Caffeine can decrease insulin sensitivity in humans.

@article{Keijzers2002CaffeineCD,
  title={Caffeine can decrease insulin sensitivity in humans.},
  author={Gerben Keijzers and Bastiaan E. de Galan and Cees J. Tack and Paul Smits},
  journal={Diabetes care},
  year={2002},
  volume={25 2},
  pages={
          364-9
        }
}
OBJECTIVE Caffeine is a central stimulant that increases the release of catecholamines. As a component of popular beverages, caffeine is widely used around the world. Its pharmacological effects are predominantly due to adenosine receptor antagonism and include release of catecholamines. We hypothesized that caffeine reduces insulin sensitivity, either due to catecholamines and/or as a result of blocking adenosine-mediated stimulation of peripheral glucose uptake. RESEARCH DESIGN AND METHODS… 
Caffeine-induced impairment of glucose tolerance is abolished by beta-adrenergic receptor blockade in humans.
TLDR
The data suggest that the insulin antagonistic effects of caffeine in vivo are mediated by elevated epinephrine rather than by peripheral AR antagonism, which is commonly attributed to adenosine receptor (AR) antagonism in skeletal muscle.
Caffeine and glucose homeostasis during rest and exercise in diabetes mellitus.
  • D. Zaharieva, M. Riddell
  • Medicine
    Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme
  • 2013
TLDR
Increased coffee intake has been associated with reduced risk of developing type 2 diabetes in large-scale epidemiological studies and the known effects of caffeine on glucose homeostasis and diabetes metabolism during rest and exercise are highlighted.
The Influence of Acute Caffeine and Coffee Consumption on Glucose Homeostasis: Whole-Body and Tissue-Specific Effects and Mechanisms of Actions
TLDR
Acute consumption of pure caffeine disrupts whole-body glucose homeostasis in healthy, obese, and diabetic participants in a dose-dependent manner and induces insulin resistance acutely, but to a lesser degree than pure caffeine.
Effect of Caffeine on Plasma Glucose and Insulin Response to Mixed Meal Tolerance Test in Type II Diabetes
TLDR
It may be concluded that acute administration of caffeine plus carbohydrate impaired post-prandial glucose metabolism and insulin responses could have implication for the management of type II diabetic patients.
Caffeine ingestion impairs insulin sensitivity in a dose-dependent manner in both men and women.
TLDR
Results showed that caffeine ingestion disrupted insulin sensitivity in a dose-dependent fashion beginning at very low doses (0-1 mg·kg(-1) BW) in both healthy men and women.
Caffeine impairs glucose metabolism in type 2 diabetes.
TLDR
This study tested how oral caffeine affects carbohydrate metabolism in patients with type 2 diabetes, for whom decreases in insulin sensitivity might result in exagger- ated hyperglycemic responses to glucose and other carbohydrates, which would aggravate the glycemic dysregulation found in the disease.
Metabolic and hormonal effects of caffeine: randomized, double-blind, placebo-controlled crossover trial.
TLDR
Evidence is provided that daily caffeine intake reduces insulin sensitivity; the effect persists for at least a week and is evident up to 12 hours after administration.
The effect of caffeine on glucose kinetics in humans – influence of adrenaline
TLDR
It is concluded that adrenaline alone does not account for the effects of caffeine and additional mechanisms must be involved.
Performance effects and metabolic consequences of caffeine and caffeinated energy drink consumption on glucose disposal.
TLDR
Both caffeine-induced performance enhancement and insulin resistance converge with the primary actions of caffeine on skeletal muscle, which may have implications for the development of a number of chronic diseases.
Caffeine ingestion is associated with reductions in glucose uptake independent of obesity and type 2 diabetes before and after exercise training.
TLDR
Caffeine consumption is associated with a substantial reduction in insulin-mediated glucose uptake independent of obesity, type 2 diabetes, and chronic exercise.
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