Caffeine: How Much Is Too Much If You Crave Sleep?

The other day during a presentation on stress and sleep, a man in the audience asked me a question about coffee. How much is too much? he wanted to know.

Research now suggests that people vary in their sensitivity to caffeine. What’s too much coffee for one person may not be too much for another.

Insomniacs should not drink much coffee later in the day

Insomniacs should not drink much coffee later in the dayThe other day during a presentation on stress and sleep, a man in the audience asked me a question about coffee. How much is too much? he wanted to know.

“I sleep about an hour less than I used to,” he explained. “Could coffee have something to do with it?” He added that the cups he normally gets are about twice the size of normal cups. “I drink 4 or 5 big cups.”

I suggested that he cut back on coffee and left it at that. Yes, the number one symptom of excessive coffee consumption is insomnia, and some doctors still urge insomnia sufferers to go cold turkey. But research now suggests that people vary in their sensitivity to caffeine. What’s too much coffee for one person may not be too much for another.

Caffeine and Your Health

In moderation, caffeine isn’t bad for your health. The Mayo Clinic and other trusted medical authorities claim that up to 400 mg of caffeine—or about 4 cups of brewed coffee—is safe for most adults.

In fact, moderate amounts of caffeine may have protective effects, including lowering the risk of developing melanoma, diabetes, and Alzheimer’s and Parkinson’s diseases. A meta-analysis published by the American Heart Association in 2012 concluded that “moderate coffee consumption is inversely associated with risk of heart failure, with the largest inverse association observed for consumption of 4 servings per day.”

Other research suggests that heavier coffee drinking comes with costs. In one study, all-cause mortality was higher in heavy coffee drinkers 54 years and younger than in their counterparts who drank less coffee, leading to the recommendation that young and middle-aged adults avoid drinking more than 4 cups of coffee a day. But in another study, investigators found no relationship between caffeine consumption and all-cause mortality.

Caffeine Sensitivity

Coffee interferes with secretion of the neurotransmitter adenosine: this is what pumps you up and masks sleepiness. But some people are caffeine sensitive and others aren’t—this has largely to do with your genetic make-up. Depending on which variant of the adenosine receptor A2A gene you have, drinking coffee in the evening may degrade your sleep quality and decrease deep sleep—or have no effect at all. Coffee may improve your performance when you’re feeling sleep deprived—or you’ll get no boost from caffeine at all.

Whether and how much caffeine will affect your sleep also depends to some extent on circadian variables and the time of day when you feel most alert. Stanford researchers found that salivary concentrations of caffeine during sleep strongly correlated with wakefulness at night in early risers; less so in intermediate types; and not significantly in night owls. So particularly if you’re an early riser, you’ll need to be careful of when you drink caffeinated beverages and how much you drink.

Metabolism and Elimination

People also differ greatly in the speed at which their bodies metabolize and eliminate caffeine and its metabolites. About 30 to 60 minutes after consumption is the time of maximum plasma concentration. But some people reportedly reach this point in 15 minutes. Metabolism occurs in the liver by an enzyme called CYP1A2. Slight variation in the gene controlling this enzyme is the main determinant of how quickly processing will occur.

Caffeine has an average elimination half-life of 5 to 6 hours. So if you’re like the average person (whatever that is!), the amount of caffeine in your blood will have decreased by half in 5 or 6 hours.

In reality, though, caffeine’s half-life can vary from 2 to 12 hours, depending on constitutional as well as extrinsic factors. Smokers, for instance, metabolize caffeine almost twice as fast as nonsmokers. Pregnant women, in contrast, clear and excrete caffeine more slowly than women who are not pregnant. And as we age, we metabolize all drugs more slowly, including caffeine.

The Take-Away

So how much caffeine is too much? Differences in the way people process caffeine make it hard to make a one-size-fits-all pronouncement. If you’ve got insomnia, try cutting back on caffeine gradually and make sure you’re not indulging too late in the day.

Author: Lois Maharg, The Savvy Insomniac

Lois Maharg has worked with language for many years. She taught ESL, coauthored two textbooks, and then became a reporter, writing about health, education, government, Latino affairs, and food. Her lifelong struggle with insomnia and interest in investigative reporting motivated her to write a book, The Savvy Insomniac: A Personal Journey through Science to Better Sleep. She now freelances as an editor and copy writer at On the Mark Editing.

7 thoughts on “Caffeine: How Much Is Too Much If You Crave Sleep?”

  1. I am addicted to caffeine. One of the source is coffee, no surprise. I used to take 14 cups of coffee a day but able to fall alseep within 5 minutes… but some years later, I have problem to drift off to sleep even if I don’t consume caffeinated drinks or foods for days.

    Luckiy, today I consume no more than 2 cups.

    What is the lesson I learnt? Never think that you are “fine” with caffeinated F&B. As far as sleep is concerned, you can’t ignore the cumulative effect of cafeine in your body. Caffeine has been one of the most common cutting agent for heroin.

    Rely on sleeping pills to sleep or rely on caffeine to stay awake? Both are wrong paths.


    1. Hi West,

      Since you have trouble sleeping, it’s good to hear that you’ve cut your caffeine consumption down to just 2 cups a day.


  2. Caffeine gives us instant awake as it works as a nerve stimulant. However it is not a chemical. It is only plant & seed derived, hence it has lower side effects than narcotic drugs. We should not withdraw from any addiction suddenly to minimize daily intake of caffeine to a level of 2 standard cups per day. Caffeine affects the CNS and the respiratory-reproductive system. Occasionally caffeine can be taken at the time you need more alertness as in the case of study time—it helps in better memory.


  3. Hi Clarkhill,

    While it’s true that caffeine is a naturally occurring chemical substance (as opposed to being manufactured in a laboratory), plant-based chemicals, or phytochemicals, can have quite substantial effects.

    So it’s wise for the caffeine-sensitive to limit the number of cups they have and drink them earlier in the day.


  4. I know I’m pretty caffeine sensitive and for a long time drank only decaffeinated drinks. I’ve been successfully using sleep restriction for 9 months now, it’s an ingrained part of my daily life.

    After reading recent research by the University of Colorado on caffeine’s affects on sleep and the body clock, I’ve now added caffeine back into my daily routine. I have sleep maintenance insomnia plus an early to bed/early to rise body clock, and commonly struggle to stay awake in the evenings, and even late afternoon. But with much experimentation I’ve found one instant coffee late afternoon and another about 2.5 hours before bedtime helps massively, without affecting me getting to sleep. Of course we’re all different in our tolerance to caffeine, and it’s very much trial and error – but an extremely useful tool to be aware of.


    1. Hi Lesley,

      Once again, thanks so much for sharing the details of your experience on this blog.

      The fact that you’ve found caffeine consumed late in the day to be a help rather than a hindrance in establishing robust cycles of sleep and alertness just underscores the main point of this post: concerning caffeine, as with so many other substances we consume, tolerance varies greatly from one person to the next. Your experience suggests that even the caffeine-sensitive may find that it’s useful later in the day.

      So once again, I’m back to the position that for the sleep-challenged, there are no hard-and-fast rules that apply to everyone. And how could it be otherwise, when our internal systems are so complex and our genetic make-up is so varied? Most people who have trouble sleeping are probably best off avoiding caffeine later in the day—but clearly this does not hold true for everyone.

      Through reading and trial-and-error experimentation we can all figure out the things that work for us and the things that don’t. Thanks again for taking time to comment!


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