Relationships between ingestion and gustatory perception of caffeine

We observed that taste detection thresholds for caffeine (CAF) are elevated in habitual CAF users relative to nonusers. A series of experiments were carried out to explore that relationship and assess the influences of salivary CAF and acute vs. chronic CAF ingestion. A significant correlation between CAF ingestion and taste threshold was noted in two studies of U.S. adults, although this was not observed in a parallel study involving an Argentinean population. Acute CAF ingestion (5.5 mg/kg) had no appreciable effect on taste thresholds. Threshold values greatly exceeded even peak salivary CAF levels, indicating that classical taste adaptation was an unlikely influence. Chronic CAF ingestion (450 mg/day for 3 weeks) also had no consistent effect on taste thresholds for CAF or other taste stimuli. Although a number of explanations are considered, we suggest that the sensory phenomenon may reflect preexisting differences between CAF users and nonusers or perhaps an effect of exposure to other bitter and/or CAF-containing foods and beverages.