A new study found that long-term air pollution exposure is linked to weight gain in women, particularly those in their late 40s and 50s. According to a recent news release from the University of Michigan, researchers discovered that women exposed to higher levels of fine particles, such as nitrogen and ozone, experienced increases in body size and composition measurements.

Researchers analyzed data of 1,654 women, with an average age of 50, from the Study of Women’s Health Across the Nation from 2000 to 2008. Annual air pollution exposures were assigned by linking residential addresses with hybrid estimates of air pollutant concentrations. The researchers examined the association between the amount of pollution the women were exposed to and their body size and composition measures.

Exposure to air pollution was linked to higher body fat, higher proportion of fat and lower lean mass among midlife women. For example, body fat increased by 4.5%, or about 2.6 pounds in those exposed to the most pollution. On a positive note, researchers discovered that high levels of physical activity did mitigate weight gain and offset the effects of pollution.

According to the New York Post,  Xin Wang, of the University of Michigan School of Public Health and the lead study author, said since the research focused solely on middle-aged women, the findings can’t be generalized to younger—or older—women or men at this time.