Table 2.
Hazard ratios (HR) and 95% confidence intervals (CI) for association between reproductive factors and risk of seropositive rheumatoid arthritis among postmenopausal women.
| Case no. | Duration (person-years) | IR per 100 000 person-years | HR (95% CI) | |||
|---|---|---|---|---|---|---|
| Model 1 (univariate) | Model 2 (multivariablea) | Model 3 (multivariableb) | ||||
| Age at menarche | ||||||
| ≤ 15 | 1836 | 3,486,901.2 | 52.7 | 1 (ref.) | 1 (ref.) | |
| 16 | 1302 | 2,371,367.7 | 54.9 | 1.04 (0.97–1.12) | 1.07 (0.99–1.15) | |
| 17 | 1237 | 2,217,704.0 | 55.8 | 1.06 (0.99–1.14) | 1.10 (1.02–1.18) | |
| ≥ 18 | 1681 | 3,105,263.2 | 54.1 | 1.03 (0.96–1.10) | 1.07 (1.00–1.15) | |
| Age at menopause | ||||||
| < 40 | 106 | 188,808.6 | 56.1 | 1 (ref.) | 1 (ref.) | |
| 40–44 | 372 | 633,034.4 | 58.8 | 1.05 (0.84–1.30) | 1.04 (0.84–1.29) | |
| 45–49 | 1657 | 3,040,776.6 | 54.5 | 0.97 (0.80–1.18) | 0.96 (0.79–1.16) | |
| 50–54 | 3270 | 6,125,361.4 | 53.4 | 0.95 (0.78–1.15) | 0.95 (0.79–1.16) | |
| ≥ 55 | 651 | 1,193,255.0 | 54.6 | 0.97 (0.79–1.19) | 1.01 (0.82–1.24) | |
| Reproductive period (years) | ||||||
| < 30 | 848 | 1,523,258.2 | 55.7 | 1 (ref.) | 1 (ref.) | |
| 30–34 | 2549 | 4,667,110.4 | 54.6 | 0.98 (0.91–1.06) | 0.98 (0.90–1.05) | |
| 35–39 | 2292 | 4,275,185.6 | 53.6 | 0.96 (0.89–1.04) | 0.96 (0.89–1.04) | |
| ≥ 40 | 367 | 715,681.9 | 51.3 | 0.92 (0.82–1.04) | 0.95 (0.84–1.07) | |
| Parity | ||||||
| Nulliparous | 176 | 276,955.1 | 63.5 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| 1 child | 377 | 682,989.3 | 55.2 | 0.87 (0.72–1.04) | 0.90 (0.74–1.08) | 0.89 (0.74–1.08) |
| ≥ 2 children | 5503 | 10,221,291.7 | 53.8 | 0.85 (0.73–0.99) | 0.92 (0.78–1.09) | 0.92 (0.78–1.09) |
| Duration of breastfeeding | ||||||
| Never | 453 | 743,663.5 | 60.9 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| < 0.5 years | 381 | 740,618.8 | 51.4 | 0.84 (0.74–0.97) | 0.86 (0.75–0.99) | 0.86 (0.74–0.99) |
| 0.5 to < 1 years | 1089 | 1,960,413.0 | 55.6 | 0.91 (0.82–1.02) | 0.95 (0.85–1.08) | 0.96 (0.85–1.08) |
| ≥ 1 years | 4133 | 7,736,540.7 | 53.4 | 0.88 (0.80–0.97) | 0.95 (0.85–1.06) | 0.95 (0.85–1.07) |
| Oral contraceptive use | ||||||
| Never used | 4843 | 8,926,291.4 | 54.3 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| < 1 years | 572 | 1,020,167.2 | 56.1 | 1.03 (0.95–1.13) | 1.03 (0.94–1.12) | 1.03 (0.94–1.12) |
| ≥ 1 years | 344 | 681,743.3 | 50.5 | 0.93 (0.83–1.04) | 0.94 (0.84–1.04) | 0.94 (0.84–1.05) |
| Unknown | 297 | 553,034.2 | 53.7 | 0.99 (0.88–1.11) | 0.99 (0.87–1.12) | 0.99 (0.87–1.12) |
| Hormone therapy | ||||||
| Never used | 4761 | 9,023,919.2 | 52.8 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| < 2 years | 612 | 1,025,567.6 | 59.7 | 1.13 (1.04–1.23) | 1.11 (1.01–1.20) | 1.11 (1.02–1.20) |
| 2 to < 5 years | 259 | 421,442.2 | 61.5 | 1.16 (1.03–1.32) | 1.14 (1.01–1.30) | 1.14 (1.01–1.30) |
| ≥ 5 years | 214 | 322,718.2 | 66.3 | 1.26 (1.10–1.44) | 1.25 (1.09–1.44) | 1.25 (1.09–1.44) |
| Unknown | 210 | 387,588.9 | 54.2 | 1.03 (0.89–1.18) | 1.04 (0.89–1.20) | 1.04 (0.89–1.20) |
| Smoking | ||||||
