Spilling the Beans on Coffee

By Shannon Kasun, Neuroscience Specialist

Coffee is one of the world's most popular beverages, and for many people, it's an essential part of their morning routine. Its primary active ingredient, caffeine, is the world's most widely consumed psychoactive substance. By acting on the central nervous system, caffeine temporarily increases alertness and enhances several aspects of cognitive performance.

While many people drink coffee simply to wake up, understanding how caffeine works helps explain both its benefits and its limitations.

How Caffeine Works

Throughout the day, your brain produces adenosine, a byproduct of cellular energy consumption that gradually accumulates while you're awake. As adenosine levels rise, they signal your brain that it's time to rest, producing feelings of drowsiness and mental fatigue.

Caffeine has a chemical structure similar to adenosine that it can bind to and block adenosine receptors. By occupying these receptors, caffeine temporarily prevents adenosine from exerting its sleep-promoting effects. The result is increased wakefulness, improved alertness, and reduced perception of fatigue.

Importantly, caffeine does not eliminate adenosine; it simply delays its effects until the caffeine is metabolized.

Caffeinated Cognition

Blocking adenosine has measurable effects on cognition. Research has consistently shown that caffeine can improve:

• Sustained attention

• Focus and concentration

• Mental alertness

• Reaction time

• Vigilance during prolonged tasks

  
  

One review found that a 200 mg dose of caffeine significantly improved reaction time and stimulus detection for approximately two hours compared with a placebo (McLellan et al., 2016). These effects are why caffeine is commonly used before mentally demanding work, long drives, athletic performance, or periods requiring sustained attention.

McLellan et al., 2016; (A) Response times for caffeinated vs. placebo groups (lower times reflect better performance); (B) Stimulus detection for caffeinated vs. placebo groups (higher scores reflect better performance)

Coffee Provides More Than Caffeine

Although caffeine receives most of the attention, black coffee contains hundreds of naturally occurring bioactive compounds. Among the most abundant are chlorogenic acids, a class of polyphenol antioxidants. These compounds help neutralize reactive oxygen species, reducing oxidative stress that can damage cells over time. Chlorogenic acids have also been shown to possess anti-inflammatory properties, making coffee one of the largest dietary sources of antioxidants for many adults. 

Added Sugars Can Offset Coffee's Health Benefits

The health effects of coffee depend largely on what is added to it. Black coffee contains virtually no sugar and very few calories. However, flavored creamers, syrups, whipped cream, and added sugars can substantially increase calorie intake while promoting large fluctuations in blood glucose. Over time, diets high in added sugars have been associated with chronic inflammation, insulin resistance, weight gain, and increased cardiometabolic risk. These metabolic effects can counter many of the health-promoting properties associated with coffee itself.

If your goal is to maximize coffee's nutritional value, black coffee, or coffee with minimal additions, is generally the best choice.

Timing Matters

Because caffeine blocks adenosine, consuming it too late in the day can interfere with your body's natural sleep drive. Even if you fall asleep without difficulty, caffeine consumed later in the afternoon may reduce sleep quality or shorten deep sleep in susceptible individuals. If you experience difficulty falling asleep, consider limiting caffeine to the morning hours. As a general recommendation:

• Avoid caffeine after 12:00 PM if you're particularly sensitive.

• Try to avoid caffeine after 2:00 PM, even if you normally tolerate it well.

  
  

The Bottom Line

Coffee is more than a source of caffeine. Black coffee provides caffeine that can improve focus, alertness, reaction time, and sustained attention, while also supplying antioxidant compounds such as chlorogenic acids that help reduce oxidative stress and inflammation.

To maximize these benefits, keep your coffee simple. Choosing black coffee or minimizing added sugars and creamers allows you to take advantage of coffee's cognitive and health-promoting properties without introducing unnecessary sources of added sugar and excess calories. Likewise, consuming coffee earlier in the day can help preserve healthy sleep—one of the most important pillars of long-term brain health.

References

McLellan, T. M., Caldwell, J. A., & Lieberman, H. R. (2016). A review of caffeine's effects on cognitive, physical and occupational performance. Neuroscience and biobehavioral reviews, 71, 294–312. https://doi.org/10.1016/j.neubiorev.2016.09.001