I love drinking coffee in the morning.  In addition to enjoying the taste of coffee, I use caffeine for the same reason most people do – it improves alertness and performance.  But, it’s easy to misuse if you don’t understand how it works and every medical student and resident has learned this the hard way….

The half-life of caffeine is about 5 hours.  But – the half-life is variable and is probably genetically determined.  Caffeine is eliminated by 1st order kinetics.  In other words (in caffeine equivalents):

  • 4 cups of coffee at 8 am =
  • 2 cups of coffee at 1pm =
  • 1 cup of coffee at 6pm =
  • 1/2 cup coffee at 11pm

Caffeine is a diuretic.  This is mostly true if you are a novice, but not so true if you are ingesting your usual amount. (Griffin, R. J.; Griffin, J. (2003). “Caffeine ingestion and fluid balance: a review”. Journal of human nutrition and dietetics 16 (6):411)

25-50 mg of caffeine improves alertness.  Up to 100 mg is probably ok  for most of us, but more can lead to being jittery, anxious and will absolutely affect the quality of your sleep.  Truly excessive intake can lead to serious side effects.

It’s a drug and therefore there is an optimal way to dose it.  If you take in a lot of caffeine all at once (the triple grande whatever) , it will last longer (see half life above) but it’s pharacologically better to dose about every 4-5 hours with about 50 mg of caffeine to avoid the negative side effects.

Different drinks have different amounts of caffeine. For example,~50mg of caffeine is found in:

  • 1 oz of 5hr energy  (138 mg/2 oz)
  • 12 oz of most caffeinated sodas (~40-50 mg/12 oz)
  • 4 oz of brewed coffee (108 mg/8oz)
  • 1 oz of espresso coffee (77 mg/1.5 oz)
  • 8 oz of brewed tea (~50 mg/8 oz)

Napping will improve studying more than caffeine.  I know it seems easier to just keep studying and drink the coffee, but there are data that suggest you’ll do better if you take a nap.

Behav Brain Res. 2008 Nov 3;193(1):79-86. Epub 2008 May 8. Comparing the benefits of caffeine, naps and placebo on verbal, motor and perceptual memory.  Mednick SC, Cai DJ, Kanady J, Drummond SP.

Trivia for rounds….

1.  Caffeine was discovered in 1819 by a German chemist (Friedrich Ferdinand Runge)

2.  It exists in plants to serve as a pesticide

3.  It works by being an competitive antagonist to adenosine receptors

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2 thoughts on “Caffeine

  1. So, do people who drink more coffee get less insect bites (or if not, at least do the insects DIE)?

    I liked seeing how the half life of caffeine related to affects on sleep hours later. Thanks!

  2. Pingback: A Hundred Words for “Tired” | wellnessrounds

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