Interactive effects of air pollutants and temperature on incidence of dementia: a prospective cohort study

Abstract

Mounting evidence has linked air pollution with dementia and temperature modifies the association of air pollution with other disease. However, their interactions on dementia are unclear. We used a prospective cohort study (the UK Biobank) included 498 660 adults without cognitive impairment or dementia at baseline and followed up for 11.50 years (5734 907 person-years). We applied Cox proportional hazards regression with time-varying exposures to examine the effects of air pollutants [particulate matter (PM_2.5, PM₁₀), nitrogen oxides (NO₂, NO_X) and sulphur dioxide (SO₂)], the mean and variability of seasonal temperature, and their interactions on dementia. During the follow-up time, we ascertained 4119 cases of dementia. We observed a higher hazard of incident dementia for 1 μg m⁻³ increase in SO₂ (hazard ratio [HR] = 1.11; 95% confidence interval [CI]: 1.08, 1.14), NO₂ (HR [95% CI] = 1.02 [1.01, 1.02]), NO_X (HR [95% CI] = 1.01 [1.00, 1.01]), PM_2.5 (HR [95% CI] = 1.03 [1.02, 1.05]), and PM₁₀ (HR HR [95% CI] = 1.02 [1.00, 1.03]). A lower risk of dementia in summertime temperature variability (HR for 1 °C increment above 1.27 °C = 0.61; 95% CI: 0.51, 0.72) was found. We observed a nonlinear relationship between higher risk of dementia and higher summer temperatures, and strong U-shaped relation of both wintertime temperature and wintertime temperature variability with dementia. We found the significantly synergistic effect between SO₂ and summertime temperature (p < 0.001), the antagonistic effect between NO₂ (p = 0.043), NO_X (p = 0.026) and summertime temperature variability. Participants in a lower social economic position dominated susceptibility in temperature-air pollution interaction on dementia. In conclusion, some evidence of interactive effects between summer temperature and air pollutants was found, but no consistent interaction could be identified during the winter. Our study added weight to the evidence of air pollutants, temperature and their interaction on the onset of dementia.