Effects of particulate air pollution on blood pressure in a highly exposed population in Beijing, China: a repeated-measure study

Table 1 Characteristics of the Study Participants

		Office Workers (n = 60)	Truck Drivers (n = 60)	p-value^a
Sex, n (%)
	Male	40 (66.67)	40 (66.67)
	Female	20 (33.33)	20 (33.33)	1.00
Age [Years], mean ± SD		30.27 ± 7.96	33.53 ± 5.65	0.004
Smoking, n (%)
	Never smoker	35 (58.33)	34 (56.67)
	Ex-smoker	2 (3.33)	2 (3.33)
	Actual smoker	23 (38.33)	24 (40)	1.00
Pack-years of smoking [kg/m ² ], mean ± SD ^b		2.87 ± 3.59	11.7 ± 11.2	<0.001
Cigarettes smoked during the study time ^c [cigarettes/day], mean ± SD		2.85 ± 5.21	6.39 ± 9.41	<0.001^c
BMI [kg/m ² ], mean ± SD		22.76 ± 3.38	24.27 ± 3.21	0.01
Tea consumption during the time of the study ^c , n (%)
	No	109 (90.83)	86 (71.67)
	Yes	11 (9.17)	34 (28.33)	0.003^c
Day of the week ^c , n (%)
	Monday	16 (13.33)	19 (15.83)
	Tuesday	18 (15)	13 (10.83)
	Wednesday	14 (11.67)	15 (12.5)
	Thursday	15 (12.5)	20 (16.67)
	Friday	17 (14.17)	19 (15.83)
	Saturday	18 (15)	16 (13.33)
	Sunday	22 (18.33)	18 (15)	0.88^c
Usual alcohol drinking, n (%)
	Yes	14 (23.33)	31 (51.67)
	No	46 (76.67)	29 (48.33)	0.002

^aP-values were calculated using Student's t-test and Fisher's exact test for continuous and categorical variables, respectively, except for the variables indicated at the footnote ^c below.
^bOnly current or former smokers.
^cCumulative of the two study days. Based on 240 total observations (120 study days for office workers and 120 study days for truck drivers). P-values were obtained from mixed-effect regression models.

ISSN: 1476-069X