The Pros and Cons of Caffeine • Stronger by Science

Be aware: This text was the MASS Analysis Overview cowl story for February 2024 and is a assessment of a latest paper by Marcus et al. If you need extra content material like this, subscribe to MASS.

Key Factors

  • The current examine examined the consequences of acute caffeine consumption on cardiac arrhythmias, every day step counts, and sleep outcomes in 100 wholesome adults. 
  • Contributors took extra steps on espresso days (10,646 steps) than caffeine avoidance days (9665 steps). Nevertheless, caffeine additionally led to much less sleep (36 fewer minutes per night time) and extra every day untimely ventricular contractions (p < 0.05).
  • Caffeine isn’t inherently unhealthy or unhealthy, however we nonetheless don’t totally perceive its long-term impression on coaching variations and there are many people who find themselves higher off with out it. In the event you’re experiencing points that would probably be associated to caffeine (e.g., complications, poor sleep, anxiousness, and so forth.), experimenting with caffeine avoidance is likely to be worthwhile.

Caffeine is without doubt one of the few fitness-related matters the place the eagerness of health fans is matched, if not exceeded, by most of the people. The curiosity from lifters is comprehensible, as meta-analyses point out that caffeine can acutely improve quite a lot of efficiency outcomes together with power and energy (as coated on this MASS video). Curiosity from non-lifters is equally comprehensible, as everybody may use a morning increase of vitality and caffeinated drinks like tea and low play a distinguished position in lots of cultures. Roughly 85% of American adults eat a caffeinated beverage every day (2), and a few estimates place their common every day caffeine consumption simply north of 200 mg/day (3). Which may sound like rather a lot, however common every day caffeine intakes in Sweden and Finland exceed 400 mg/day (3). So far, one of many high highlights of my profession has been presenting at an unbelievable train science convention in Finland – having been there throughout a comparatively chilly month, I can vouch for the 400+ mg/day estimate. Espresso was just about all the time inside attain, and as a espresso lover, I used to be in heaven. 

Having mentioned that, many governments advise residents to restrict their every day caffeine consumption to not more than 300-400 mg/day, whereas some warning that every day intakes above 200 mg/day may result in undesirable unintended effects like nervousness or nervousness (4). Caffeinated drinks are additionally within the information after two latest lawsuits attributed deadly cardiac arrhythmias to the consumption of a selected product at an American restaurant chain. I wouldn’t dare get between a espresso drinker and their morning dose of caffeine, however we shouldn’t flip a blind eye to caffeine’s potential drawbacks simply because we take pleasure in its most fascinating traits. As a substitute, we should always seek the advice of the proof to find out if the professionals outweigh the cons, and that’s precisely what this text intends to do. Marcus et al (1) just lately examined the consequences of acute caffeine consumption on cardiac arrhythmias, every day step counts, and sleep outcomes, so let’s dive in and see what they discovered.

Function and Hypotheses


The aim of the presently reviewed examine was “to look at the consequences of caffeinated espresso on cardiac ectopy and arrhythmias, every day step counts, sleep minutes, and serum glucose ranges.”


The researchers didn’t explicitly state a speculation.

Topics and Strategies

The current examine screened 113 potential individuals and ended up enrolling 100 eligible adults who consumed caffeinated espresso a minimum of as soon as per yr. The researchers excluded individuals who had sure coronary heart circumstances, took sure drugs impacting coronary heart rhythms, or had a medical motive to keep away from espresso. The examine was a randomized crossover trial; individuals have been instructed to eat caffeinated espresso or keep away from caffeine in a collection of seven 2-day sequences (on-off or off-on), with the trial lasting 14 days in complete. Every morning, individuals obtained a textual content message informing them of their assigned situation (caffeinated espresso or no caffeine). These assignments have been despatched in a randomized order with two-day sequences to make sure that individuals would by no means go greater than two consecutive days with caffeine or greater than two consecutive days with out caffeine. 

