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LMU 20 – The Impact of Caffeine on Sleep, Alertness, and Performance


LMU 20 – The Impact of Caffeine on Sleep, Alertness, and Performance

Source: Journal Nutrition Reviews 2014

Lifestyle Medicine Update (August 19, 2016)


Caffeine, a widely consumed stimulant found in coffee, tea, and other beverages, has long been associated with various effects on the body, including insomnia, increased alertness, and enhanced athletic performance. But how exactly does caffeine work, and can it genuinely improve alertness and performance in a sleep-deprived state? A comprehensive review paper published in “Nutrition Reviews” in 2014 delves into the science behind caffeine’s effects and potential benefits and risks.

Caffeine’s Mechanism of Action

Caffeine exerts its effects by blocking adenosine receptors, preventing them from receiving signals from the molecule adenosine. As a result, caffeine triggers the release of several chemicals in the body, including adrenaline, dopamine, and acetylcholine. These chemical releases increase alertness, elevated blood pressure, heart rate, and a heightened pleasure-reward system mediated by dopamine.

Sleep and Alertness Regulation

The brain tracks sleep in two primary ways: the duration of wakefulness on a given day and the cumulative rest over several days. When cumulative sleep is compromised, the brain accumulates a “sleep debt” that needs to be repaid at some point. Similarly, staying awake for an extended period increases sleep debt. Caffeine has been shown to temporarily help overcome sleepiness in such sleep-deprived states by improving the ability to stay awake, preventing slowed reaction times, and reducing lapses of attention.

Dosage and Effects

The effects of caffeine are dose-dependent, meaning that performance improves as caffeine intake increases, up to around 600 mg. A typical cup of coffee contains 150-200 mg of caffeine, while decaffeinated coffee has only 2-12 mg. However, side effects like jitteriness, abdominal pain, and nausea become more common as the dose increases.

Caffeine Timing and Circadian Rhythms

Studies have shown that caffeine intake in the morning, afternoon, and overnight can counteract the body’s circadian-related performance decrements, boosting alertness and improving neurobehavioral functioning compared to a placebo. However, suppose one continues to deprive themselves of adequate sleep. In that case, caffeine ingestion will have little effect in preventing performance deficits and mini-sleep attacks, which can be hazardous, especially during activities like driving or operating heavy machinery.

Caffeine as a Substitute for Sleep

While caffeine can temporarily boost performance, it is not a replacement for sufficient, healthy sleep. Relying on caffeine to sustain alertness throughout the day and work through the night can lead to severe consequences, especially for those with heart conditions, high blood pressure, diabetes, or intestinal diseases. People who do not metabolize caffeine efficiently may also face an increased risk of heart attacks, mainly middle-aged men.

The Importance of Adequate Sleep

Most adults require 7-8.5 hours of habitual sleep within a 24-hour cycle. However, over 28% of Americans sleep less than 7 hours per night on average. While some individuals can function with 5-6 hours of sleep, they are the exception rather than the norm. Accumulating sleep debt and consistently using caffeine as a substitute for rest can lead to decreased alertness and performance, impaired decision-making, and difficulties in achieving wellness goals, such as maintaining a healthy weight.

The Bottom Line

For optimal health, it is essential to prioritize adequate sleep, and caffeine should only be used occasionally to give a temporary performance boost. Relying on caffeine to compensate for inadequate sleep is not a sustainable solution and may have adverse health effects. In the next Lifestyle Medicine Update, further aspects of caffeine, such as its metabolism in the body and potential disease-preventing properties, will be explored.


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

Dr. James Meschino


Dr. James Meschino, DC, MS, ROHP, is an educator, author, and researcher having lectured to thousands of healthcare professionals across North America. He holds a Master’s Degree in Science with specialties in human nutrition and biology and is recognized as an expert in the field of nutrition, anti-aging, fitness, and wellness as well as the author of numerous books.

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