More Coffee, Less Bang?
Joshua Gowin, Ph.D. in You, Illuminated
A good friend of mine visits the Starbucks near his office at least 3 times a day. He says he can’t work any other way. There’s something alluring to the thought that if you need more energy, you can just gulp down a coffee and, like Popeye after spinach, you become a better version of yourself. But do you really gain from drinking coffee, or is the effect all in your mind?
According to a new study from the University of Bristol, regular caffeine consumers may not receive any benefit in performance. Worse still, they may depend on their favorite beverage just to function at the baseline level of non-consumers. The lackluster effects of caffeine may come as a surprise, but that may be the bitter truth in your cup.
Psychologist Peter Rogers, who has studied the effects of caffeine for nearly 20 years, led this study. Rogers recruited 157 low drinkers of caffeine (less than 40 mg caffeine per day) and 212 high drinkers (more than 40 mg caffeine per day). The low drinkers averaged 10 mg of caffeine per day and the high drinkers averaged 235 mg per day, which is about 2 cups of coffee.
Participants weren’t allowed to drink caffeine between 7pm the night prior to the study and 9:30am the following morning, when they arrived at the laboratory. Participants were excluded if they had a high concentration of caffeine—more than 2 mg— in their saliva the morning of testing.
Rogers tested memory, motor function, and reaction time. He also had participants rate their level of sleepiness and mental alertness. Rogers tested reaction time by asking participants to focus on the center of a computer screen, where either an ‘A’ or ‘B’ would flash. They tried to correctly identify whether they saw an ‘A’ or ‘B’ as quickly as possible. Distracters, such as shapes (stars, squares) or letters (A or B), also appeared next to the target letter to increase the error rate.
The first test occurred at 10:30, not long after the participants arrived and before they consumed any caffeine. Low caffeine consumers were significantly better at identifying A’s and B’s. The high caffeine consumers made nearly 2 more errors on average during the task compared to the low caffeine drinkers. Caffeine withdrawal impaired their vigilance in the morning.
Participants took two pills during the day, first at 11:15am and again at 12:45pm. Half the participants received a placebo and the other half received caffeine (100 mg in the first pill, 150 mg in the second). There were four groups, high caffeine consumers who received placebo or caffeine and low caffeine consumers who received placebo or caffeine.
The second session occurred 45 minutes after the first dose. The third and fourth session occurred 60 and 135 minutes after the second dose.
Overall, the high caffeine consumers who received placebo performed worst on nearly all measures of performance. Caffeine withdrawal significantly impaired their performance. Their performance only got worse as the day wore on. The longer they went without caffeine, the more errors they made.
In contrast, the low caffeine consumers who didn’t get placebo performed equally well across the day. Further, low caffeine consumers performed about equally well if they received placebo or caffeine in most respects. The clear advantage for the group that received caffeine was that they had a higher tapping speed if they received caffeine. Low caffeine consumers who received caffeine responded more quickly in the tasks and they reported feeling less sleepy, but they did not make any fewer errors when identifying A and B.
Based on these results, it appears that high caffeine consumers receive no benefit from caffeine, and their improved performance relative to the first session only represents a return to baseline. Caffeine only brought them back up to the baseline level where low caffeine consumers begin.
The one universal benefit of caffeine was that both high and low caffeine consumers were able to press the space bar faster if they were given caffeine. This enhanced speed may result because caffeine decreases muscle fatigue. A number of triathlete magazines have recommended drinking caffeine before a race and, based on the results of this study, there may be good reason to do so.
Low caffeine consumers may benefit from a brief increase in caffeine consumption to overcome sleepiness. This could come in handy when driving long distances. If they continue to consume caffeine, however, the benefit will wear off and they will become dependent on caffeine to return to their previous baseline level.
The authors concluded, “high consumers treated with caffeine displayed almost the same levels of mental alertness and sleepiness as [low] consumers treated with placebo. This is fully consistent with withdrawal reversal and indicates nearly complete tolerance to these effects of caffeine.”
My friend who drinks three cups a day may not be getting the benefit he thinks from coffee, but like all things in life, there are other reasons for the things we do. He met his girlfriend at a coffee shop and one reason they hit it off was because they kept running into each other at the Starbuck’s where they worked. That’s something you just don’t get from a glass of water.