Table 1—

Fasting glucose and insulin concentrations after paper-filtered regular coffee consumption, caffeine intake, and coffee/caffeine abstinence

Control periodCoffee periodCaffeine periodP*
Study 1 (n = 26)
    Plasma glucose (mmol/l)
        After 2 weeks5.0 ± 0.35.2 ± 0.60.08
        Difference with no coffee0.2 (0.0–0.4)
        After 4 weeks5.1 ± 0.35.1 ± 0.40.94
        Difference with no coffee0.0 (−0.1–0.1)
    Plasma insulin (pmol/l)
        After 4 weeks57.5 ± 18.871.4 ± 31.20.002
        Difference with no coffee13.9 (5.9–21.9)
Study 2 (n = 45)
    Plasma glucose (mmol/l)5.0 ± 0.45.0 ± 0.55.1 ± 0.40.42
        Difference with placebo0.0 (−0.1–0.1)0.1 (0.0–0.2)
    Plasma insulin (pmol/l)51.5 ± 16.056.6 ± 22.454.2 ± 21.10.15
        Difference with placebo4.9 (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.