My wife is often telling me that drinking coffee later in the day will lower my "quality of sleep." Is this so? For an example of a bit beefier of a source for this claim, consider THIS blog post, featuring the following:

Today’s NZ Sunday Star Times had a short article on how and why any amount of caffeine can affect your sleep, from research done at Massey University’s Sleep / Wake Research Centre.

Myth: Coffee has no effect on me. I can have a coffee right before bed and have no problem going to sleep.

Fact: If you ingest enough caffeine you may have trouble getting off to sleep but in a regular caffeine consumer this is not usually where the damage is done. Caffeine adversely affects the quality of your sleep.

So, I wandered over to the link to the Massey/Wake Research Centre, but the link was only to their home page. I clicked around to their list of PUBLICATIONS and searched the page for the terms "caffeine" or "coffee." I got one hit: The suitability of a caffeinated energy drink for night-shift workers. Physiology and Behaviour. The abstract is HERE, but I can't get the full article.

They tested 15 night shift workers, giving them energy drinks containing actives (caffeine, etc.) during one period and a placebo energy drink during another period and monitored their "wakefulness" and sleep. The abstract certainly seems to indicate some effect, but I'm hazy as to what this might mean:

Sleep efficiency was also significantly reduced from 91.8+/-.9% [placebo energy drink] to 84.7+/-2.7% [active energy drink] (p<.05).

My questions are:

  • Are there other studies/sources answering whether caffeine later in the day reduces one's quality of sleep?
  • If quality is reduced, is there any way to translate that into approximate perceived effect? As in, are there any sources for what "quality of sleep" is necessary to feel refreshed? Or, per the above, what is "sleep efficiency" and how much difference does 7% make?

I ask the last question because I think there's something to the following hypothetical study:

  • Measure the "quality of sleep" of many subjects during various night's sleeps
  • Ask them in the morning to report their perceived "refreshed-ness"
  • Compare the measured quantity with their answers

If measured and reported do not correlate, then "quality of sleep" probably isn't the quantity any of us cares about with respect to living life.


Thanks for the answers, everyone! I think I found a source that takes the cake, though. HERE is a full-text meta-analysis of many, many studies about caffeine, including its effects on sleep. See the section entitled "Effects of caffeine on sleep."

To answer my own question, I'd have to say that the answer is both "yes" and "no."

  • Yes: From an analytical/research/measurement perspective, it appears that there have been a considerable number of studies showing that caffeine does, in fact, affect sleep quality (duration, efficiency, latency, etc.).
  • No: From what I would consider a practical perspective, two bolded studies below show that despite being able to measure caffeine's effects on sleep... these measurements do not seem to correlate with mood or performance the next day. Thus, I'm left to ask if I should/need to care about such measured effects in daily life.

To dig into the linked paper above, here are the main points:

  • Caffeine increases sleep latency (the time required to fall asleep from being awake ([LINK}(http://en.wikipedia.org/wiki/Sleep_onset_latency)). [1]
  • Caffeine reduces sleep duration. [2]
  • Caffeine administered in the early morning can affect sleep. [3]
  • Individuals in studies have reported that they can consume caffeine bedtime with no adverse effects. [4] [5]
  • High caffeine consumers appear less report sleep disturbance infrequent consumers. [6]
  • Tolerance develops to the effects of caffeine sleep. [1]
  • There are no withdrawal effects on sleep once caffeine consumption is ceased. [7]
  • It is unclear whether there is any correlation between measured sleep disturbance and changes in mood and performance on the following day. [8]
  • It is easy to demonstrate that caffeine consumed late at night produces effects on sleep; it is difficult to show the same for high consumption levels of caffeine in general.
  • An inverse relationship has been found between daily caffeine consumption and sleep duration, but no significant relationship has been found between caffeine consumption and sleep satisfaction. [2]
  • Several studies are listed which found little evidence to correlate caffeine consumption and and sleep. [9] [10] [11]

The three conclusions drawn from the meta-analysis are:

  • Over 3 mg/kg of caffeine in a single beverage consumed in the late evening will both increase sleep latency and reduce duration. Smaller amounts vary considerably between individuals, and there is evidence to support that high consuming individuals are more resistant to sleep side effects of caffeine.
  • Impacts on next-day behavior after caffeine-induced sleep effects is not known. Neither are effects on long term health (assuming long term health effects related to sleep alterations, but it's not specified).
  • High levels of caffeine have not been strongly related to sleep parameters, but this may be due to the scheduling of consumption as to not adversely affect sleep (i.e. not drinking caffeine later in the day.

I bolded a couple of studies, as their methods indicate that patients were asked to self-report. I see potential sources for error and bias in methods like these. I happen to drink a lot of coffee, and could see having a vested interest in making myself look better, and thus skewing responses toward the "little/no adverse effects" end of the spectrum.

I'll close by saying that further studies would be helpful to 1) eliminate self-reporting bias (use objective measurements rather than subjective questions) and 2) examine more handles than just "mood" and "performance" to establish/dis-establish the connection between sleep disturbance and any practical effects on the life/experience of the individual.

