Table 1.
Characteristics of included studies on the association between air pollution and the risk of cognitive impairment*
| Author, (year) [Ref.] | Country | Age (year), Sex | Follow-up years | Sample size (cases) | Exposure | Exposure measurement | Outcome | Source of outcome | RR (95% CI) | Adjustments |
|---|---|---|---|---|---|---|---|---|---|---|
| Carey (2018) [17] |
Britain |
50-79, Both |
9 |
130 978 (2181) |
PM2.5, NO2, O3 |
Dispersion mode |
Dementia |
Population based |
PM2.5, original value (Per IQR = 0.95μg/m3): 1.06 (1.02, 1.12); equivalent value (Per 5 μg/m3): 1.36 (1.11, 1.82). |
Age, sex, ethnicity, smoking, body mass index, index of multiple deprivation comorbidity (ischemic heart disease, stroke, heart failure). |
| PM2.5 (traffic), original value (Per IQR = 0.58μg/m3): 1.08 (1.01, 1.16); equivalent value (Per 5 μg/m3): 1.94 (1.09, 3.59). | ||||||||||
| NO2, original value (Per IQR = 7.47μg/m3): 1.16 (1.05, 1.27); equivalent value (Per 5 ppb): 1.21 (1.06, 1.35). | ||||||||||
| O3, original value (Per IQR = 5.56μg/m3): 0.85 (0.76, 0.94); equivalent value (Per 5 ppb): 0.75 (0.62, 0.90). | ||||||||||
| Oudin (2016) [26] |
Sweden |
55-85, Both |
18 |
1806 (302) |
NOx |
LUR |
Dementia |
Population based |
Original value (Per 10 μg/m3): 1.05 (0.98, 1.12); equivalent value (Per 5 ppb): 1.05 (0.98, 1.11). |
Baseline age, sex, education, physical activity, smoking, body mass index, waist–hip ratio, alcohol, ApoE4, baseline medical history of diabetes, stroke and hypertension. |
| Oudin (2018) [24] |
Sweden |
55-85, Both |
18 |
1806 (302) |
PM2.5 |
Dispersion mode |
Dementia |
Population based |
Wood burning, original value (Per 1μg/m3): 1.55 (1.00, 2.41); equivalent value (Per 5 μg/m3): 8.95 (1.00, 81.30). |
Age, sex, PM2.5 from traffic exhaust, PM2.5 from residential wood burning, physical activity, smoking, body mass index, alcohol and waist-hip-ratio. |
| Traffic exhaust, original value (Per 1μg/m3): 1.14 (0.59, 2.23); equivalent value (Per 5 μg/m3): 1.93 (0.07, 55.15). | ||||||||||
| Chen (2017) [18] |
Canada |
55-85, Both |
13 |
2 066 639 (257 816) |
PM2.5, NO2, O3 |
LUR |
Dementia |
Population based |
PM2.5, original value (Per IQR = 4.8μg/m3): 1.04 (1.03, 1.05); equivalent value (Per 5 μg/m3): 1.04 (1.03, 1.05). |
Age, sex, history of diabetes, hypertension, coronary heart disease, stroke, congestive heart failure, arrhythmia, traumatic brain injury, income quintile, urban residency, north/south indicator, census division-level unemployment rate, education and recent immigrants. |
| NO2, original value (Per IQR = 14.2 ppb): 1.10 (1.08, 1.12); equivalent value (Per 5 ppb): 1.034 (1.027,1.041). | ||||||||||
| O3, original value (Per IQR = 6.3 ppb): 0.98 (0.96, 1.00); equivalent value (Per 5 ppb): 0.98 (0.97, 1.00). | ||||||||||
| Cerza (2019) [20] |
Italy |
65-100, Both |
13 |
350 844 (21 548) |
PM2.5, NO2, NOx O3 |
LUR and chemical transport model |
Dementia |
Hospital based |
PM2.5, original value (Per 5 μg/m3): 0.99 (0.96, 1.02). |
Age, education, place of birth, marital status, area-based socioeconomic position with baseline hazard function stratified by sex. |