The first examine consequence was untimely atrial contractions, however different outcomes of curiosity included untimely ventricular contractions, arrhythmias, step depend, sleep minutes, and glucose ranges. To measure these outcomes, individuals have been fitted with an electrocardiogram (ECG/EKG) patch, exercise tracker (Fitbit), and steady glucose monitor. The researchers took a number of steps to verify protocol adherence; individuals pressed a button on their ECG patch after they consumed caffeinated espresso, along with finishing surveys, offering receipts, and downloading a geolocation app to verify their presence in espresso outlets. Participant traits are introduced in Desk 1.

The Pros and Cons of Caffeine • Stronger by Science 11


Contributors had extra untimely atrial and ventricular contractions throughout espresso days than caffeine avoidance days. This was statistically important for untimely ventricular contractions (p < 0.05), however not for untimely atrial contractions (p = 0.10). These outcomes are introduced in Desk 2.

0224 Trexler Caffeine Table2
The Pros and Cons of Caffeine • Stronger by Science 12

Contributors took a mean of 1058 extra steps on espresso days compared to caffeine avoidance days. This distinction was statistically important (p < 0.05), with a 95% confidence interval starting from 441 to 1675. These information are introduced in Determine 1. 

0224 Trexler Caffeine Fig1
The Pros and Cons of Caffeine • Stronger by Science 13

Contributors received much less sleep on espresso days (for a complete of 397 minutes per night time) than on caffeine avoidance days (for a complete of 432 minutes per night time). This imply distinction of ~36 minutes was statistically important (p < 0.05), with a 95% confidence interval starting from 25 to 47 minutes. These information are introduced in Determine 2.

0224 Trexler Caffeine Fig2
The Pros and Cons of Caffeine • Stronger by Science 14

Common blood glucose ranges weren’t meaningfully impacted by espresso or caffeine avoidance. Common glucose ranges have been 95 mg/dL on espresso days and 96 mg/dL on caffeine avoidance days (imply distinction = -0.41 mg/dL; 95% CI, -5.42 to 4.60 mg/dL). In previous MASS articles (one, two), we’ve talked about how sure genotypes are related to quicker caffeine metabolism, whereas different genotypes are related to slower caffeine metabolism. Within the current examine, these genotypes didn’t have a constant impression on outcomes. Contributors with quicker genotypes tended to have extra untimely ventricular contractions on espresso days, whereas individuals with slower genotypes tended to expertise bigger sleep reductions on espresso days. In different phrases, there was a bent for quick metabolizers to have higher sleep-related outcomes, however worse heart-related outcomes. Genotype had just about no impression on step depend responses to caffeine.


We’ve introduced the case “for” caffeine on many events inside the pages of MASS, and it’s a simple case to make. At the beginning, individuals love caffeine and the drinks that carry it. Throughout quite a few nations, the overwhelming majority of adults eat caffeinated drinks regularly as a result of they love the beverage itself or take pleasure in a fast vitality increase. As well as, meta-analyses point out that acute caffeine consumption improves quite a lot of exercise-related outcomes together with endurance, power, and energy (5). On high of all that, the presently reviewed examine means that caffeine consumption can increase the quantity of bodily exercise you accrue all through the day, which is mostly favorable for health-related outcomes. Nonetheless, towards my higher judgment, my aim on this article is to current the case “towards” caffeine.

