Air pollution linked to rise in Parkinson’s, Alzheimer’s and other neurological disorders in Americans: Study
Researchers have found a significant link between air pollution and neurological disorders among Americans in a massive study of more than 63 million older US adults. Air pollution was notably associated with an increased risk of hospital admissions for several neurological disorders, including Parkinson’s disease, Alzheimer’s disease and other dementias, in the long-term study led by experts from the Harvard TH Chan School of Public Health.
The team -- which also includes researchers from Emory University’s Rollins School of Public Health and Columbia University’s Mailman School of Public Health -- analyzed 17 years (2000-2016) of hospital admissions data from 63,038,019 Medicare recipients in the US and linked these with estimated PM2.5 concentrations by zip code.
Taking into account potential confounding factors like socioeconomic status, they found that, for every 5 micrograms per cubic meter of air (μg/m3) increase in annual PM2.5 concentrations, there was a 13% increased risk for first-time hospital admissions both for Parkinson’s disease and for Alzheimer’s disease and related dementias. This risk remained high even below supposedly safe levels of PM2.5 exposure, which, according to current US Environmental Protection Agency (EPA) standards, is an annual average of 12 μg/m3 or less.
“Our study provides strong epidemiological evidence that long-term exposure to air pollution is significantly associated with a higher risk of neurological health deterioration, even at PM2.5 concentrations less than the current national standards,” write authors in their analysis published in The Lancet Planetary Health.
Worldwide, neurological disorders are the leading group-cause of disability and the second leading group-cause of death, posing an urgent and substantial worldwide public health challenge. Parkinson’s disease and Alzheimer’s disease and related dementias are the most prevalent neurodegenerative diseases. Globally, an estimated 6 million people have Parkinson’s and 44 million people have Alzheimer’s and related dementias.
The Global Burden of Diseases, Injuries and Risk Factors Study 2016 analysis estimated that, since 1990, the prevalence of Parkinson’s disease has increased by 145% and Alzheimer’s disease and related dementias have increased by 117%, say experts. “The prevalence of these conditions is expected to continue to increase due to lengthening life expectancy. As no cure exists yet for these conditions, the identification of modifiable risk factors, such as environmental exposures, should be a top research priority,” explain investigators.
The team argues that air pollution is a known risk factor for poorer human health, and concern is mounting that air pollution increases the risk for neurological disorders. “Research suggests that air pollution might contribute to the potential onset of neurodegeneration via mechanisms such as oxidative stress, systemic inflammation, and neuroinflammation, among others. There is also evidence that air pollution might exacerbate disease progression by accelerating these biological pathways or worsening intermediate processes. Therefore, the first hospital admission with a relevant diagnosis code is occurring sooner than expected,” write authors.
They add, “We aimed to investigate the effect of long-term PM2.5 exposure on the development of Parkinson’s disease or Alzheimer’s disease and related dementias.” Between January 1, 2000, and December 31, 2016, of 63,038,019 individuals who were aged 65 years or older during the study period, the researchers identified 1 million cases of Parkinson’s disease and 3.4 million cases of Alzheimer’s disease and related dementias based on primary and secondary diagnosis billing codes.
“Specifically, for each 5 μg/m³ increase in annual PM2.5 concentrations, the hazard ratio was 1.13 for first hospital admission for Parkinson’s disease and 1.13 for first hospital admission for Alzheimer’s disease and related dementias,” the findings state.
Among other findings, the report reveals that women, White people, and urban populations were particularly susceptible. The highest risk for first-time Parkinson’s disease hospital admissions was among older adults in the northeastern US. For first-time Alzheimer’s disease and related dementias hospital admissions, older adults in the Midwest faced the highest risk.
Based on the results, the team suggests that for the aging American population, improving air quality to reduce PM2.5 concentrations to less than current national standards could yield substantial health benefits by reducing the burden of neurological disorders.
“Our US-wide study shows that the current standards are not protecting the aging American population enough, highlighting the need for stricter standards and policies that help further reduce PM2.5 concentrations and improve air quality overall,” says the co-senior author of the study, Antonella Zanobetti, a principal research scientist in Harvard Chan School’s Department of Environmental Health.