Adam C. Stewart
Caffeine can give an energy boost and significantly improve performance, but concerns about potential disadvantages (such as sleep disorders or heart problems) are common. This article describes both the advantages and disadvantages of caffeine consumption.
Note: This article was the cover article of MASS Research Review for February 2024 and is a review of a recent article by Marcus et al. If you want more content like this, subscribe to MASS.
Caffeine is one of the few fitness-related topics where the passion of fitness enthusiasts is equaled, if not surpassed, by the general public. The interest of trainers is understandable, because meta-analyzes show that caffeine can acutely improve a variety of performance results, including strength and power (as described in this mass video). The interest of non-weightlifters is equally understandable, because everyone could use a morning energy boost and caffeinated drinks, such as tea and coffee, occupy a prominent place in many cultures. About 85% of American matures consume a caffeinated drink daily (2), and some estimates place their average daily caffeine intake just north of 200 mg/day (3). It may seem like a lot, but the average daily caffeine intake in Sweden and Finland exceeds 400 mg/day (3). To date, one of the highlights of my career has been presenting at an awesome sports science conference in Finland – after going there in a relatively cold month, I can vouch for the estimate of 400+ mg/day. Coffee was practically always at hand, and as a coffee lover, I was in heaven.
However, many governments advise citizens to limit their daily caffeine intake to no more than 300 to 400 mg/day, while some point out that a daily intake of more than 200 mg/day can lead to undesirable side effects such as nervousness or anxiety (4). Caffeinated drinks are also in the news after two lawsuits recently attributed fatal cardiac arrhythmias to the consumption of a particular product in an American restaurant chain. I wouldn’t dare to fall between a coffee drinker and his morning dose of caffeine, but we shouldn’t ignore the potential disadvantages of caffeine just because we appreciate its most desirable properties. Instead, we should look at the evidence to see if the advantages outweigh the disadvantages, and that’s exactly what this article is about. Marcus et al. (1) have recently studied the effects of acute caffeine consumption on cardiac arrhythmias, the number of daily steps and sleep results. So let’s dive in and see what you have found.
Objective and assumptions
Objective
The purpose of the study currently under review was “to investigate the effects of caffeinated coffee on cardiac ectopia and cardiac arrhythmias, the number of daily steps, minutes of sleep and serum glucose levels.”
Hypothesis
The researchers did not put forward an explicit hypothesis.
Themes and methods
The current study examined 113 potential participants and finally included 100 eligible matures who consumed caffeinated coffee at least once a year. The researchers excluded participants who had certain heart issues, were taking certain medications that affected the heartbeat or had a medical reason for avoiding coffee. The study was a randomized crossover trial; Participants were asked to consume caffeinated coffee or avoid caffeine in a series of seven 2-day sequences (On-Off or Off-on), the study lasting a total of 14 days. Each morning, the participants received an SMS informing them of their assigned status (caffeinated coffee or no caffeine). These tasks were sent in random order with two-day sequences to ensure that the participants would never spend more than two consecutive days consuming caffeine or more than two consecutive days without caffeine.
The main result of the study was premature atrial contractions, but other interesting results were premature ventricular contractions, arrhythmias, the number of steps, the minutes of sleep and glucose levels. To measure these results, the participants were equipped with an electrocardiogram patch (ECG/EKG), an Activity Tracker (Fitbit) and a continuous glucose meter. The researchers took several measures to confirm compliance with the protocol; participants pressed a button on their ECG patch when consuming caffeinated coffee, in addition to filling out surveys, issuing receipts and downloading a geolocation application to confirm their presence in cafes. The characteristics of the participants are presented in Table.
