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/m^{2}), 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 χ

^{2}and t-tests as appropriate.BMI, body mass index; WC, waist circumference.