Background and aim: Accumulation of evidence has raised concern regarding the harmful effect of air pollution on cognitive function, but results are diverging. We aimed to investigate the longitudinal association of long-term exposure to air pollutants and cognitive impairment and its further progression to dementia in older adults residing in an urban area.
Methods: Data were obtained from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Cognitive impairment, no dementia (CIND) was assessed by a comprehensive neuropsychological battery (scoring >= 1.5 standard deviations below age-specific means in >= 1 cognitive domain). We assessed long-term residential exposure to particulate matters (PM2.5 and PM10) and nitrogen oxides (NOx) with dispersion modeling. The association with CIND was estimated using Cox proportional hazards models with 3-year moving average air pollution exposure. We further estimated the effect of long-term air pollution exposure on the progression of CIND to dementia using Cox proportional hazards models.
Results: Among 1987 cognitively intact participants, 301 individuals developed CIND during the 12-year followup. A 1-mu g/m(3) increment in PM2.5 exposure was associated with a 75% increased risk of incident CIND (HR = 1.75, 95 %CI: 1.54, 1.99). Weaker associations were found for PM10 (HR for 1-mu g/m(3) = 1.08, 95 %CI: 1.03-1.14) and NOx (HR for 10 mu g/m(3) = 1.18, 95 %CI: 1.04-1.33). Among those with CIND at baseline (n = 607), 118 participants developed dementia during follow-up. Results also show that exposure to air pollution was a risk factor for the conversion from CIND to dementia (PM2.5: HR for 1-mu g/m(3) = 1.90, 95 %CI: 1.48-2.43; PM10 : HR for 1-mu g/m(3) = 1.14, 95 %CI: 1.03-1.26; and NOR: HR for 10 mu g/m(3) = 1.34, 95 %CI: 1.07-1.69).
Conclusion: We found evidence of an association between long-term exposure to ambient air pollutants and incidence of CIND. Of special interest is that air pollution also was a risk factor for the progression from CIND to dementia.