Specific components of air pollution were linked to increased depression risk in older adults, new research suggested. 

A cohort study of nearly 24 million adults showed that long-term exposure to fine particulate matter (PM_2.5) overall and to four of its six major components individually was associated with increased likelihood of late-life depression development. Sulfate, elemental carbon, and soil dust were the main contributors to the association, with a fourth component, ammonium, also showing relevance. 

The likelihood for depression was increased with exposure to more than one of these components and for individuals with neurologic or cardiometabolic comorbidities. 

“These findings suggest that regulation of specific PM_2.5 components may help reduce depression risk, particularly among vulnerable older populations,” Yanling Deng, PhD, Rollins School of Public Health, Emory University, Atlanta, Georgia, and colleagues wrote. 

The results were published online on December 22 in JAMA Network Open. 

Hunting Culprit Components

Although previous research has shown a link between fine particulate matter and depression, the current study sought to assess which components may be causing this association. 

The nationwide, population-based cohort analysis included data for nearly 24 million older Medicare beneficiaries (mean age at baseline, 76 years; 55% women; 89% White, 7% Black) from 2000 to 2018.

A spatiotemporal model was used to assess annual concentrations over a 5-year window of PM_2.5 mass as well as its six major components: elemental carbon, ammonium, nitrate, sulfate, soil dust (largely silicon), and organic carbon.

The 5-year mean level of PM_2.5 was 10.2 µg/m³. The component with the highest annual level was sulfate, followed by organic carbon.

Late-life depression was identified by Medicare claims. More than 5.5 million participants developed depression during follow-up, 97% of whom had at least one comorbidity, with hypertension the most common.

‘Meaningful Implications’

Results from single-pollutant models showed that exposure to 5-year average concentrations of PM_2.5 was associated with increased odds of depression (hazard ratio [HR], 1.02), as were concentrations of sulfate (HR, 1.05), elemental carbon and soil dust (HR, 1.03 for both), and ammonium (HR, 1.01).

A combination of all six of the major components had an even greater association, with each one-quartile increase linked to increased risk for depression (HR, 1.07), with soil dust, sulfate, and elemental carbon the primary contributors.

“Although the individual-level effect sizes were modest, such small relative increases in risk may have meaningful population-level implications given the widespread exposure to air pollution and the high burden of depression among older adults,” the investigators wrote.

The associations between depression and the pollutant components (especially soil dust, sulfate, and elemental carbon) were even greater in participants with cardiometabolic comorbidities, such as hypertension and congestive heart failure, and those with neurologic comorbidities, such as dementia, Alzheimer’s disease, and stroke.

There was no association between total PM_2.5 and increased depression risk in participants without comorbidities.

“Our findings underscore the necessity for stricter regulation of ambient PM_2.5 emissions, particularly from fossil fuel combustion and traffic sources,” the researchers wrote.

The study was funded by grants from the National Institutes of Health. The investigators reported having no relevant financial relationships.