[1] Zwyghuizen-Doorenbos, A., Roehrs, T.A., Lipschutz, L., Timms, V., Roth, T., 1990. Effects of caffeine on alertness. Psychopharmacology 100, 36–39.
[2] Hicks, R.A., Hicks, G.J., Reyes, J.R., Cheers, Y., 1983. Daily caffeine use and the sleep of college students. Bulletin of the Psychonomic Society 21, 24–25.
[3] Landolt, H.P., Werth, E., Borbely, A.A., Dijk, D.J., 1995. Caffeine intake (200mg) in the morning affects human sleep and EEG power spectra at night. Brain Research 675, 67–74.
[4] Colton, T., Gosselin, R.E., Smith, R.P., 1967. The tolerance of coffee drinkers to caffeine. Clinical Pharmacology and Therapeutics 9, 31–39.
[5] Levy, M., Zylber-Katz, E., 1983. Caffeine metabolism and coffee attributed sleep disturbances. Clinical Pharmacology and Therapeutics 33, 770–775.
[6] Snyder, S.H., Sklar, P., 1984. Behavioral and molecular actions of caffeine: focus on adenosine. Journal of Psychiatric Research 18, 91–106.
[7] Searle, G.F., 1994. The effect of dietary caffeine manipulation on blood caffeine, sleep and disturbed behaviour. Journal of Intellectual Disability Research 38, 383–391.
[8] Smith, A.P., Maben, A., Brockman, P., 1993b. The effects of caffeine and evening meals on sleep and performance, mood and cardiovascular functioning the following day. Journal of Psychopharmacology 7, 203–206.
[9] Lee, K.A., 1992. Self-reported sleep disturbances in employed women. Sleep15, 493–498.
[10] Greenwood, K.M., Rich, W.J., James, J.E., 1995. Sleep hygiene practices and sleep duration in rotating-shift shiftworkers. Work and Stress 9, 262–271.
[11] Bliwise, N.G., 1992. Factors related to sleepquality in healthy elderly women. Psychology and Aging 7, 83–88.


It depends on what you are used to:

(quote and link from wikipedia): Caffeine tolerance develops very quickly, especially among heavy coffee and energy drink consumers. Complete tolerance to the sleep disruption effects of caffeine develops after consuming 400 mg of caffeine 3 times a day for 7 days. Complete tolerance to subjective effects of caffeine was observed to develop after consuming 300 mg 3 times per day for 18 days, and possibly even earlier. http://www.acnp.org/G4/GN401000165/CH161.html

In fact, when I was heavily addicted to coffee, I even would miss sleep due to withdrawal effect. Also this has been described in literature: http://dx.doi.org/10.1007%2Fs00213-004-2000-x (Even though the abstract does not mention insomnia, many references are given to studies which mention insomnia as an effect of caffeine withdrawal. It was not included in the abstract because the data were not quantitative)

  • 2
    Unfortunately, personal anecdotes aren’t a reliable reference. Skeptics.SE only accepts reliable, independent research as references. – Konrad Rudolph Jun 8 '11 at 8:38
  • Thanks for your comment. I thought my statements were so obvious that this was unneeded, so I've updated my post. – johanvdw Jun 8 '11 at 12:04
  • I hardly ever drink caffeine, but when I do I am typically referred to as a 'squirrel on speed' by those who know me. Sometmes it is handy. ;) – hudsonsedge Jun 9 '11 at 4:00

Sleep efficiency: the number of minutes of sleep divided by the number of minutes in bed. Normal is approximately 85 to 90% or higher. From Wikipedia, but I assure that is the standard definition among sleep researchers.

I think this is a large effect (did I do the math right? are those CIs or SDs?), but it's a small sample. They didn't detect any bad "hard" outcomes (lower performance, more lapses, more sleepiness), but this might be a power problem. But then again, this one night didn't press levels down to anything anormal.

Also, sleep efficiency is not the best measure of sleep quality (polysomnographs give better estimates of NREM sleep, stage changes, etc.). Essentially they did what you had in mind already, right? But it was just one night and they call for longer tests (I have access to the full text, but I probably am not allowed to send it to you?!).

From their conclusion:

This investigation is the first of its kind to examine the effects of FEDs on sleep. It was illustrated that the FEDs administered during a simulated first night shift did not significantly impact on SOL nor the amount of SWS obtained during subsequent daytime recovery sleep. While TST was reduced significantly, by 29.1 min, post recovery-sleep performance was unaffected. Potentially however, is this TST reduction occurs over successive days, it may contribute to increased sleepiness during night-shifts. This investigation indicates that FEDs do have the potential to be used by the night-shift working population. It is evident however, that if they are to be used regularly, further investigation is required to maximise their positive impact.

Maybe you want to go through their references and those who cite them, if you care about this research area.

  • Yes, no need to send the full text. Thanks for the conclusion. While the study seemed to be on the right track, you're correct: it's one study with a small sample size examining two night's sleeps (one with active, one without), and the conclusion, in my opinion, is quite weak: they seem to call for further investigation, indicating that they know they haven't answered the question yet. – Hendy Jun 8 '11 at 11:18
  • @Hendy Totally agree. Maybe you'll find something bigger in the references, but I'm not sure. Sleep research tends to be pretty expensive (polysomnography) and badly funded (I don't think Red Bull cares to validate its claims) and psychological therapies for sleep disorders aren't big moneymakers (and I guess caffeine doesn't count as an anti-sleep disorder drug). – Ruben Jun 8 '11 at 12:06

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