An interesting study in Nature titled Genetic Polymorphisms in ADORA2A and CYP1A2 Influence Caffeine’s Effect on Postprandial Glycaemia (open access!) caught my eye. The study investigated how the genetic variants for caffeine metabolism interact with carbohydrate consumption. Quick summary: Consuming caffeine along with carbohydrates changes glucose response for people with certain genetic variants - and doesn't change blood glucose levels for those without the variants.
A little background info on caffeine:Adenosine builds up in the brain all day as you use ATP for energy. As more and more adenosine builds up and binds to the adenosine receptor (ADORA2A), it causes you to get drowsy. This is one reason we feel sleepy and are driven towards sleeping each night. Caffeine also binds to the adenosine receptor, ADORA2A. It isn't the same as adenosine, though, so instead, it blocks the action of adenosine at the receptor. This is why caffeine makes you feel more alert -- due to the lack of adenosine binding to the receptor. (Well... more alert until the caffeine wears off and you suddenly feel really sleepy due to the adenosine that is still hanging around and now able to bind to the receptors.) Adenosine also inhibits norepinephrine and epinephrine release, so when caffeine blocks the receptor, it allows for norepinephrine and epinephrine to be released (surge of energy). Epinephrine, though, also upregulates glucose mobilization... and thus a link to glucose response for caffeine. The CYP1A2 enzyme breaks down the caffeine in the body and those with the genetic variants break it down at different speeds. This is why some people can't drink caffeine after lunch without it affecting their sleep -- and others can drink a cup of coffee at dinner and still sleep well that night. Previous studies show looking at a general population, an increase in glucose response when people consumed caffeine prior to a meal. On the other hand, coffee consumption is associated with a decrease in the risk of type-2 diabetes. The different polyphenols in coffee, though, may come into play here.
Details on the caffeine - carbs - genetics study:The experiment detailed in Nature used a cross-over design where 18 male participants (in their mid-20s) visited a lab two different times to test their response to caffeine and carbs. The participants consumed a 'carbohydrate meal' initially to see what their glucose response was to carbs. This carbohydrate meal seems to be just drinking Gatorade. And the carbohydrate plus caffeine meal was Gatorade with caffeine added. The glucose response was measured for each test condition and the participants were genotyped for their ADORA2A and CYP1A2 variants. The results showed that those with the CC genotype of ADORA2A variant (listed below) had less of a postprandial glucose response without caffeine than they did with caffeine. For the participants with the CT and TT genotype of ADORA2A, there was no difference in glucose response with caffeine vs without.
Genetic Variants that Impact Glucose Response to Carbs:
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