Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations

Table 1—

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

	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.