Short-term association between environmental factors and hospital admissions due to dementia in Madrid

Background: Spain has one of the highest proportions of dementia in the world among the population aged 60 years or over. Recent studies link various environmental factors to neurocognitive-type diseases. This study sought to analyse whether urban risk factors such as traffic noise, pollutants and heat waves might have a short-term impact on exacerbation of symptoms of dementia, leading to emergency hospital admission. Material and methods: We conducted a longitudinal ecological time-series study, with the dependent variable being the number of daily dementia-related emergency (DDE) hospital admissions to Madrid municipal hospitals (ICD-10 codes 290.0-290.2, 290.4-290.9, 294.1-294) from 01 to 01-2001 to 31-12-2009, as obtained from the Hospital Morbidity Survey (National Statistics Institute). The measures used were as follows: for noise pollution, Leqd, equivalent diurnal noise level (from 8 to 22 h), and Leqn, equivalent nocturnal noise level (from 22 to 8 h) in dB(A); for chemical pollution, mean daily NO2, PM2.5, PM1 as provided by the Madrid Municipal Air Quality Monitoring Grid; and lastly, maximum daily temperature (degrees C), as supplied by the State Meteorological Agency. Scatterplot diagrams were plotted to assess the type of functional relationship existing between the main variable of analysis and the environmental variables. The lags of the environmental variables were calculated to analyse the timing of the effect. Poisson regression models were fitted, controlling for trends and seasonalities, to quantify relative risk (RR). Results: During the study period, there were 1175 DDE hospital admissions. These admissions displayed a linear functional relationship without a threshold in the case of Leqd. The RR of DDE admissions was 1.15 (1.11-1.20) for an increase of 1 dB in Leqd, with impact at lag 0. In the case of maximum daily temperature, there was a threshold temperature of 34 degrees C, with an increase of 1 degrees C over this threshold posing an RR of 1.19 (1.09-1.30) at lag 1. The only pollutant to show an association with DDE hospital admissions was 03 at lag 5, with an RR of 1.09 (1.04-1.15) for an increase of 10 mu g/m(3) Conclusions: Diurnal traffic noise, heat waves and tropospheric ozone may exacerbate the symptoms of dementia to the point of requiring emergency admission to hospital. Lowering exposure levels to these environmental factors could reduce dementia-related admissions in Madrid.