Associations between age at menarche and prevalence of chronic LBP in HUNT2 in cross-sectional analysis
| Total number of women in category of age at menarche* | Number of women with chronic LBP | Crude AR of chronic LBP (%) | RR (95% CI) with adjustment for age only | RR (95 % CI) with additional adjustment† | |
| Number of women included | 27 697 | 27 697 | 24 951 | ||
| Age at menarche (year) | |||||
| ≤11 | 2487 | 806 | 32.4 | 1.39 (1.30 to 1.49) | 1.33 (1.24 to 1.43) |
| 12 | 5536 | 1499 | 27.1 | 1.17 (1.11 to 1.24) | 1.13 (1.06 to 1.21) |
| 13 | 7789 | 1953 | 25.1 | 1.08 (1.02 to 1.14) | 1.07 (1.01 to 1.14) |
| 14 | 6861 | 1713 | 25.0 | 1.00 (reference) | 1.00 (reference) |
| 15 | 3759 | 994 | 26.4 | 1.03 (0.96 to 1.10) | 1.04 (0.97 to 1.12) |
| 16 | 975 | 252 | 25.8 | 0.99 (0.89 to 1.11) | 1.02 (0.91 to 1.15) |
| ≥17 | 290 | 83 | 28.6 | 1.12 (0.93 to 1.35) | 1.31 (1.08 to 1.59) |
| P for categorical effect | <0.001 | <0.001 | |||
| P for linear trend | <0.001 | <0.001 | |||
| P for quadratic effect‡ | <0.001 | <0.001 |
*In analysis adjusted for age only.
†Adjustment for age, BMI, physical activity, education, smoking, nulliparity and age at first delivery.
‡In model also including linear effect.
AR, absolute risk; BMI, body mass index; HUNT, Trøndelag Health Study; LBP, low back pain; RR, relative risk.