Jill Baumgartner, who performed the study while a doctoral student at University of Wisconsin-Madison, says the study involved 280 women in an ethnic minority called the Naxi who lived in a remote area of Yunnan province in China. The women wore a portable device that sampled the air they were breathing for 24 hours.
The Naxi live in compounds with a central, free-standing kitchen that often has both a stove and a fire pit, Baumgartner says.
"I spent a lot of time watching women cook in these unvented kitchens, and within seconds, my eyes would burn, it would get a little difficult to breathe," Baumgartner says in a statement.
Many of the women are exposed to this smoke for several hours a day and even if the cook stove is vented, a second fire is often burning for heat, Baumgartner, now at the Institute on the Environment at the University of Minnesota, says.
Baumgartner and colleagues associated higher levels of indoor air pollution with a significantly higher blood pressure among women age 50 and older.
The study, published in the journal Environmental Health Perspectives, found small-particle pollution raises blood pressure over the short term by stimulating the nervous system to constrict blood vessels, but in the long term, the particles can cause oxidative stress, which also raises blood pressure.