Table 1.
Baseline characteristics of study participants in the UK Biobank
| Characteristics | Total participants (n=223 526) |
No incident RA (n=220 213) | Incident RA (n=3313) | P value |
| Age at baseline, years (mean±SD) | 56.2±8.02 | 56.2±8.02 | 59.3±7.20 | <0.001 |
| Townsend deprivation index (mean±SD) | -1.41±2.98 | -1.42±2.98 | -0.94±3.15 | <0.001 |
| Ethnicity, n (%) | <0.001 | |||
| White | 211 513 (94.6) | 208 425 (94.6) | 3088 (93.2) | |
| Other | 12 013 (5.4) | 11 788 (5.4) | 225 (6.8) | |
| Smoking status, n (%) | ||||
| Never smoker | 134 016 (60.0) | 132 305 (60.0) | 1711 (51.7) | <0.001 |
| Former smoker | 70 741 (31.6) | 69 514 (31.6) | 1227 (37.0) | |
| Current smoker | 18 769 (8.4) | 18 394 (8.4) | 375 (11.3) | |
| Alcohol drinker status, n (%) | <0.001 | |||
| Never drinker | 12 197 (5.5) | 11 901 (5.4) | 292 (8.8) | |
| Former drinker | 7557 (3.4) | 7348 (3.3) | 209 (6.3) | |
| Current drinker | 203 776 (91.1) | 200 964 (91.3) | 2812 (84.9) | |
| BMI, kg/m2 (mean±SD) | 26.9±5.01 | 26.8±4.99 | 28.4±5.70 | <0.001 |
| Physical activity, MET-min/week, n (%) | <0.001 | |||
| Low (<600) | 44 581 (19.9) | 43 794 (19.9) | 787 (23.8) | |
| Moderate (≥600, <3000) | 116 859 (52.3) | 115 272 (52.3) | 1587 (47.9) | |
| High (≥3000) | 62 086 (27.8) | 61 147 (27.8) | 939 (28.3) | |
| Vitamin D supplement, n (%) | 0.036 | |||
| No | 175 222 (78.4) | 172 575 (78.4) | 2647 (79.9) | |
| Yes | 48 304 (21.6) | 47 638 (21.6) | 666 (20.1) | |
| Fracture history, n (%) | <0.001 | |||
| No | 200 847 (89.9) | 197 979 (89.9) | 2868 (86.6) | |
| Yes | 22 679 (10.1) | 22 234 (10.1) | 445 (13.4) | |
| Diabetes, n (%) | <0.001 | |||
| No | 215 709 (96.5) | 212 614 (96.5) | 3095 (93.4) | |
| Yes | 7817 (3.5) | 7659 (3.5) | 218 (6.6) | |
| Blood pressure | ||||
| SBP, mm Hg (mean±SD) | 137.0±20.25 | 137.0±20.25 | 140.0±19.85 | <0.001 |
| DBP, mm Hg (mean±SD) | 80.0±10.54 | 80.0±10.54 | 81.0±10.42 | 0.006 |
| Rheumatoid factor status, n (%) | <0.001 | |||
| RF-negative | 202 037 (90.4) | 199 580 (90.6) | 2457 (74.2) | |
| RF-positive Missing |
7060 (3.2) 14 429 (6.4) |
6589 (3.0) 14 044 (6.4) |
471 (14.2) 385 (11.6) |
|
| Age at menarche, years (mean±SD) | 123.0±1.62 | 13.0±1.61 | 13.0±1.74 | 0.823 |
| Ever been pregnant, n (%) | <0.001 | |||
| No | 33 204 (14.8) | 32 787 (14.9) | 417 (12.6) | |
| Yes | 189 479 (84.8) | 186 592 (84.7) | 2887 (87.1) | |
| Missing | 843 (0.4) | 834 (0.4) | 9 (0.3) | |
| Number of children, n (%) | <0.001 | |||
| None | 42 427 (19.0) | 41 894 (19.0) | 533 (16.1) | |
| 1 | 29 814 (13.3) | 29 353 (13.3) | 461 (13.9) | |
| 2 | 98 159 (43.9) | 96 762 (43.9) | 1397 (42.2) | |
| 3 | 39 249 (17.6) | 38 635 (17.6) | 614 (18.5) | |
| ≥4 | 13 732 (6.1) | 13 426 (6.1) | 306 (9.2) | |
| Missing | 145 (0.1) | 143 (0.1) | 2 (0.1) | |
| Menopause, n (%) | <0.001 | |||
| No | 62 312 (27.9) | 61 831 (28.1) | 481 (14.5) | |
| Yes | 160 991 (72.0) | 158 164 (71.8) | 2827 (85.3) | |
| Missing | 223 (0.1) | 218 (0.1) | 5 (0.2) | |
| Age at menopause, years (mean±SD) | 50.0±5.08 | 50.0±5.07 | 50.0±5.95 | <0.001 |
| Reproductive years, years (mean±SD) | 37.0±5.32 | 37.0±5.30 | 36.0±6.09 | <0.001 |
| History of hysterectomy, n (%) | <0.001 | |||
| No | 182 785 (81.8) | 180 447 (81.9) | 2338 (70.5) | |
| Yes | 15 896 (7.1) | 15 500 (7.1) | 396 (12.0) | |
| Missing | 24 845 (11.1) | 24 266 (11.0) | 579 (17.5) | |
| History of oophorectomy, n (%) | <0.001 | |||
| No | 203 279 (90.9) | 200 418 (91.0) | 2861 (86.4) | |
| Yes | 17 368 (7.8) | 17 003 (7.7) | 365 (11.0) | |
| Missing | 2879 (1.3) | 2792 (1.3) | 87 (2.6) | |
| Ever used oral contraceptive pills, n (%) | <0.001 | |||
| No | 40 867 (18.3) | 40 100 (18.2) | 767 (23.2) | |
| Yes | 182 152 (81.5) | 179 616 (81.6) | 2536 (76.5) | |
| Missing | 507 (0.2) | 497 (0.2) | 10 (0.3) | |
| Duration of oral contraceptive pill use, years (mean±SD) | 10.4±7.68 | 10.4±7.68 | 9.8±7.65 | <0.001 |
| Ever used HRT, n (%) | <0.001 | |||
| No | 139 012 (62.2) | 137 479 (62.4) | 1533 (46.3) | |
| Yes | 83 911 (37.5) | 82 145 (37.3) | 1766 (53.3) | |
| Missing | 603 (0.3) | 589 (0.3) | 14 (0.4) | |
| Duration of HRT use, years (mean±SD) | 6.3±5.28 | 6.3±5.26 | 7.1±5.88 | <0.001 |
BMI, body mass index; DBP, diastolic blood pressure; HRT, hormone replacement therapy; MET, metabolic equivalents; RA, rheumatoid arthritis; RF, rheumatoid factor; SBP, systolic blood pressure.