Quantification of Self-Reported Caffeine Use - Caffeine: Chemistry, Analysis, Function and Effects - page 240

between these two methods. Physiological caffeine concentrations are often
obtained to validate self-reported information. The caffeine concentrations in
blood and saliva samples tend to correlate more closely with self-reported caffeine
use when the samples are obtained within a few hours after caffeine use. If samples
are obtained later, the rate of caffeine metabolism needs to be considered.

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Summary Points

N Caffeine is a mild neurostimulant found in many foods and beverages that
are common in a Western diet.
N Dietary caffeine use can be estimated from an interview or self-report
questionnaire, these measures should query every potential source of dietary
caffeine, and the frequency and volume of each item consumed.
N Caffeine use estimates can be based on retrospective data of past caffeine use
or prospective data of current caffeine use; retrospective measures are faster
but may suffer from memory errors, while prospective measures may be more
accurate but could be recorded during a period of atypical caffeine use.
N Actual caffeine concentrations in coffee and tea vary greatly, and depend on
brewing method and duration.
N When manufacturer information regarding caffeine content is unavailable,
caffeine estimates can be based on average caffeine concentrations reported
in coffee, tea, and chocolate.
N When knowing the exact dose of caffeine ingested is vital to a study, an
alternative to estimating dietary caffeine consumption is to administer a
controlled-dose of caffeine to study participants.
N Peak caffeine absorption occurs 30-70 minutes after ingestion and caffeine
has a half-life of 4-7 hours.
N The rate of caffeine metabolism can be affected by pregnancy, oral steroid
contraceptives, tobacco use, and alcohol consumption.

N

Recent caffeine use can be validated with physiological caffeine concentra-
tions in blood, saliva, or urine samples. Saliva and urine caffeine

concentrations are lower than those in blood, but saliva and urine

concentrations correlate strongly with blood levels.
N Given the rate of caffeine metabolism, the timing of biological specimen
sampling needs careful consideration.
N Under

some circumstances, paraxanthine, the primary metabolite of

caffeine, could also be used as a biological marker of caffeine use.

Key Facts about Methylxanthines in Coffee, Tea, and Cocoa

N

Decaffeinated teas and coffees are not caffeine-free.

N

Green coffee beans are roasted to enhance their flavor. The duration and
temperature of roasting determines the flavor and can change the volume