Long-Term exposure to NO2 and Stroke Mortality in Portugal: an ecological study from 2001 to 2021

Abstract

Abstract Background Air pollution is an important contributing factor for many pathologies, including stroke. Nitrogen dioxide (NO2), an air pollutant, has been associated in multiple studies with strokes’ mortality. Aim This study aims, for the first time, to estimate the number of deaths by stroke due to long-term, ambient exposure to nitrogen dioxide in Portugal for the years 2001-2021. Methods An ecological study was considered, including data for NO2 outdoor concentration from Portugal. Mortality data by stroke was obtained divided in 5-year groups. It was also obtained life expectancy for each year to calculate the years of life lost (YLL). The hazard ratio (HR) was obtained from literature (1.009, CI 1.003-1.016). The population attributable fraction (PAF) of YLL by stroke due to ambient NO2 long-term exposure was calculated. Results The annual average NO2 concentration in Portugal decreased from its peak in 2001 of 29.4 to 12.2 µg/m3 in 2021. The YLL by stroke decreased from an estimated 57452 to 31204 from 2001 to 2021. The PAF of YLL by stroke due to ambient NO2 long-term exposure reached its peak in 2001, when an estimated 5.2% of all the YLL by stroke, corresponding to 3029 YLL, were due to NO2 exposure and a bottom in 2021, when 2.2%, corresponding to 682 YLL, where due NO2 exposure. Conclusions The policies and legislation implemented to curb down NO2 seem to have had an effect in Portugal. A reduction in NO2 emissions was achieved, having a significant impact on YLL by stroke in Portugal, suggesting that curbing the NO2 emissions down had a positive effect on mortality by stroke in Portugal. To further enhance our knowledge on the real impacts of NO2, further studies must be conducted to estimate the morbidity associated with NO2 on stroke as well as in other diseases. Key messages • Pollution by nitrogen dioxide decreased significantly from 2001 to 2021. • Around 20000 years of life were lost just in Portugal due to nitrogen dioxide between 2001 and 2021.