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[IP] Caffeine and BG


Below is an abstract from an article in the journal Diabetes (ever 
heard of it?) last year.  This was the research I was thinking about 
when I wrote the last email.  Essentially it says that caffeine reduced 
glucose uptake (into muscle) by 50%.  Notably, it did so *without* 
affecting the cells' insulin signaling mechanisms.  However, they do 
note the increase in adrenaline (epinephrine), but don't make any 
conclusions about it.  Finally, exercise!  It helps maintain 
insulin/glucose sensitivity.

David Jensen
Father to Sigrid, Dx 9/02 @ 11 months, waiting for the pump...

Diabetes 2002 Mar;51(3):583-90	
Caffeine-induced impairment of insulin action but not insulin signaling 
in human skeletal muscle is reduced by exercise.

Thong FS, Derave W, Kiens B, Graham TE, Urso B, Wojtaszewski JF, Hansen 
BF, Richter EA.
Department of Human Biology and Nutritional Sciences, University of 
Guelph, Guelph, Canada. email @ redacted

We investigated the effects of caffeine ingestion on skeletal muscle 
glucose uptake, glycogen synthase (GS) activity, and insulin signaling 
intermediates during a 100-min euglycemic-hyperinsulinemic (100 
microU/ml) clamp. On two occasions, seven men performed 1-h one-legged 
knee extensor exercise at 3 h before the clamp. Caffeine (5 mg/kg) or 
placebo was administered in a randomized, double-blind fashion 1 h 
before the clamp. During the clamp, whole-body glucose disposal was 
reduced (P < 0.05) in caffeine (37.5 +/- 3.1 micromol x min(-1) x 
kg(-1)) vs. placebo (54.1 +/- 2.9 micromol x min(-1) x kg(-1)). In 
accordance, the total area under the curve over 100 min (AUC(0--100 
min)) for insulin-stimulated glucose uptake in caffeine was reduced (P 
< 0.05) by approximately 50% in rested and exercised muscle. Caffeine 
also reduced (P < 0.05) GS activity before and during insulin infusion 
in both legs. Exercise increased insulin sensitivity of leg glucose 
uptake in both caffeine and placebo. Insulin increased insulin receptor 
tyrosine kinase (IRTK), insulin receptor substrate 1-associated 
phosphatidylinositol (PI) 3-kinase activities, and Ser(473) 
phosphorylation of protein kinase B (PKB)/Akt significantly but 
similarly in rested and exercised legs. Furthermore, insulin 
significantly decreased glycogen synthase kinase-3alpha (GSK-3alpha) 
activity equally in both legs. Caffeine did not alter insulin signaling 
in either leg. Plasma epinephrine and muscle cAMP concentrations were 
increased in caffeine. We conclude that 1) caffeine impairs 
insulin-stimulated glucose uptake and GS activity in rested and 
exercised human skeletal muscle; 2) caffeine-induced impairment of 
insulin-stimulated muscle glucose uptake and downregulation of GS 
activity are not accompanied by alterations in IRTK, PI 3-kinase, 
PKB/Akt, or GSK-3alpha but may be associated with increases in 
epinephrine and intramuscular cAMP concentrations; and 3) exercise 
reduces the detrimental effects of caffeine on insulin action in muscle.
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