Caffeine in hot drinks elicits cephalic phase responses involving cardiac activity

Caffeine stimulates both oropharyngeal and gut bitter taste receptors (hTAS2Rs) and so has the potential to elicit reflex autonomic responses. Coffee containing 130 mg caffeine has been reported to increase heart rate for 30 min post-ingestion. Whereas added-caffeine, in doses of 25 to 200 mg, ingested with decaffeinated coffee/tea decreases heart rate 10 to 30 min post-ingestion. This study aimed to clarify caffeine's chemosensory impact. Double-espresso coffees were compared to a placebo-control capsule in a double-blind between-measures design. Coffees tested were regular coffee (130 mg caffeine) and decaffeinated coffee with added-caffeine (0, 67 and 134 mg). Cardiovascular measures from three post-ingestion phases: 1) 0 to 5; 2) 10 to 15; and 3) 25 to 30 min; were compared to pre-ingestion measures. Participants comprised 11 women in the control group and 10 women in the test group. Decaffeinated coffee elicited no changes. Decaffeinated coffee with 67 mg caffeine: decreased dp/dt in Phase 1. Decaffeinated coffee with 134 mg caffeine: increased heart rate in Phases 1 and 2; decreased spontaneous baroreflex sensitivity in Phase 1; and increased diastolic pressure in Phases 2 and 3. Regular coffee: increased heart rate in Phases 1 and 2; decreased dp/dt in all phases; and decreased systolic pressure in Phase 1. Caffeine is the substance in regular coffee which elicits chemosensory autonomic reflex responses, which involves heart activity and the baroreflex. Compared to the caffeine in regular coffee, added-caffeine elicits somewhat different chemosensory responses including a more pronounced pressor effect and resetting of the baroreflex. Caffeine in commonly consumed amounts, as well as modulating body processes by blocking adenosine receptors, can elicit reflex autonomic responses during the ingestion of caffeinated drinks. It is plausible that caffeine stimulates hTAS2Rs, during the ingestion of coffee, eliciting cephalic phase responses. These cephalic phase responses likely result from vagal withdrawal and it is uncertain whether they enhance digestion or not.