HRs for incident RA, and incident seropositive or seronegative RA phenotypes, according to body mass index (BMI) at 18-years-old in Nurses’ Health Study and Nurses’ Health Study II
| BMI at age 18 | Nurses’ Health Study | Nurses’ Health Study II | Pooled HR (95% CI) | p Het† | ||||
|---|---|---|---|---|---|---|---|---|
| Number of cases/ person-years | Age-adjusted HR (95% CI) | Multivariable HR (95% CI)* | Number of cases/ person-years | Age-adjusted HR (95% CI) | Multivariable HR (95% CI)* | |||
| All RA cases | ||||||||
| All RA | ||||||||
| 18.5–20.0 | 245/813 471 | 1.00 | 1.00 | 111/740 798 | 1.00 | 1.00 | 1.00 | |
| 20.0–22.9 | 307/1 065 987 | 0.96 (0.81 to 1.13) | 0.95 (0.80 to 1.12) | 153/780 354 | 1.30 (1.02 to 1.66) | 1.27 (0.99 to 1.62) | 1.08 (0.81 to 1.43) | 0.056 |
| 23.0–24.9 | 107/286 070 | 1.23 (0.98 to 1.54) | 1.18 (0.93 to 1.48) | 36/200 835 | 1.20 (0.82 to 1.74) | 1.10 (0.76 to 1.61) | 1.16 (0.95 to 1.40) | 0.780 |
| ≥25.0 | 93/225 192 | 1.36 (1.07 to 1.73) | 1.26 (0.99 to 1.61) | 53/197 317 | 1.78 (1.28 to 2.46) | 1.53 (1.10 to 2.14) | 1.35 (1.11 to 1.64) | 0.355 |
| p trend | 0.004 | 0.029 | 0.001 | 0.024 | 0.002 | |||
| Seropositive RA | ||||||||
| 18.5–20.0 | 145/755 465 | 1.00 | 1.00 | 68/725 995 | 1.00 | 1.00 | 1.00 | |
| 20.0–22.9 | 185/992 789 | 0.97 (0.78 to 1.21) | 0.96 (0.77 to 1.19) | 99/763 654 | 1.39 (1.02 to 1.89) | 1.35 (0.99 to 1.83) | 1.11 (0.80 to 1.55) | 0.080 |
| 23.0–24.9 | 73/265 486 | 1.42 (1.07 to 1.88) | 1.34 (1.01 to 1.78) | 27/195 732 | 1.49 (0.95 to 2.33) | 1.36 (0.87 to 2.13) | 1.35 (1.06 to 1.71) | 0.957 |
| ≥25.0 | 57/206 859 | 1.42 (1.05 to 1.94) | 1.30 (0.95 to 1.77) | 38/191 338 | 2.10 (1.41 to 3.13) | 1.81 (1.21 to 2.70) | 1.49 (1.08 to 2.06) | 0.201 |
| p trend | 0.004 | 0.025 | <0.001 | 0.005 | <0.001 | |||
| Seronegative RA | ||||||||
| 18.5–20.0 | 100/810 187 | 1.00 | 1.00 | 43/739 391 | 1.00 | 1.00 | 1.00 | |
| 20.0–22.9 | 122/1 061 975 | 0.93 (0.72 to 1.22) | 0.93 (0.71 to 1.21) | 54/778 574 | 1.17 (0.78 to 1.75) | 1.15 (0.77 to 1.71) | 0.99 (0.79 to 1.23) | 0.387 |
| 23.0–24.9 | 34/284 604 | 0.96 (0.65 to 1.41) | 0.93 (0.63 to 1.37) | 9/200 346 | 0.76 (0.37 to 1.56) | 0.71 (0.34 to 1.45) | 0.87 (0.62 to 1.23) | 0.519 |
| ≥25.0 | 36/223 960 | 1.29 (0.88 to 1.89) | 1.22 (0.83 to 1.79) | 15/196 709 | 1.28 (0.71 to 2.31) | 1.12 (0.62 to 2.02) | 1.19 (0.86 to 1.64) | 0.810 |
