Variable | Regression coefficient (95% CI) |

1976–1978 | |

Smoking | -2.0 (-3.1– -0.3) |

BMI | |

25–30 kg·m^{−2} | -0.3 (-1.0–0.8) |

>30 kg·m^{−2} | -0.9 (-2.1–1.1) |

Asthma | -2.3 (-9.4–4.6) |

1991–1994 | |

Smoking | -2.9 (-5.9– -0.3) |

BMI | |

25–30 kg·m^{−2} | -1.4 (-2.2– -0.6) |

>30 kg·m^{−2} | -3.3 (-5.2– -1.6) |

Asthma | -10.7 (-13.4– -7.9) |

2001–2004 | |

Smoking | -4.6 (-5.8– -3.4) |

BMI | |

25–30 kg·m^{−2} | -1.5 (-2.9– -0.3) |

>30 kg·m^{−2} | -4.9 (-6.1– -3.8) |

Asthma | -14.2 (-16.5– -12.1) |

Data are presented in the units of the dependent variable (FEV

_{1}% pred). Smoking and asthma status were included in the model as dichotomous variables (with nonsmoker and no asthma as reference), whereas body mass index (BMI) was included in the model in three categories,*i.e.*BMI >25, BMI 25–30 and BMI >30 (with BMI <25 as reference).