The first shot of coffee doesn't necessarily make you alert, say University of Bristol researchers.
Possibly regular coffee drinkers quickly develop a tolerance to caffeine. So the reason you may feel more alert is because the strong brew simply reverses the tiring effects of acute caffeine withdrawal, the British scientists said. The point is though caffeine is valued as a psychostimulant, it is also anxiogenic (something that causes anxiety).
The Bristol study investigated whether habitual intake might moderate the anxiogenic effect of caffeine. Participants were 162 non-/low (NL) and 217 medium/high (MH) caffeine consumers.
In a randomized, double-blind, parallel groups design they rated anxiety, alertness, and headache before and after 100 mg caffeine and again after another 150 mg caffeine given 90 min later, or after placebo on both occasions.
Caffeine did not increase alertness in NL participants. With frequent consumption, substantial tolerance develops to the anxiogenic effect of caffeine, even in genetically susceptible individuals, but no net benefit for alertness is gained, as caffeine abstinence reduces alertness and consumption merely returns it to baseline.
Lead author Professor Peter Rogers, said: 'Our study shows that we don't gain an advantage from consuming caffeine - although we feel alerted by it, this is caffeine just bringing us back to normal.'
The research was funded by a grant from the Biotechnology and Biological Sciences Research Council, UK.