| NO2, original value (Per 10 μg/m3): 0.97 (0.96, 0.99); equivalent value (Per 5 ppb): 0.97 (0.96, 0.99). | ||||||||||
| NOx, original value (Per 20 μg/m3): 1.01 (1.00, 1.02); equivalent value (Per 5 ppb): 1.005 (1.000, 1.009). | ||||||||||
| O3, original value (Per 10 μg/m3):1.06 (1.03, 1.08); equivalent value (Per 5 ppb): 1.06 (1.03, 1.08). | ||||||||||
| Kioumourtzoglou (2016) [19] |
America |
75, Both |
12 |
9 817 806 (230 463) |
PM2.5 |
The US Environmental Protection Agency’s (EPA) Air Quality System (AQS) database |
Dementia |
Hospital based |
Original value (Per 5 μg/m3): 1.46 (1.29, 1.66). |
Age, sex, race, individual socioeconomic status and for any prior cardiopulmonary admission and severity of disease. |
| Ilango (2019) [21] |
Canada |
60, Both |
18 |
34 391 (2559) |
PM2.5, NO2 |
LUR |
Dementia |
Population based |
PM2.5, original value (Per 10 μg/m3): 1.29 (0.99, 1.64); equivalent value (Per 5 μg/m3): 1.14 (0.99, 1.28). |
Age, sex, education, marital status, income quintile, smoking status, body mass index, physical activity, rural residence and northern region; area level: recent immigrants, unemployment and education. |
| NO2, original value (Per 5 ppb): 1.10 (0.99, 1.19). | ||||||||||
| Yu (2016) [25] |
Canada |
≥65, Both |
14 |
5249 (1346) |
PM2.5, NO2 |
Satellite imaging and LUR |
Dementia |
Population based |
PM2.5, original value (Per 10 μg/m3): 1.14 (0.93, 1.40); equivalent value (Per 5 μg/m3): 1.07 (0.96, 1.18). |
Age, sex, vitamin use, non-steroidal anti-inflammatory drugs, exercise, hypertension, and obesity. |
| NO2, original value (Per 5 ppb): 0.98 (0.93, 1.03). | ||||||||||
| Jung (2015) [22] |
China |
≥65, Both |
10 |
95 690 (1399) |
PM2.5, O3 |
Monitoring stations |
Alzheimer disease |
Population based |
PM2.5, original value (Per 13.21μg/m3): 1.03 (0.95, 1.11); equivalent value (Per 5 μg/m3): 1.01 (0.98, 1.04). |
Age, sex, income, diabetes mellitus, hypertensive disease, myocardial infarction, stroke, asthma and chronic obstructive pulmonary disease. |
| O3, original value (Per 9.63 ppb): 1.06 (1.00, 1.12); equivalent value (Per 5 ppb): 1.03 (1.00,1.06). | ||||||||||
| Loop (2013) [23] | America | 64, Men: 45% | 4 | 20 150 (1633) | PM2.5 | Ground-level and Earth-orbiting satellite measurements | Cognitive impairment | Population based | Original value (Per 10 μg/m3): 0.98 (0.72, 1.34); equivalent value (Per 5 μg/m3): 0.99 (0.85, 1.16). | Age, race, region, education, body mass index, income, PM2.5, length of follow up, the potential confounders temperature,season,incident stroke, smoking status, alcohol use, exercis and comorbidities (presence of depressive symptoms, diabetes,dyslipidemia, hypertension). |
RR – relative risk, PM2.5 – particulate matter ≤2.5 μm, NO2 – nitrogen dioxide NOx – nitrogen oxide, O3 – ozone; LUR – land-use regression model; Equivalent value, RR standardized = RRuincrement unit (eg, 5)/u is the equation for converting the original value to the equivalent value. RR standardized denotes equivalent value, RRu denotes original value, u denotes the increment of PM2.5, NO2, NOx, O3 concentration used in the original study, ppb - parts per billion
*Conversion factors: NO2/NOx: 1 ppb = 1.88 μg/m3; O3, 1 ppb = 1.96 μg/m3.