ORs of back pain at each age per 1 SD increases in BMI and waist circumference at the same age estimated from multilevel logistic models (12 326 observations nested within 3426 individuals)
| Model 1* | Model 2† | |||
| OR (95% CI) | P value | OR (95% CI) | P value | |
| BMI | ||||
| Per SD BMI at | ||||
| 36 years | 1.13 (1.01 to 1.26) | 0.03 | 1.12 (1.00 to 1.25) | 0.05 |
| 43 years | 1.11 (1.00 to 1.23) | 0.06 | 1.11 (1.00 to 1.23) | 0.05 |
| 53 years | 1.17 (1.05 to 1.30) | 0.003 | 1.17 (1.05 to 1.30) | 0.003 |
| 60–64 years | 1.31 (1.15 to 1.48) | <0.001 | 1.30 (1.14 to 1.47) | <0.001 |
| 68 years | 1.08 (0.95 to 1.24) | 0.2 | 1.07 (0.94 to 1.22) | 0.3 |
| Waist circumference | ||||
| Per SD WC at | ||||
| 36 years | 1.17 (1.05 to 1.31) | 0.005 | 1.14 (1.02 to 1.27) | 0.02 |
| 43 years | 1.12 (1.01 to 1.24) | 0.03 | 1.08 (0.98 to 1.20) | 0.1 |
| 53 years | 1.16 (1.05 to 1.29) | 0.005 | 1.13 (1.02 to 1.25) | 0.03 |
| 60–64 years | 1.27 (1.12 to 1.44) | <0.001 | 1.21 (1.07 to 1.38) | 0.003 |
| 68 years | 1.12 (0.98 to 1.27) | 0.1 | 1.07 (0.94 to 1.22) | 0.3 |
Please see online supplemental table S5 for results from analyses rerun with BMI and WC modelled in raw units, that is, kg/m2 and cm, respectively.
*Model 1: Includes age as a categorical variable, standardised BMI or WC (mean=0, SD=1) and an age by BMI or age by WC interaction (as appropriate), adjusted for sex (as there was no evidence of a sex by BMI (p=0.2) or a sex by WC (p=0.9) interaction).
†Model 2: Includes age as a categorical variable, standardised BMI or WC (mean=0, SD=1) and an age by BMI or age by WC interaction (as appropriate), adjusted for sex, education, occupational class and time-varying covariates (height, cigarette smoking status, physical activity and symptoms of anxiety and depression).
BMI, body mass index; WC, waist circumference.