Socioeconomic conditions amplify pollution-related bone loss

Postmenopausal women living in socioeconomically disadvantaged neighborhoods experience substantially greater bone mineral density loss from nitrogen oxide air pollution, according to a recent study. 

A team at the Icahn School of Medicine at Mount Sinai in New York City analyzed dual-energy x-ray absorptiometry (DEXA) data from 9,041 postmenopausal women enrolled across 40 U.S. clinical sites. They found that neighborhood-level socioeconomic status significantly modified the association between nitrogen oxide exposure and bone mineral density loss, with women in lower-income neighborhoods faring worse. 

"These findings show that air pollution does not affect everyone equally," said study lead Diddier Prada, MD, in a press release from the university. "Women living in socioeconomically disadvantaged neighborhoods experienced substantially greater bone loss despite similar pollution exposure." 

Osteoporosis and related fractures impose a substantial burden on postmenopausal women, the authors noted, with approximately 2.1 million fracture cases reported annually in the U.S. and roughly $22 billion in direct healthcare costs each year. In previous work, Prada and colleagues showed for the first time that exposure to air pollution is associated with decreased bone mineral density (BMD). However, the extent to which socioeconomic status contributes to pollution-related bone damage remains unclear, the researchers noted. 

To bridge the gap, the group analyzed data from 4,202 randomized clinical trial participants and 4,839 observational study participants, totaling 9,041 women with both DEXA and air pollution data at enrollment. They calculated exposure among the groups to ambient concentrations of nitric oxide (NO), nitrogen dioxide (NO2), and sulfur dioxide (SO2) averaged over one-, three-, and five-year periods preceding the DEXA scans. Neighborhood-level socioeconomic status (nSES), individual income, and educational attainment were evaluated as potential effect modifiers. 

According to the results, a 10% increase in NO2 was suggestively associated with 1.4 to 3.8 times greater BMD loss in low versus high nSES participants across all sites. For example, one-year lumbar spine BMD loss per 10% NO2 increase was β = −0.047 in the low nSES compared with β = −0.013 in the high nSES group (p = 0.001). Similarly, suggestive associations were also observed for NO. 

For income, NO exposure was suggestively associated with lumbar spine bone loss across all averaging periods, with women in the lowest income group showing approximately twice the bone loss per unit exposure compared with higher-income women. No interactions with income were observed for SO2, the researchers reported. 

Lastly, lower-educated women showed greater NO-related lumbar spine bone loss, while SO2 showed the opposite pattern: associations were stronger among higher-educated women, according to the findings. 

“Our findings underscore how environmental and social conditions work together to influence long-term bone health,” Prada said. 

Ultimately, reducing social inequities may improve the bone health of older women living in areas with high air pollution, the group wrote. Additional studies are needed to generalize the findings to younger women and men, as only older women were analyzed, the researchers concluded. 

The study was published June 30 in Frontiers in Public Health and is available here.