PM_2.5 exposure and olfactory functions

Figures & data

Figure 1. Overview of the Betula project, showing the samples and test waves from which data were drawn for the different set of analyses.

Table 1. Characteristics and background variables for the study samples used in the different analyses.

			Long-term PM2.5
	Short -PM2.5		Odor identification		Odor detection
	Odor identification (n = 1088)	Odor detection (n = 1088)	Test score (n = 2521)	Rate of change (n = 1019)	Test score (n = 1051)	Rate of change (n = 511)
PM2.5 exposure, µg/m^3 (m, (sd))	4.56 (2.66)	4.6 (2.7)	6.7 (0.5)	6.7 (0.5)	5.4 (0.5)	5.4 (0.5)
Age at baseline (m, (sd))	63.0 (14.7)	62.1 (14.2)	63.5 (13.8)	60.4 (11.2)	62.2 (14.2)	63.2 (10.9)
Years of education (m, (sd))	-	-	10.5 (4.2)	11.4 (4.2)	12.6 (4.2)	12.8 (4.2)
Sex = Female (n (%))	585 (53.8)	556 (53.3)	1136 (54.1)	547 (53.7)	566 (54.0)	271 (53.0)
APOE-ε4 carrier (n (%))	-	-	582 (29.4)	309 (30.3)	247 (23.5)	151 (29.5)
Missing (n (%))			541 (21.5)		267 (25.4)
Current or former smoker (n (%))	-	-	1159 (46.1)	509 (50.0)	472 (44.9)	338 (46.7)

Table 2. Mean values and standard deviations for the outcome variables used in the different analyses.

	Odor identification	Odor detection
Score at T5^a (m, (sd))	6.7 (2.3), n = 1088	5.6 (3.1), n = 1088
Score at participant’s^b
1st test (m, (sd))	7.0 (2.3), n = 2521	5.6 (3.0), n = 1051
2nd test (m, (sd))	6.4 (2.2), n = 1055	5.1 (2.8), n = 511
3rd test (m, (sd))	6.6 (2.3), n = 740	-
4th test (m, (sd))	7.3 (2.3), n = 451	-
Difference between^c
2nd-1st test (m, (sd))	−1.1 (2.4), n = 1019	−0.5 (3.5), n = 511
3nd-1st test (m, (sd))	−1.2 (2.3), n = 730	-
4nd-1st test (m, (sd))	−0.7 (2.4), n = 451	-

a) Used in analyses of short-term exposure and olfactory outcomes. b) Used in analyses of long-term exposure and olfactory outcomes. c) Used in analyses of long-term exposure and rate of change in olfactory outcomes

Table 3. Estimated regression parameters (β) and 95% confidence intervals (95% CI) on odor identification and detection and rate of change of these scores over time. The fully adjusted model was adjusted for age, sex, education, APOE-ε4 status, and smoking habits. Rate of change is defined as the difference in test score from the participants' first test occasion. All models using rate of change as outcome variable were also adjusted for baseline performance (*p < 0.05, **p < 0.01, ***p < 0.001).

	ODOR IDENTIFICATION				ODOR DETECTION
	Test score		Rate of change		Test score		Rate of change
	β	95% CI	β	95% CI	β	95% CI	β	95% CI
Crude model
PM2,5	0.15*	0.01, 0.29	0.03	−0.23, 0.17	0.12	−0.20, 0.44	0.07	−0.40, 0.53
Age adjusted model
PM2,5	0.27***	0.13, 0.41	0.06	−0.12, 0.25	0.20	−0.10, 0.51	0.15	−0.30, 0.61
Age	−0.08***	−0.81, −0.70	−0.07***	−0.07, −0.06	−0.06***	−0.07, −0.48	−0.06***	−0.08, −0.03
Fully adjusted model
PM2,5	0.20**	0.06, 0.34	0.03	−0.15, 0.21	0.10	−0.22, 0.43	0.06	−0.40, 0.53
Age	−0.07***	−0.07, −0.06	−0.06***	−0.07, −0.05	−0.06***	−0.07, −0.04	−0.47***	−0.07, −0.22
Education	0.05***	0.03, 0.07	0.04*	0.01, 0.06	0.02	−0.02, 0.07	0.04	−0.25, 0.10
Sex = female	0.57***	0.43, 0.72	0.38***	0.18, 0.58	0.32	−0.01, 0.64	0.11	−0.36, 0.59
APOE-ε4 non-carrier	0.16*	0.00, 0.32	0.09	−0.12, 0.30	0.08	−0.27, 0.43	−0.27	−0.79, 0.45
Current/former smoker	0.09	−0.61, 0.23	0.07	−0.12, 0.27	−0.01	−0.33, 0.32	−0.22	−0.69, 0.26

Data availability statement

Data from the Betula project cannot be made publicly available due to ethical and legal restrictions. However, access to these original data is available upon request from the corresponding author (J.A.) and after approval by the Steering Group of the Betula project (https://www.umu.se/en/betula). Access to data by qualified investigators is subject to scientific and ethical review and must comply with the European Union General Data Protection Regulations (GDPR)/all relevant guidelines. The completion of a data transfer agreement (DTA) signed by an institutional official will be required.