Short and long-term exposure to air pollution from vehicle exhaust or burning coal is associated with high blood pressure, according to a review of 17 studies.
"Since the 1990s, a hypothesis of air pollution leading to hypertension risk was proposed by many researchers," said senior author Tao Liu of the Guangdong Provincial Center for Disease Control and Prevention in Guangzhou, China.
The researchers analyzed 17 studies of air pollution and hypertension, defined as blood pressure higher than 140/90 millimeters of mercury (mm Hg). In total, the studies included more than 80,000 people with high blood pressure and more than 220,000 people without it.
They found that short-term exposure to sulfur dioxide from burning fossil fuels and to particulates like dust and dirt in the air were associated with high blood pressure risk, as was long-term exposure to nitrogen dioxide, which comes from power plants and vehicle exhaust.
Short-term exposure to ozone and carbon monoxide were not tied to blood pressure levels, as reported in the journal Hypertension.
Air pollution can cause inflammation and oxidative stress which may lead to changes in the arteries, the authors write.
"There is a linear relationship between air pollution and hypertension, which indicated that even a very low level of air pollution might induce hypertension risk," Liu told Reuters Health by email. "Therefore, everyone should be concerned about the effects of air pollution on their blood pressure even if there is a very low air pollution level in their living environment."
"However, it is impossible to remove all of the air pollutants from the environments," Liu said.
The studies in this review tie pollution to high blood pressure but don't prove that one causes the other, Liu said.
More studies, especially multi-center studies, are needed to investigate a causal relationship between air pollution and high blood pressure, Liu said.
"Without a clear mechanism we cannot conclude that pollution 'causes' hypertension," said Dr. Gaetano Santulli of Columbia University Medical Center in New York, who was not part of the new study. "However, we should recall (going back to 1954) that epidemiological evaluations provided strong statistical support in linking cigarette smoking and cancer."
Hypertension affects more than three million people in the U.S.
Quitting smoking, eating healthy, reducing intake of sodium and sugar, reducing chronic stress, and exercising regularly can help reduce the risk of high blood pressure, Santulli told Reuters Health by email.