Control period | Coffee period | Caffeine period | P* | |
---|---|---|---|---|

Study 1 (n = 26†) | ||||

Plasma glucose (mmol/l) | ||||

After 2 weeks | 5.0 ± 0.3 | 5.2 ± 0.6 | — | 0.08 |

Difference with no coffee | — | 0.2 (0.0–0.4) | — | — |

After 4 weeks‡ | 5.1 ± 0.3 | 5.1 ± 0.4 | — | 0.94 |

Difference with no coffee | — | 0.0 (−0.1–0.1) | — | — |

Plasma insulin (pmol/l) | ||||

After 4 weeks | 57.5 ± 18.8 | 71.4 ± 31.2 | — | 0.002 |

Difference with no coffee | — | 13.9 (5.9–21.9) | — | — |

Study 2 (n = 45†) | ||||

Plasma glucose (mmol/l) | 5.0 ± 0.4† | 5.0 ± 0.5 | 5.1 ± 0.4 | 0.42 |

Difference with placebo | — | 0.0 (−0.1–0.1) | 0.1 (0.0–0.2) | — |

Plasma insulin (pmol/l) | 51.5 ± 16.0 | 56.6 ± 22.4 | 54.2 ± 21.1 | 0.15 |

Difference with placebo | — | 4.9 (0.0–9.8) | 2.8 (−2.1–7.7) | — |

Data are means ± SD or difference (95% CI).

- *
↵*

*P*values are for paired*t*test comparison for study 1 and for existence of an overall treatment effect from ANOVA for study 2. - †
↵† Numbers are lower because of missing blood samples for glucose data after 2 weeks in study 1 (

*n*= 25 for the coffee period,*n*= 24 for the no coffee period) and for glucose data in study 2 (*n*= 41 for the coffee period,*n*= 43 for the caffeine period, and*n*= 42 for the placebo period). - ‡
↵‡ Mean of values obtained after 25 and 28 days.