ORs of back pain at each age per 1 SD increase in BMI and waist circumference at the previous age estimated from multilevel logistic models (8595 observations nested within 3044 individuals)
| Per SD BMI/WC at age | Back pain at age | Model 1* | Model 2† | ||
| OR (95% CI) | P value | OR (95% CI) | P value | ||
| BMI | |||||
| 36 years | 43 years | 1.08 (0.97 to 1.20) | 0.2 | 1.06 (0.96 to 1.18) | 0.3 |
| 43 years | 53 years | 1.17 (1.05 to 1.31) | 0.004 | 1.16 (1.04 to 1.29) | 0.009 |
| 53 years | 60–64 years | 1.32 (1.15 to 1.51) | <0.001 | 1.29 (1.13 to 1.48) | <0.001 |
| 60–64 years | 68 years | 1.11 (0.96 to 1.28) | 0.2 | 1.08 (0.94 to 1.25) | 0.3 |
| Waist circumference | |||||
| 36 years | 43 years | 1.12 (1.01 to 1.24) | 0.04 | 1.08 (0.97 to 1.21) | 0.1 |
| 43 years | 53 years | 1.17 (1.05 to 1.30) | 0.004 | 1.14 (1.02 to 1.26) | 0.02 |
| 53 years | 60–64 years | 1.28 (1.12 to 1.47) | <0.001 | 1.23 (1.07 to 1.40) | 0.003 |
| 60–64 years | 68 years | 1.10 (0.96 to 1.26) | 0.2 | 1.06 (0.92 to 1.21) | 0.4 |
Please see online supplemental table S6 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=0.5) 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.