caffeine Flashcards
background, pharmacology, behavioural effects, tolerance, dependence, health effects (13 cards)
what is the background of caffeine?
sources of caffeine include coffee, tea, chocolate, energy and carbonated drinks
80-90% of people consume regularly
average adult daily intake = 200-400mg
one cup of coffee = ~80-100mg
what is the pharmacology?
absorbed through gastrointestinal tract in about 30-60 minutes
plasma half-life of around 4 hours but usually topped up - people have a rising concentration in blood plasma throughout the day
caffeine converted to metabolites in liver (95% excreted in urine, 2-5% in faeces, rest through saliva)
acts primarily by blocking adenosine (A1, A2A) receptors in the brain
what are the behavioural effects?
depending on dose have different effects on rats and mice
biphasic effect
low to intermediate doses result in a variety of positive subjective effects (Smith et al, 1999)
enhance sports performance
disruption to sleep
negative effects at higher doses (>400mg)
what is a biphasic effect?
low dose = stimulant = high locomotor activity
high dose = reversed = low locomotor activity
what are the positive subjective effects?
increased alertness
reduced tension
reduced reaction time
how does caffeine enhance sports performance?
modest but significant benefits to muscle strength, power and endurance
mechanism of effect still under investigation - could be mediated by effects of alertness and reduced muscle tension, placebo effect
how does caffeine disrupt sleep?
particularly in older adults
when consumed within 6 hour before going to sleep
what are the negative effects of caffeine at higher doses?
tension
jitteriness
anxiety
panic disorder patients may be hypersensitive - panic attacks
what is caffeine tolerance?
subjective effects of caffeine
heavy drinkers can consume coffee before bed (Griffiths and Mumford, 1995)
what was Griffiths et al’s (1990) study into dependence?
abstinence - withdrawal symptoms
even in >100mg/day drinkers (1 cup a day)
headache, drowsiness, fatigue, impaired concentration and psychomotor performance
withdrawal effect lasts a few days of consecutive abstinence but will dissipate
what are the health effects of caffeine?
little to no risk to healthy, non-pregnant adults
what are the acute consumption effects for non-consumers?
high blood pressure
high respiratory rate
high water excretion
what is caffeine’s risk to pregnancy?
associated with infant birth rate
dose-dependent increase in risk of stillbirths
prenatal exposure associated with development effects such as childhood obesity
current guideline = <200mg per day
