Many people believe that drinking more coffee before a workout leads to better results. A new review of scientific studies suggests this may not be true. The research indicates that a small amount of caffeine may provide most of the performance benefit, without the side effects that come with larger doses.
About the study
Scientists have studied caffeine as a performance aid for decades. The evidence that it helps endurance is strong. What has been less clear is whether taking more caffeine leads to greater benefits or simply more side effects. To answer this question, researchers looked at 48 randomized, placebo-controlled trials. These studies included 689 participants. The team compared how low, moderate, and high doses of caffeine affected performance in aerobic time trials.
Low doses were defined as up to 3 milligrams per kilogram of body weight. Moderate doses were 4 to 6 milligrams per kilogram. High doses were anything above 6 milligrams per kilogram. To make the results comparable, the researchers only included studies that used pure caffeine in capsule or liquid form. They did not include coffee, energy drinks, or gum because the caffeine content in those products can vary by more than 50 percent.
Low doses nearly matched moderate doses
Low doses of caffeine, roughly 1.3 to 3 milligrams per kilogram of body weight, produced a clear improvement in time-trial completion time. Moderate doses of 4 to 6 milligrams per kilogram also improved performance. But when researchers looked at the actual race-time improvements across the studies, the difference between the two dose ranges was very small. Low doses corresponded to an average improvement of about 2.14 percent. Moderate doses came in at about 2.18 percent.
In other words, doubling or tripling caffeine intake did not get athletes meaningfully further across the finish line. The moderate-dose group also showed more variability across studies. This means the results were less consistent. The low-dose group showed a more uniform effect. The researchers noted that two studies had a large influence on the moderate-dose results. Removing those studies from the analysis changed the overall picture. No studies using high caffeine doses, above 6 milligrams per kilogram, met the inclusion criteria for time-trial performance. That end of the spectrum remains largely unknown.
Why caffeine affects people differently
The review also looked at how genetics plays a role in caffeine response. A gene called CYP1A2 controls an enzyme that breaks down about 95 percent of the caffeine a person consumes. Depending on which version of this gene a person carries, caffeine may work very differently. People who carry the CC variant of CYP1A2, commonly classified as slower caffeine metabolizers, may see a weaker or less consistent performance response. Those who carry the AA or AC variants tend to show energetic benefits from caffeine more often.
The review also pointed to early evidence that other genetic factors may play a role. These include variations in adenosine receptors, the receptors in the brain that caffeine blocks to reduce the sense of effort. That research is still developing, but it helps explain why two people can take the same dose and have completely different experiences.
Finding the right amount
If a person uses caffeine before workouts or races, a good starting point is a low dose. A dose of roughly 1.3 to 3 milligrams per kilogram of body weight, taken about 60 minutes before exercise, produced consistent performance improvements across the included studies. For a person weighing 70 kilograms, that would be about 90 to 210 milligrams of caffeine. A standard cup of coffee contains anywhere from 80 to 200 milligrams of caffeine depending on how it is brewed. This means a morning cup may already put a person in that effective range.
The case for starting low is also supported by the side effects that come with higher doses. High caffeine intake is commonly linked to anxiety, heart palpitations, headaches, poor sleep, and gastrointestinal issues. If moderate doses offer only a small real-world advantage over low doses, the risk-benefit calculation shifts in favor of the smaller amount. This is especially true for people who are sensitive to caffeine or who train in the evening.
Key takeaway
Low caffeine doses, between 1.3 and 3 milligrams per kilogram of body weight, improved endurance time-trial performance by about 2 percent. This nearly matched the real-world benefit of moderate doses, which were 4 to 6 milligrams per kilogram. Because higher doses come with a greater risk of side effects and no proportional performance gain, starting with a low dose is a sensible strategy for most people.
