Characteristics of the MRC National Survey of Health and Development sample included in analysis*
| Male | Female | P value† | |
| Back pain, N (%), at age | |||
| 36 years | 0.08 | ||
| No | 1283 (83.3) | 1256 (80.9) | |
| Yes | 257 (16.7) | 297 (19.1) | |
| 43 years | 0.06 | ||
| No | 1106 (74.6) | 1042 (71.5) | |
| Yes | 377 (25.4) | 415 (28.6) | |
| 53 years | 0.06 | ||
| No | 925 (69.4) | 903 (66.0) | |
| Yes | 407 (30.6) | 465 (34.0) | |
| 60–64 years | 0.06 | ||
| No | 629 (72.1) | 643 (68.1) | |
| Yes | 243 (27.9) | 301 (31.9) | |
| 68 years | 0.02 | ||
| No | 637 (74.1) | 635 (69.2) | |
| Yes | 223 (25.9) | 282 (30.8) | |
| BMI (kg/m2), mean (SD), at age | |||
| 36 years | 24.8 (3.3) | 23.5 (4.1) | <0.001 |
| 43 years | 25.7 (3.5) | 25.1 (4.7) | <0.001 |
| 53 years | 27.4 (4.1) | 27.4 (5.4) | 0.85 |
| 60–64 years | 27.9 (4.1) | 27.9 (5.5) | 0.99 |
| 69 years | 28.1 (4.5) | 28.0 (5.6) | 0.93 |
| Waist circumference (cm), mean (SD), at age | |||
| 36 years | 89.5 (9.3) | 76.9 (11.5) | <0.001 |
| 43 years | 91.8 (9.9) | 77.7 (11.2) | <0.001 |
| 53 years | 97.7 (10.9) | 85.8 (12.8) | <0.001 |
| 60–64 years | 100.8 (11.1) | 92.2 (13.0) | <0.001 |
| 69 years | 100.9 (12.3) | 92.1 (14.0) | <0.001 |
*Maximum n=3426 (1723 males and 1703 females) (this includes participants with a valid measure of back pain, BMI, waist circumference and each covariate for at least one age). Number of participants contributing data at each age: 36 years, n=3093; 43 years, n=2940; 53 years, n=2700; 60–64 years, n=1816; 68–69 years, n=1777 (see online supplemental table S1) for more details).
†P value from formal tests of sex differences using χ2 and t-tests as appropriate.
BMI, body mass index; WC, waist circumference.