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NMU 20 – Interaction between Caffeine, Alertness, Sleep, Performance and Health Risks

Nutrition / Natural Medicine Update No. 20 August 17, 2016

with Dr. James Meschino


Research Topic: Interaction between Caffeine, Alertness, Sleep, Performance and Health Risks

Source: Journal Nutrition Reviews 2014


We have all heard that caffeine can cause insomnia, increased alertness, enhance athletic performance, cause jitteriness, etc. But how does it do that and can caffeine really improve alertness and performance in a sleep-deprived state?

Well, an excellent review paper on this subject was published in the journal, Nutrition Reviews, in 2014.

Here is how caffeine works in your body: It blocks adenosine receptors from receiving signals from a molecule called adenosine. In turn, this causes a release of:

  • adrenaline
  • dopamine
  • acetylcholine and some other chemical, which in turn:

•    increases alertness,

•     increases blood pressure and heart rate,

•     and increases the pleasure-reward system via dopamine.


Regarding Sleep and Alertness, the brain tracks sleep in two ways:

How long you’ve been awake on any particular day, and your cumulative sleep over the past number of days. If your cumulative sleep has been compromised, your brain builds up a sleep debt that needs to be repaid at some point. The same thing happens if you force yourself to stay awake for a prolonged period of time. The thing about caffeine is that studies show it can TEMPORARILY help you overcome sleepiness in a sleep propensity state – until you can actually get some sleep and repay the sleep debt. In fact, sleep studies show that caffeine ingestion can:

  • improve the ability to stay awake,
  • prevent slowing of reaction time,
  • and reduce the number of lapses of attention in sleep deprived state.

And the effects are dose-dependent, meaning that performance improves as you go from 200 mg of caffeine up to 600 mg of caffeine (One cup of caffeinated coffee has 150-200 mg of caffeine whereas decaffeinated has only 2-12 mg).

However, side effects also increase as the dose increases. Common side effects include the feeling of jitteriness, abdominal pain and nausea. Of note is the fact that caffeine intake in the morning, in the afternoon and overnight, have been shown to counteract the body’s circadian related performance decrements, increasing alertness and improving neurobehavioral functioning, compared to placebo. However, if you push the limit, depriving yourself of the sleep you need, and the pressure for sleep becomes very high, the ingestion of caffeine has little or no effect on preventing performance deficits and mini-sleep attacks that can pose a serious risk, especially if driving or operating heavy equipment, or if attention is required to focus on a task that might put others in danger (i.e. air traffic controller).

In the end caffeine is not a chemical substitute for adequate healthy sleep. It can be used to heighten alertness for short periods to suppress mental and physical fatigue, but constantly accruing sleep debt, and continually using caffeine as a substitute for sleep to sustain your alertness and performance throughout the day and work through the night, can actually lead to some serious consequences. This is especially true for people who use high doses of caffeine, who have heart conditions, high blood pressure, diabetes, intestinal diseases or who do not metabolize caffeine efficiently – in which case it is strongly associated with heart attacks in middle-aged men.

Of note is the fact that short naps are an effective countermeasure that prevent performance decline in situations of increased sleep propensity (feeling the need for sleep) and decreased alertness. How much sleep do you need in any 24-hour cycle?  Most of us need 7-8.5 hours of habitual sleep. More than 28% of Americans sleep less than 7 hours per night, on average. Although some people can get by on less sleep (5-6 hours per night), it is a small minority of people. Some people try to get by on this little sleep and use caffeine to help sustain them. However, the sleep debt accrues, and over time, decreased alertness and performance starts to occur, as often do the signs of impaired and irrational decision-making and the inability to stay compliant with various objectives and goals, including wellness goals, like exercise and healthy eating.  In fact, sleep deprivation is strongly tied to weight gain and increased caloric intake.

The bottom line appears to be: Get your 7-8.5 hours of sleep routinely. If you want to use caffeine to give yourself a gentle performance boost 1-3 times per day, then for most people it doesn’t seem to be harmful. However, routinely using caffeine as a substitute for adequate, healthy sleep will eventually fail you, may cause or aggravate some health problems, create other dangers, reduce your ability to make rational decisions, and likely interfere with your weight loss and wellness objectives.

In the next Lifestyle Medicine Update, I’ll explain how your body breaks caffeine down and how long it stays in your body, along with other aspects of caffeine you may find interesting, such as its ability to help reduce the risk of certain diseases.

As always, I’ve included a link to the review article in the text below.

Caffeine Content of One Cup (8 oz.) of Coffee, Tea, or a 1 oz. Espresso:

  • Brewed Caffeinated Coffee: 150-200 mg
  • Single Serve Caffeinated Coffee: 75-150 mg
  • Decaffeinated Coffee: 2-12 mg
  • Caffeinated Black Tea: 14-70 mg
  • Caffeinated Green Tea: 24-45 mg
  • 1 oz. Espresso Restaurant Style: 47-75 mg



Spaeth AM, Goel N, DInges DF. Cumulative neurobehavioral and physiological effects of chronic caffeine intake: Individual differences and implications for the use of caffeinated energy products. J. Nutrition Review. 2014. Vol 72 (s1): 34-47


Eat Smart, Live Well, Look Great

Dr. Meschino

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