Women in China who are exposed to pollution from cookstoves and highways face a greater risk of high blood pressure, researchers said Monday.

The study published in the Proceedings of the National Academy of Sciences focused on the role of black carbon, which after carbon dioxide is the second leading human-caused emission driving climate change.

Black carbon comes from burning wood, coal and fossil fuels. About half of all Chinese households cook with coal and wood, the researchers said.

The study involved 280 women living in a rural area of northwestern Yunnan province, with an average age of 52. Eighteen percent were overweight and four percent were obese at the start of the survey.

The women wore portable air samplers that collected air particulate matter (PM) smaller than 2.5 micrometers, a size commonly associated with adverse health effects.

Black carbon exposure was linked to higher blood pressure, a leading risk factor for heart disease.

"We found that exposure to black carbon pollutants had the largest impact on women's blood pressure, which directly impacts cardiovascular risk," said lead author Jill Baumgartner, an assistant professor at McGill University.

"In fact, black carbon's effect was twice that of particulate matter, the pollutant measured most often in health studies or evaluating cleaner cookstoves."

Furthermore, living within about 200 meters (yards) of a highway was associated with a threefold higher systolic blood pressure -- the greater of the two numbers that measure blood pressure -- than women who lived further from a highway.

"We found an indication that the cardiovascular effect of black carbon from biomass smoke may be stronger if there is co-exposure to motor vehicle emissions," said the study.

Reducing such exposure "should lead to a reduction in the adverse health and climate impacts of air pollution."

Previous studies in Latin America have shown that when older women switched from traditional open fire cookstoves to less-polluting chimney stoves, their blood pressure decreased.

"We found that black carbon from wood smoke negatively affects cardiovascular health, and that the health effects of wood smoke are exacerbated by co-exposure to motor vehicle emissions," said Baumgartner.

"Policies that decrease combustion pollution by replacing inefficient wood stoves and reducing traffic pollution will likely benefit both climate and public health."