Muye Ru, Drew Shindell, et al, Duke University, upcoming
Background: PM2.5 damages human health and causes economic costs via a variety of pathways. Previous health impacts studies, including the latest Global Burden of Disease, have linked PM2.5 exposure with five diseases. However, recent epidemiological evidence from cohort studies has suggested an additional linkage between PM2.5 exposure and dementia, whose impacts on the broader population have not been studied.
Method: The researchers first perform a meta-analysis incorporating available results: two studies for ambient air pollution, two for second hand smoking, and seven for active smoking. Relative risk and the corresponding PM2.5 concentrations are extracted to build an integrated exposure-response curve. We test different models and select the one that best fits the data. The researchers then calculated grid-level relative risk and attributable fractions of dementia incidence using the integrated exposure-response model and global 0.5° by 0.5° gridded annual surface PM2.5 concentrations. Subsequently, country-level annual dementia incidence is calculated as the sum-product of baseline incidence, attributable fractions, and population. Attributable deaths are estimated by modeling the relationship between deaths and incidence as a function of age for each country. Finally, we calculate years lost due to disability (YLD) as the product of incidence, disability weight, and average years of dementia before death, and years of life lost (YLL) as the sum-product of deaths and standard life expectancy at age of death. The sum of YLD and YLL is disability-adjusted life years (DALY), the lost years of “healthy” life.
Results: As the underlying epidemiology and biological mechanism are not yet as well characterized as other PM2.5 impacts, these results are indicative. We find that globally, 650,000 new cases of dementia and 108,000 dementia deaths are attributable to PM2.5 exposure in 2015, leading to 1.02 million disability-adjusted life years (DALY), the lost years of “healthy” life. The spatial distributions of both incidence and deaths are very inhomogeneous. The ratio between YLD and YLL within DALY varies across countries from 0.5 to 4.
Ambient PM2.5 pollution causes about 5% of all deaths and 4% of DALY from all dementia and Alzheimer’s disease. This would induce US$38 billion economic cost in a single year, which shows an annual growth rate of 16%.