Table 2 Characteristics of RA cases and matched controls: Caucasian matched pairs

Matching factors

   Age (years; mean ± SD)

57 ± 9

57 ± 9

43 ± 5

43 ± 5

   Postmenopausal (n [%])

263 (68%)

255 (66%)

14 (29%)

14 (29%)

   Current PMH use (n [%])^a

111 (36%)

101 (34%)

11 (69%)

12 (75%)

Other characteristics

   Ever cigarette smokers (n [%])

246 (63%)

220 (57%)

19 (39%)

22 (45%)

   Pack-years among smokers, mean (SD)

24 ± 17

24 ± 20

16 ± 9

11 ± 6

   Parous (n [%])

352 (91%)

367 (95%)

46 (94%)

42 (86%)

   Breastfed babies ≥ 12 months total, among parous (n [%])^a

44 (13%)

65 (18%)

18 (43%)

18 (45%)

   Age at menarche <12 years (n [%])

87 (22%)

77 (20%)

16 (33%)

15 (31%)

   Irregular menstrual cycle (n [%])

55 (14%)

49 (13%)

9 (18%)

11 (22%)

   Husband education > college graduate (n [%])

77 (20%)

77 (20%)

19 (39%)

9 (18%)

   Physical activity (hours/day mean ± SD)

2 ± 3

2 ± 5

2 ± 3

3 ± 3

   Alcohol intake (g/day; mean ± SD)

6 ± 10

6 ± 9

2 ± 1

2 ± 2

   Body mass index (kg/m²; mean ± SD)

25 ± 4

26 ± 5

27 ± 7

26 ± 5