Many lifters and athletes refuse to entertain the concept of ditching caffeine as a result of they’re hesitant to forego the ergogenic (performance-enhancing) impact of caffeine consumption. Whereas that perspective is comprehensible, there are legitimate causes to problem (or a minimum of query) the premise. At the beginning, it’s necessary to acknowledge that caffeine’s results on power and energy outcomes are usually modest in magnitude, with meta-analyses reporting Cohen’s d impact sizes within the 0.1 to 0.3 vary (5). That’s a good impact measurement for a dietary complement (on condition that so few of them truly work), but it surely’s actually not going to make a game-changing impression in the long term. Talking of the long term, I’ve famous in a earlier MASS article that cross-sectional caffeine supplementation research report acute efficiency enhancements in ordinary caffeine customers (6). Nevertheless, there are only a few longitudinal research that really quantify caffeine’s performance-enhancing results over an prolonged timeline of repeated use. One such examine (7) was beforehand reviewed in MASS, and the outcomes hinted at lowered impact sizes over the course of 20 days. There’s additionally a obtrusive lack of research exploring the consequences of caffeine withdrawal on train efficiency. So, regardless of cross-sectional research reporting acute efficiency enhancement when ordinary caffeine customers eat pre-exercise caffeine (6), it’s usually troublesome to find out if caffeine is merely overcoming efficiency impairments induced by caffeine withdrawal signs. In such a state of affairs, caffeine can be restoring typical efficiency ranges moderately than elevating efficiency past a person’s typical degree. Based mostly on the dearth of direct proof associated to those issues, it’s laborious to definitively conclude that routinely supplementing with caffeine earlier than train will meaningfully increase efficiency in the long term.

On a associated observe, there are only a few research exploring power coaching variations in response to ordinary pre-exercise caffeine supplementation. Individuals usually assume that caffeine should facilitate higher coaching variations over time as a result of it acutely enhances efficiency. Whereas it’s intuitive to imagine that acutely enhancing coaching efficiency will inevitably result in higher coaching variations over time, that’s not all the time the case. Some of us draw conclusions about power caffeine consumption primarily based on multi-ingredient pre-workout complement research, however this can be a dangerous extrapolation to make. Pre-workout dietary supplements sometimes include caffeine at the side of a number of different ergogenic substances, which makes it troublesome to discern the consequences attributable to caffeine itself. We beforehand reviewed a examine (8) that straight investigated the consequences of normal caffeine supplementation on power coaching variations. Whereas the outcomes leaned very barely in favor of the caffeine group (in comparison with the placebo group), the findings weren’t statistically important. In abstract, we nonetheless don’t know if power pre-exercise caffeine supplementation truly improves coaching variations for lifters.

Whereas habituation is a crucial consideration for power caffeine use, sleep impairment is as effectively. Again in 2013, a examine by Drake and colleagues (9) sought to find out how the timing of caffeine consumption impacts sleep high quality. Contributors both consumed no caffeine or consumed 400mg of caffeine 0, 3, and 6 hours previous to mattress. Outcomes indicated that caffeine impaired sleep high quality in any respect time factors measured. Whereas that is usually misinterpreted as suggesting that you must cease consuming caffeine 6 hours earlier than mattress, the outcomes truly don’t assist us decide when the “preferrred” cut-off time can be. Figuring out that caffeine impairs sleep 6 hours earlier than mattress doesn’t give us any proof indicating that sleep is just not impaired when caffeine is consumed 7 hours earlier than mattress. As reviewed in a earlier concern of MASS, a latest meta-regression (10) supplies rather more sensible steering concerning caffeine timing. As you may count on, Gardiner and colleagues discovered that caffeine dose impacted caffeine timing close to sleep disruption. They concluded that you simply’d need to eat a 217.5mg dose a minimum of 13 hours earlier than mattress and a 107mg dose a minimum of 9 hours earlier than mattress, whereas smaller doses (<50mg) don’t appear to meaningfully impression sleep high quality. These findings are summarized in Determine 3. I consider it’s protected to imagine that these doses ought to be seen as cumulative in nature; you probably have 100mg at 9 a.m. and 100mg at 1 p.m., the “dose” at 1 p.m. can be higher than 100mg however decrease than 200mg, as solely a small portion of the 11 a.m. dose can be metabolized and cleared from the bloodstream by 1 p.m.

