Long-term exposure to air pollution and road traffic noise and incidence of dementia in the Danish Nurse Cohort

Abstract

Introduction: We examined the association of long-term exposure to air pollution and road traffic noise with dementia incidence in the Danish Nurse Cohort.

Methods: Female nurses were followed for dementia incidence (hospital contact or medication prescription) from 1993/1999 to 2020. Air pollution and road traffic noise levels were estimated at nurses' residences, and their associations with dementia were examined using Cox regression models.

Results: Of 25,233 nurses 1409 developed dementia. Particulate matter with a diameter of ≤2.5 µm (PM_2.5) was associated with dementia incidence, after adjusting for lifestyle, socioeconomic status, and road traffic noise (hazard ratio [95% confidence interval] 1.35 [1.15-1.59] per interquartile range of 2.6 µg/m³). There was no association of PM2.5 with dementia in physically active nurses. Association with road traffic noise diminished after adjusting for PM₂.₅ (1.02 [0.93-1.11] per 7.6 dB).

Discussion: Long-term exposure to air pollution increases risk of dementia, and physical activity may moderate this risk.

Highlights: Long-term exposure to air pollution was associated with increased risk of dementia among female nurses from the Danish Nurse Cohort. Association of air pollution with dementia was independent of road traffic noise. Association of road traffic noise with dementia diminished after adjusting for air pollution. Physical activity moderated adverse effects of air pollution on dementia.

Keywords: Europe; air pollution; cohort studies; dementia; incidence; noise transportation; nurses; physical activity; women.

FIGURE 1

Levels of air pollution and road traffic noise levels of nurses from the Danish Nurse Cohort at the cohort baseline aggregated at the municipality level. BC, black carbon; L_den, day–evening–night road traffic noise levels; NO₂, nitrogen dioxide; O₃, ozone; PM₂․₅, particulate matter with a diameter of ≤2.5 µm; PM₁₀, particulate matter with a diameter of ≤10 µm.

FIGURE 2

Exposure‐response functions of the associations between air pollution and road traffic noise and incidence of dementia in the Danish Nurse Cohort (n = 24,848). Exposure‐response functions were modeled using penalized spline. Reference value is the median of exposure levels. BC, black carbon; L_den, day–evening–night road traffic noise levels; NO₂, nitrogen dioxide; O₃, ozone; PM₂․₅, particulate matter with a diameter of ≤2.5 µm; PM₁₀, particulate matter with a diameter of ≤10 µm.

FIGURE 3

Effect modification analysis of associations between (A) PM₂․₅ and (B) NO₂ and the incidence of dementia when considering interaction with characteristics of the nurses from the Danish Nurse Cohort at the cohort baseline in 1993 or 1999 (n = 24,848). Interaction was added as a multipliticative term in models adjusted for L_den (Models 4). Significance of an interaction term in the model was tested using the likelihood ratio test, and the p‐value reported in the figure. Interaction term estimates are provided in Table S8. HR values per each IQR of each air pollutant or noise are as follows: PM_2.5 = 2.96; PM₁₀ = 3.35; black carbon = 0.32; NO₂ = 7.46; O₃ = 6.06; L_den = 9.5. BMI, body mass index; CI, confidence interval; CVD, cardiovascular disease; HR, hazard ratio; PM₂․₅, particulate matter with a diameter of ≤2.5 µm; PM₁₀, particulate matter with a diameter of ≤10 µm