Exposure to air pollution increases the risk of dying from stroke say British researchers. A new review found a link with short-term exposure to carbon monoxide, nitrogen dioxide, sulphur dioxide and soot particles. The review shows a rising risk of hospital admission or death from stroke over the week following exposure, in line with higher concentrations of pollutants.

A second study from US researchers shows a possible link with anxiety in people recently exposed to air pollution. Among over 70,000 U.S. women in the study, those who lived in relatively polluted areas were more likely to report multiple anxiety symptoms.

The anxiety study, conducted by researchers at Harvard and Johns Hopkins University, showed a significant connection between exposure to fine particulate pollution and symptoms of anxiety for more than 70,000 older women (mean age of 70 years) in the contiguous United States. Bigger particles appeared to have no effects, interestingly, nor did living close to a major road. The connection was present over a variety of time periods from one month to fifteen years, but was stronger in the short term. This evidence shows a clear need for studies to be done in other demographic groups, and to elaborate on the biological plausibility of the connection.

The stroke article, meanwhile, is a meta-analysis of 103 studies conducted in 28 countries and including 6.2 million events. Researchers found that both gaseous and particulate air pollution had a “marked and close temporal association” with strokes resulting in hospital admissions or death.

The studies, published online March 24 in the BMJ, only link these factors; they do not prove that air pollution is the direct cause of either strokes or anxiety. There could be other explanations, said Melinda Power, a researcher at Johns Hopkins University, in Baltimore, who led the anxiety study.

She said her team included the other possible factors that they could account for, such as whether women lived in a big city, or had heart or lung conditions. “But you can’t account for everything,” said Power, who was with Harvard University at the time of the study.