| p trend | 0.310 | 0.478 | 0.654 | 0.980 | 0.570 | |||
| RA onset ≤55 years of age | ||||||||
| All RA | ||||||||
| 18.5–20.0 | 84/375 856 | 1.00 | 1.00 | 95/700 885 | 1.00 | 1.00 | 1.00 | |
| 20.0–22.9 | 123/497 886 | 1.12 (0.85 to 1.48) | 1.11 (0.84 to 1.46) | 131/737 890 | 1.30 (1.00 to 1.70) | 1.27 (0.98 to 1.66) | 1.19 (0.98 to 1.44) | 0.481 |
| 23.0–24.9 | 39/131 270 | 1.31 (0.89 to 1.92) | 1.26 (0.86 to 1.85) | 29/190 217 | 1.12 (0.74 to 1.70) | 1.04 (0.69 to 1.58) | 1.16 (0.87 to 1.54) | 0.507 |
| ≥25.0 | 44/108 004 | 1.82 (1.26 to 2.62) | 1.70 (1.18 to 2.47) | 49/187 052 | 1.91 (1.35 to 2.69) | 1.66 (1.17 to 2.36) | 1.68 (1.30 to 2.17) | 0.924 |
| p trend | 0.001 | 0.005 | <0.001 | 0.011 | <0.001 | |||
| Seropositive RA | ||||||||
| 18.5–20.0 | 52/343 779 | 1.00 | 1.00 | 56/686 316 | 1.00 | 1.00 | 1.00 | |
| 20.0–22.9 | 74/457 265 | 1.06 (0.74 to 1.52) | 1.05 (0.73 to 1.49) | 84/721 457 | 1.43 (1.02 to 2.00) | 1.39 (0.99 to 1.94) | 1.21 (0.92 to 1.60) | 0.262 |
| 23.0–24.9 | 28/119 954 | 1.51 (0.95 to2.40) | 1.45 (0.91 to 2.30) | 24/185 247 | 1.60 (0.99 to 2.59) | 1.49 (0.92 to 2.41) | 1.47 (1.05 to 2.05) | 0.933 |
| ≥25.0 | 28/96 989 | 1.90 (1.20 to 3.02) | 1.74 (1.09 to 2.78) | 34/181 147 | 2.28 (1.49 to 3.50) | 1.99 (1.29 to 3.06) | 1.87 (1.36 to 2.56) | 0.686 |
| p trend | 0.003 | 0.010 | <0.001 | 0.002 | <0.001 | |||
| Seronegative RA | ||||||||
| 18.5–20.0 | 32/373 858 | 1.00 | 1.00 | 39/699 511 | 1.00 | 1.00 | 1.00 | |
| 20.0–22.9 | 49/495 352 | 1.19 (0.76 to 1.86) | 1.19 (0.76 to 1.86) | 47/736 139 | 1.13 (0.74 to 1.72) | 1.11 (0.72 to 1.70) | 1.15 (0.84 to 1.56) | 0.817 |
| 23.0–24.9 | 11/130 352 | 0.98 (0.49 to 1.94) | 0.95 (0.48 to 1.89) | 5/189 733 | 0.46 (0.18 to 1.17) | 0.43 (0.17 to 1.10) | 0.68 (0.32 to 1.46) | 0.184 |
| ≥25.0 | 16/107 182 | 1.71 (0.94 to 3.12) | 1.64 (0.89 to 3.01) | 15/186 461 | 1.40 (0.77 to 2.54) | 1.22 (0.67 to 2.24) | 1.41 (0.92 to 2.17) | 0.506 |
| p trend | 0.150 | 0.203 | 0.599 | 0.918 | 0.361 | |||
Bold typeface indicates significant results.
*Adjusted for age, community median income, smoking (pack-years), alcohol use (<5.0, 5.0-<15.0, ≥15 g/day) and physical activity (0–3, 3–9, 9–18, 18–27, ≥27 METs/week).
†p Value for test of heterogeneity (het) between the 2 cohorts. Risk estimates were pooled by using a DerSimonian and Laird random-effects model.
MET, metabolic equivalent; RA, rheumatoid arthritis.