Assessing intergenerational health equity in the mortality impacts of acute and chronic air pollution exposure

Although mortality effects of short- and long-term air pollution exposure have been widely studied, temporal and intergenerational variations in vulnerability across age and cause-specific groups remain unclear.

We analyzed over 3.2 million individual death records from the ten most populated Japanese cities (1977-2015), constructing 5-year birth cohorts for middle-aged (40-64 years) and elder adults (65-89 years). Using a space-time-stratified case-crossover design for acute effects and an adapted difference-in-difference approach for chronic effects, we estimated cause-specific mortality risks per 10 unit increase in suspended particulate matter (SPM), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and photochemical oxidant (O_x). Intergenerational trends were assessed using weighted linear regression of log-transformed relative risks (RRs) on birth cohort.

SPM, NO₂, and SO₂ declined across cohorts, while O_x exhibited a gradual increase. We found higher short-term SPM-related mortality risks among middle-aged and elder adults born in more recent generations (all-cause mortality, middle-aged adults: RR_1931-1935 = 1.0011, 95% CI: 0.9985-1.0036 to RR_1951-1955 = 1.0097, 95% CI: 1.0047-1.0147; elder adults: RR_1906-1910 = 1.0025, 95% CI: 1.0008-1.0042 to RR_1926-1930 = 1.0055, 95% CI: 1.0034-1.0076). Middle-aged adults from younger generations were more sensitive to both acute and chronic NO₂ effects on all-cause and non-external mortality, whereas elder adults born in younger generations showed increased susceptibility to short-term and long-term O_x-related mortality for respiratory and circulatory causes, respectively. We also observed intergenerational increases in the acute effects of SO₂ on mortality among elder adults. Chronic effects showed cohort-specific variations, whereas acute effects were generally consistent.

Our cohort-based analysis provides the first direct evidence of intergenerational differences in both acute and chronic mortality effects of multiple air pollutants. These findings highlight intergenerational inequities in susceptibility to air pollution and the importance of considering such differences in future health impact assessments.