0224 Trexler Caffeine Fig3
The Pros and Cons of Caffeine • Stronger by Science 15

The presently reviewed examine discovered optimistic results on step counts, but it surely broadly reinforces considerations about caffeine consumption and sleep high quality impairment. Caffeine lovers usually downplay these considerations by leaning on considered one of two justifications: habituation or genotype. In the event you dig into the supplementary supplies of the current examine, you’ll discover partial assist for these justifications. For instance, some individuals counsel that they’re so habituated to caffeine’s wakefulness results that late-night caffeine consumption fails to impression their sleep. Within the current examine, individuals who usually consumed 1 or extra cups of espresso per day at baseline skilled a mean sleep discount of -28.9 minutes on caffeine days, whereas individuals who usually consumed lower than one cup per day skilled a mean sleep discount of -52.6 minutes. This will likely not directly counsel that every day caffeine consumption attenuates, however doesn’t eradicate, unfavorable impacts on sleep. As well as, some individuals counsel that they’re “immune” to caffeine’s results on sleep as a result of they’ve received the genotype related to quicker caffeine metabolism. Within the current examine, people with intermediate and gradual caffeine genotypes misplaced a mean of 34 and 47 minutes of sleep per night time (respectively) on caffeine days, whereas quick metabolizers skilled a imply improve of 33 minutes per night time. Nonetheless, I’m hesitant to conclude that the everyday individual can assume (hope) they’re a quick metabolizer and eat late-night caffeine with out sleep-related penalties for 2 causes. First, now we have inadequate details about how a lot caffeine these people consumed and what time of day they consumed it. Second, there have been solely 13 individuals with “quick” genotypes. This will increase the probability of a spurious discovering, and in addition means that the overwhelming majority of individuals on this examine (who’re, in idea, consultant of the inhabitants they have been sampled from) skilled worse sleep on caffeine days.

On the subject of the heart-related outcomes reported on this examine, I need to contextualize these a bit. I do know my aim on this article was to current a viable case towards caffeine, however I don’t need to current a hyperbolic or alarmist argument. In the event you’ve ever watched a TV present or film with a hospital scene, you’ve in all probability seen somebody hooked as much as a coronary heart monitor, also referred to as an EKG (elektrokardiogramm) or ECG (electrocardiogram). The traditional squiggly sample displays {the electrical} exercise of the guts, which dictates the coordinated rhythm and contraction of every heartbeat. The Q wave represents depolarization of the atrium, the QRS wave advanced represents the depolarization of the ventricle, and the T wave represents ventricular repolarization (you possibly can be taught extra about ECGs and coronary heart rhythms right here). After we discuss coronary heart arrhythmias, we’re speaking a couple of disruption within the typical rhythm of the guts. In lots of circumstances, arrhythmias are transient and benign (this examine noticed over 100 untimely ventricular contractions per day, on common), however they will generally result in probably life-threatening medical emergencies. 

In the event you comply with the information persistently, you generally come throughout shocking tales indicating that somebody died from a excessive, however not astronomically excessive, dose of caffeine (for instance, 400-800 mg or so). Mounting proof means that people with a coronary heart situation known as “lengthy QT syndrome” are significantly inclined to harmful arrhythmias in response to caffeine consumption (11). Lengthy QT syndrome is precisely what it feels like – people with this situation have a longer-than-average QT interval, which is the size of time between their Q wave and T wave. Caffeine might extend QT intervals, which will be harmful for individuals who have lengthy QT intervals to begin with (12). All of that’s to say, except we’re speaking about an unintended overdose from a misidentified powder or a totally reckless try to deliberately over-consume caffeine, caffeine is unlikely to induce clinically related or extreme coronary heart arrhythmias in in any other case wholesome people. Nevertheless, individuals with pre-existing coronary heart circumstances ought to seek the advice of with a certified clinician to find out a protected consumption vary for them.

