Characteristics of rheumatoid arthritis (RA) cases and matched controls in the Nurses’ Health Study (NHS; 1976–2002) and the Nurses’ Health Study II (NHSII; 1989–2003)
| Nurses’ Health Study (390 matched pairs) | Nurses’ Health Study II (49 matched pairs) | |||
| RA cases | Controls | RA cases | Controls | |
| Matching factors | ||||
| Age, mean (SD) | 56.7 (9.4) | 57.0 (9.3) | 43.1 (5.1) | 43.1 (5.1) |
| Postmenopausal (%) | 265 (68.0%) | 258 (66.2%) | 14 (28.6%) | 14 (28.6%) |
| Current PMH use (%)* | 114 (37.1%) | 106 (35.9%) | 11 (68.8%) | 12 (75.0%) |
| Other characteristics | ||||
| Ever cigarette smokers (%) | 246 (63.1%) | 223 (57.2%) | 19 (38.8%) | 22 (44.9%) |
| Pack-years among smokers, mean (SD) | 23.9 (16.7) | 24.1 (20.3) | 16.2 (9.1) | 10.8 (5.5) |
| Parous (%) | 355 (91.0%) | 368 (94.4%) | 46 (93.9%) | 42 (85.7%) |
| Breastfed babies ⩾12 months total (%)† | 46 (13.7%) | 65 (18.4%) | 18 (42.9%) | 18 (45.0%) |
| RA features | ||||
| Mean age at diagnosis, (SD) | 56.7 (9.4) | – | 43.1 (5.1) | – |
| Rheumatoid factor positive (%) | 224 (57.4%) | – | 27 (55.1%) | – |
| Anti-CCP‡ positive | 86 (47.8%) | – | 19 (46.3%) | – |
| Seropositive (%) | 238 (61.0%) | 32 (65.3%) | ||
| Rheumatoid nodules, (%) | 50 (12.8%) | – | 6 (12.2%) | – |
| Radiographic changes, (%) | 118 (30.3%) | – | 17 (34.7%) | – |
| Diagnosed by a member of ACR, (%) | 322 (84.1%) | – | 47 (95.9%) | – |
*Percentage is calculated among postmenopausal women or parous women, with unknown/missing group excluded; for the rest of the variables, percentage was calculated with missing category included. †Among parous women. ‡Anti-cyclic citrullinated peptide (CCP) antibodies assayed in subset of cases (NHS = 180, NHSII = 41) with stored blood samples at collected at different points with respect to RA onset, up to 12 years prior to onset or after diagnosis.
ACR, American College of Rheumatology; PMH, postmenopausal hormone.