| Never smoker | 5786 | 10,766,679.6 | 53.7 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| Former smoker | 75 | 117,707.9 | 63.7 | 1.19 (0.94–1.49) | 1.24 (0.98–1.55) | 1.23 (0.98–1.55) |
| Current smoker | 195 | 296,848.6 | 65.7 | 1.22 (1.06–1.41) | 1.26 (1.09–1.46) | 1.26 (1.09–1.46) |
| Alcohol consumption | ||||||
| Non | 5392 | 9,763,085.0 | 55.2 | 1(ref.) | 1(ref.) | 1 (ref.) |
| Mild (< 30 g/day) | 638 | 1,359,856.5 | 46.9 | 0.85 (0.78–0.92) | 0.80 (0.74–0.87) | 0.80 (0.74–0.87) |
| Heavy (≥ 30 g/day) | 26 | 58,294.5 | 44.6 | 0.81 (0.55–1.19) | 0.72 (0.49–1.06) | 0.72 (0.49–1.06) |
| Regular physical activity | ||||||
| No | 5015 | 9,098,471.2 | 55.1 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| Yes | 1041 | 2,082,764.9 | 50.0 | 0.91 (0.85–0.97) | 0.90 (0.84–0.96) | 0.90 (0.84–0.97) |
| Body mass index (kg/m2) | ||||||
| < 18.5 | 170 | 227,153.7 | 74.8 | 1.30 (1.11–1.52) | 1.29 (1.10–1.51) | 1.29 (1.10–1.51) |
| 18.5 to < 23 | 2221 | 3,852,584.0 | 57.7 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| 23 to < 25 | 1608 | 2,980,305.2 | 54.0 | 0.94 (0.88–1.00) | 0.96 (0.90–1.02) | 0.96 (0.90–1.02) |
| 25 to < 30 | 1830 | 3,663,588.8 | 50.0 | 0.87 (0.81–0.92) | 0.91 (0.85–0.97) | 0.91 (0.92–0.85) |
| ≥ 30 | 227 | 457,604.3 | 49.6 | 0.86 (0.75–0.99) | 0.93 (0.81–1.06) | 0.93 (0.81–1.07) |
| Hypertension | ||||||
| No | 3709 | 6,485,930.5 | 57.2 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| Yes | 2347 | 4,695,305.6 | 50.0 | 0.87 (0.83–0.92) | 0.95 (0.90–1.01) | 0.95 (0.90–1.01) |
| Diabetes mellitus | ||||||
| No | 5434 | 9,769,798.4 | 55.6 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| Yes | 622 | 1,411,437.6 | 44.1 | 0.79 (0.73–0.86) | 0.85 (0.78–0.93) | 0.85 (0.78–0.93) |
| Dyslipidemia | ||||||
| No | 4193 | 7,372,120.1 | 56.9 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| Yes | 1863 | 3,809,116.0 | 48.9 | 0.86 (0.81–0.91) | 0.90 (0.85–0.95) | 0.90 (0.85–0.95) |
| Cancer | ||||||
| No | 5932 | 10,892,011.0 | 54.5 | 1(ref.) | 1(ref.) | 1(ref.) |
| Yes | 124 | 289,225.0 | 42.9 | 0.79 (0.66–0.94) | 0.77 (0.64–0.92) | 0.77 (0.64–0.92) |
| Income | ||||||
| Q1 (lowest) | 1388 | 2,544,940.6 | 54.5 | 1 (ref.) | 1 (ref.) | 1 (ref.) |
| Q2 | 1132 | 2,085,588.4 | 54.3 | 1.00 (0.92–1.08) | 1.00 (0.92–1.08) | 1.00 (0.92–1.01) |
| Q3 | 1515 | 2,771,531.0 | 54.7 | 1.00 (0.93–1.08) | 1.01 (0.94–1.09) | 1.01 (0.94–1.09) |
| Q4 (highest) | 2021 | 3,779,176.2 | 53.5 | 0.98 (0.92–1.05) | 0.99 (0.92–1.08) | 1.00 (0.94–1.08) |
IR incidence rate, HR hazard ratio, CI confidence interval.
aAdjusted for age, age at menarche and menopause, parity, duration of breastfeeding, duration of hormone therapy, duration of oral contraceptive use, alcohol consumption, smoking, regular physical activity, income, body mass index, hypertension, diabetes mellitus, dyslipidemia, and cancer.
bAdjusted for age, reproductive period, parity, duration of breastfeeding, duration of hormone therapy, duration of oral contraceptive use, alcohol consumption, smoking, regular physical activity, income, body mass index, hypertension, diabetes mellitus, dyslipidemia, and cancer.