researchers have reported, for the first time, a link between exposure to passive smoking and peripheral arterial disease (PAD) in a cohort of women who have never smoked [1]. Dr Yao He (Chinese PLA General Hospital, Beijing, China) and colleagues publish their findings online September 22, 2008 in Circulation.

"We found that compared with women who were not exposed to secondhand smoke [SHS], among women who were exposed to SHS, the risk of intermittent claudication was increased by 87% and risk of PAD—assessed by ankle-brachial index [ABI] <0.90—was increased by 47%, with significant dose-response relationships for both number of cigarettes exposed to and duration of exposure," they state.

In line with previous studies, He et al also found an increased risk of both coronary heart disease and stroke in the women exposed to secondhand smoke, with this being the first study to specifically report a positive association between SHS and ischemic but not hemorrhagic stroke.

"In China, only 4% of women are current smokers, but more than 50% of women are exposed to SHS," they note. "But most people [there] are unaware of the serious health hazards of SHS. Thus, urgent public-health measures are warranted to protect individuals from exposure to SHS."

Urgent public-health measures are warranted to protect individuals from exposure to secondhand smoke.

The researchers explain that China is the largest producer and consumer of tobacco in the world, with its 350 million smokers puffing their way through 30% of the globe's cigarettes. But awareness of the health hazards of either active or passive smoking is still low.

They set out to examine the relationship between SHS and cardiovascular diseases, particularly PAD and stroke, in older Chinese women (60 years or older) who had never smoked, from a population-based cross-sectional study in Beijing. SHS was defined as exposure to another person's tobacco smoke at home or in the workplace.

"Because the vast majority of women were never-smokers (87%), we had a unique opportunity to evaluate the association of SHS with risk of CVD, particularly PAD," they note.

After adjustment for 13 potential confounding factors, they found that women who had been exposed to SHS had a significantly higher risk of coronary heart disease (adjusted odds ratio 1.69, p<0.001) and ischemic stroke (OR 1.56, p=0.035) than those never exposed to SHS.

The adjusted odds ratios of PAD defined by intermittent claudication (IC), by ABI <0.90, and by either IC or ABI <0.90 were 1.87 (p=0.001), 1.47 (p=0.018), and 1.67 (p<0.001), respectively.

Dose-response relationships were found between SHS exposure amount (cigarettes per day) and duration (minutes per day) and increasing prevalence of CHD, ischemic stroke, and PAD.

"Our finding of a dose-dependent association of SHS with CHD is consistent with the literature," He et al explain. They also note that their findings with regard to stroke support previous studies, but that many of these did not investigate subtypes of stroke.

"This population based study is the first to report a positive association of SHS exposure with ischemic stroke but not hemorrhagic stroke among Chinese female nonsmokers."

An important advantage of the study, say He et al, was that PAD was diagnosed by ABI measurement. They explain that PAD is an underdiagnosed and undertreated condition in China: previous studies have shown almost 50% of PAD patients are asymptomatic, and most of them are unaware of their condition.

"To the best of our knowledge, this is the first study showing an increased risk of PAD with increasing SHS exposure," they note, adding that they believe their results are generalizable to similar populations in China.

"SHS exposure in women is highly prevalent in China. In addition to being a causal factor for CHD, SHS should be considered an important risk factor for ischemic stroke and PAD in Chinese women who never smoked," they conclude.