Air Pollution Tied to Higher Hospitalization Risk for PD, Other Neurological Disorders

Air pollution was found to be significantly associated with an increased risk of hospital admissions for several neurological disorders, including Parkinson disease (PD), Alzheimer disease (AD), and other dementias, according to study findings published Monday in The Lancet Planetary Health.

Led by researchers at the Harvard T.H. Chan School of Public Health, the study serves as the first nationwide analysis to examine the link between fine particulate (PM_2.5) pollution and neurodegenerative diseases in the United States. As the study authors highlight, accumulating evidence links PM_2.5 to premature mortality, cardiovascular disease, and respiratory disease, but less is known of its influence on neurological disorders.

Aiming to investigate the effect of PM_2.5 exposure on development of PD, AD, and related dementias, researchers conducted a longitudinal study of a population-based nationwide open cohort that included all US fee-for-service Medicare beneficiaries (aged ≥ 65 years) from January 1, 2000 to December 31, 2016 (N = 63,038,019), with no exclusions. After collecting hospital admissions data from the study cohort, researchers linked each Medicare recipient with estimated PM_2.5 concentrations by zip code based on mean annual predictions from a high-resolution model.

Researchers utilized Cox-equivalent Poisson models with parallel computing to estimate hazard ratios (HRs) for first hospital admission for PD or AD and related dementias, adjusting for potential confounders, such as socioeconomic status, in the health models.

Of the study cohort, researchers identified 1 million cases of PD and 3.4 million cases of AD and related dementias based on primary and secondary diagnosis billing codes. In their findings, for each 5 microgram per cubic meter of air (μg/m³) increase in annual PM_2.5 concentrations, a 13% increase (HR = 1.13; 95% CI, 1.12–1.14) in risk of first-time hospital admissions for PD and AD and related dementias was observed.

Moreover, even in areas that had safe levels of PM_2.5 exposure according to current US Environmental Protection Agency standards (annual average of 12 μg/m³ or less), this risk remained elevated. At-risk populations were noted to be women, white people, and urban populations, with the highest risk for first-time PD hospital admissions indicated to be among older adults in the northeastern United States. Older adults in the Midwest were shown to face the highest risk for first-time AD and related dementias hospital admissions.

"The 2020 report of the Lancet Commission on dementia prevention, intervention, and care has added air pollution as 1 of the modifiable risk factors for these outcomes," said co-lead study author Xiao Wu, doctoral student in biostatistics at Harvard T.H. Chan School of Public Health, in a statement. "Our study builds on the small but emerging evidence base indicating that long-term PM_2.5 exposures are linked to an increased risk of neurological health deterioration, even at PM_2.5 concentrations well below the current national standards."

Reference

Shi L, Wu X, Yazdi MD, et al. Long-term effects of PM2.5 on neurological disorders in the American Medicare population: a longitudinal cohort study. Lancet Planet Health. Published online October 19, 2020. doi:10.1016/S2542-5196(20)30227-8