To conclude this text, I need to share a quick anecdote. I’ve been a high-dose (≥400-500 mg per day) caffeine shopper for a few years, and I just lately stopped consuming caffeine solely. I used to be too sick to comfortably drink drinks for a couple of days, so I figured I’d do some experiment if I used to be going to expertise caffeine withdrawal both manner. I’ve been off of caffeine for a couple of month now, and my observations have been fairly fascinating. As somebody who is mostly vulnerable to anxiousness, I’ve seen a dramatic discount in anxiety-related signs. I used to get complications if I consumed too little caffeine, however I additionally received complications if I consumed an excessive amount of caffeine. For sure, that’s not an issue anymore. I additionally noticed that I really feel the necessity to nap extra – on the floor that appears too apparent to be insightful, however I’ve come to comprehend that I had been undersleeping to a a lot higher diploma than I spotted, and caffeine was overlaying that up like a Band-Help. 

When it comes to lifting efficiency, I haven’t seen something in any respect. At first it felt unusual to elevate weights and not using a pre-exercise dose of caffeine, however I’ve come to comprehend that this was extra associated to the ritual and subjective expertise of caffeination than anything. I eat caffeine earlier than exercises as a result of it’s what I’ve all the time executed (for a lot of, a few years). In consequence, I’ve subconsciously related the subjective feeling of “peak caffeination” as the sensation of being ready to elevate. This psychological hyperlink has traditionally led me to really feel unprepared to elevate once I’m not caffeinated, however pushing via uncaffeinated exercises has opened my eyes to the truth that caffeine wasn’t doing an excessive amount of for my exercises within the first place. 

We’ve bolstered the significance of sleep many instances in earlier MASS points, with analysis collectively indicating that ample sleep will be necessary for efficiency, physique composition, urge for food regulation, subjective wellness (usually feeling good), and quite a lot of different outcomes. We’ve additionally talked about the idea of expectancy results (one, two), like after we count on a placebo to have optimistic results or count on a nocebo to have unfavorable results. In my time away from caffeine, I’ve come to seek out that caffeine’s internet impression on my health progress was in all probability impartial at finest – the potential advantages, which can be inclined to a point of habituation, got here with the downside of insufficient sleep high quality. I’ve additionally noticed that most of the advantages I beforehand related to caffeine have been more than likely influenced by my expectations; I tended to overestimate caffeine’s optimistic results and exaggerate the hypothetical downsides of not consuming caffeine. A lot to the dismay of the high-powered advertising machine that dictates my each transfer, I’m not going to make the flashy declare that ditching caffeine will change your life, or that caffeine abstention is the one bizarre trick you’re lacking out on. Nevertheless, I might encourage you to ask your self a couple of questions: 

Do you’re feeling higher once you eat caffeine, or does caffeine allow you to keep away from unhealthy emotions (e.g., complications, drowsiness, and so forth.) which are attributable to caffeine within the first place? Are you truly sleeping effectively sufficient, or is caffeine masking the indicators of inadequate sleep? Does caffeine meaningfully enhance your efficiency, or have you ever come to count on poor efficiency once you’re not caffeinated? Do you have got any predispositions (e.g., nervousness, gradual caffeine metabolism, sleep points, coronary heart arrhythmias, or household historical past of coronary heart circumstances) that make you query your present degree of caffeine consumption?

Don’t get me incorrect – most individuals eat caffeinated drinks usually and tolerate them fairly effectively. They really feel nice, carry out effectively, and expertise completely no antagonistic outcomes associated to their caffeine consumption. Nevertheless, for some share of the human inhabitants, caffeine avoidance is likely to be preferable compared to common caffeine consumption. In different phrases, caffeine is completely wonderful for most individuals, but it surely’s not for everybody, and it’s not with out potential drawbacks. I by no means imagined I might say this, however I a lot choose the decaffeinated life primarily based on the way it makes me really feel on a day-to-day foundation. I really feel much less anxious, well-rested, and able to carry out (mentally and bodily) in any respect hours of the day, and I by no means discover myself feeling unprepared for a psychological, social, or bodily process as a result of I haven’t had my espresso but. 

However sufficient with the anecdotes – let’s wrap this up by summarizing the proof. