Table 1 Age-standardized characteristics by calendar-year-adjusted PM_2.5 quintiles in premenopausal (n = 1624) and postmenopausal (n = 1634) participants

Age at mammogram^b

45.6 ± 4.2

45.6 ± 4.3

60.0 ± 7.4

59.7 ± 7.6

NHSII cohort (%)

76

78

19

24

BMI at mammogram (kg/m²)

25.1 ± 5.6

25.8 ± 5.5

26.1 ± 5.0

26.5 ± 5.6

Presence of biopsy-confirmed benign breast disease (%)

18.8

17.8

23.4

21.8

Current use of hormonal therapy (%)

2.7

2.3

52.2

47.3

 Nulliparous

16.3

16.5

9.8

9.8

 1–4 children before age 25

29.0

29.3

36.5

38.2

 1–4 children between age 25 and 30

33.8

34.4

31.9

29.5

 1–4 children after age 30

17.7

17.0

8.6

9.8

 5+ children

2.6

1.9

12.6

11.7

 Missing

0.6

0.9

0.5

1.0

  < 19.0 kg/m²

16.0

17.8

10.6

13.3

 19.0–24.9 kg/m²

72.2

70.7

75.6

72.9

 25–29.9 kg/m²

7.4

8.5

9.4

8.1

 30+ kg/m²

1.9

1.7

0.9

1.9

 Missing

2.5

1.3

3.5

3.8

Family history of breast cancer (%)

10.7

8.5

13.0

11.0

Age at menarche (years)

12.4 ± 1.4

12.4 ± 1.4

12.4 ± 1.3

12.6 ± 1.5

 Never breastfed

15.0

21.9

35.8

41.5

 Yes‚ breastfed > 1 month

82.5

75.1

62.8

57.0

 Missing

2.5

3.1

1.5

1.3

 Not on oral contraceptives

94.4

93.4

–

–

 Current < 5 years

2.6

1.5

–

–

 Current 5 + years

2.7

4.9

–

–

 Missing

0.3

0.3

–

–

Alcohol consumption (g/day)

5.3 ± 8.4

3.8 ± 6.3

5.6 ± 9.1

4.8 ± 8.1

Physical activity (MET hours/week)

22.2 ± 29.6

17.5 ± 19.2

17.6 ± 17.3

19.4 ± 26.3

White (%)

99.4

97.5

98.6

97.7

 Northeast

27.8

27.4

28.0

33.4

 Midwest

13.8

40.5

6.5

34.8

 West

39.4

16.5

33.8

20.6

 South

18.9

15.6

31.7

11.2

Distance from residential address to A1–A3 roadways (meters)

313.8 ± 185.9

231.1 ± 169.6

299.0 ± 187.5

220.2 ± 168.1