Effects of Low Doses of Caffeine on Mood, Physiology and Mental Function
It is often assumed that levels of caffeine found in ‘decaffeinated’ beverages are below any psychopharmacological threshold. However, recent findings indicate that caffeine doses as low as 9 mg may be psychoactive. The effects of caffeine have also been shown up to 6 hours post-administration. The study aimed to establish the lowest active dose of caffeine, and to ascertain the duration of any effects.
|Study Design:||Allocation: Randomized
Endpoint Classification: Efficacy Study
Intervention Model: Crossover Assignment
Primary Purpose: Basic Science
|Official Title:||Levels of Caffeine Lower Than Those Found in Decaffeinated Beverages Exert Effects on Cognition, Mood, and Autonomic Activity|
- Assessment of memory, attention, reaction time and subjective mood, measurement of heart rate and blood pressure. Co-monitoring of salivary caffeine levels. [ Time Frame: baseline, 1 hour, 3 hours, 6 hours and 9 hours ]
|Study Start Date:||June 2005|
|Study Completion Date:||November 2005|
The majority of recent caffeine studies have evaluated doses in the range of 75 – 150 mg or 1 – 2 mg/kg (approximately 130 - 260 ml fresh coffee). Such doses produce well characterised effects; including increased ‘alertness’, and improvements to measures of reaction time and sustained attention. A previous study has demonstrated improvements to performance following 9 mg caffeine, which represents the lowest known psychoactive dose of caffeine. A number of these effects, including elevated salivary caffeine levels, were still apparent at 6 hours post-caffeine consumption (9). Findings showing effects of 12.5 and 9 mg caffeine are important as these are approaching the levels found in decaffeinated beverages, which are assumed to have no behavioural or physiological effects. However, despite extensive research in this area, the lower threshold for psychoactive effects has not been established. A randomised, placebo-controlled, double-blind, balanced crossover study was undertaken. 20 young men and women (13 female, mean age 20.7 years, SD 2.4) undertook computerised assessments of memory and attention and rated subjective mood. Autonomic activity and salivary caffeine were co-monitored. Assessment took place at baseline, 1, 3, 6, and 9 hours post-administration of placebo, 2.5, 5, and 10 mg caffeine (on separate days) administered in 150 ml fruit juice.