Table 1

Characteristics and baseline exposure information on RA cases and matched controls

Cases n=136Controls n=544
Characteristics
 Mean age at RA diagnosis (SD)63.3 (8.3)NA
 Mean age at screening (SD; range)57.9 (7.3; 45–72)58.0 (7.3; 45–73)
 Anti-CCP positive at diagnosis, %56.0NA
 RF positive at diagnosis, %68.4NA
Baseline exposure information
 Reproduction-related factors
  Menopause-related factors
   Mean age at menopause (SD; range)47.9 (6.0; 26–57)49.2 (4.5; 19–59)
   Early menopause, ≤45 years, n (%)26 (19.1)62 (11.4)
   Normal to late menopause, n (%)103 (75.7)444 (81.6)
  Menarche-related factors
   Mean age at menarche (SD; range)13.7 (1.44; 10–18)13.5 (1.5; 10–20)
   Early menarche, <12 years, n (%)3 (2.2)46 (8.5)
   Normal to late menarche, n (%)125 (97.7)465 (91.0)
  Other factors
   No of fertile years, mean (SD)*34.2 (6.4)35.6 (4.7)
   Given birth to ≥1 child, n (%)106 (77.9)445 (81.8)
   Breast-fed 0 months, n (%)43 (31.6)137 (25.2)
   Breast-fed 1–12 months, n (%)74 (54.4)297 (54.6)
   Brest-fed >13 months, n (%)19 (14.0)110 (20.2)
 Self-reported stress–related factors
   Lack of physical and mental wellbeing, n (%)39 (30.0)161 (31.3)
   Problems falling a sleep at night, n (%)32 (23.5)105 (19.3)
   Problems waking up in the night, n (%)32 (23.5)136 (25)
   Problems waking up early, n (%)13 (9.6)85 (15.6)
  • * Data on 487 out of 680.

  • 26/46 tested.

  • 91/133 tested.

  • CCP, cyclic citrullinated peptide; NA , not applicable; RA, rheumatoid arthritis; RF, rheumatoid factor.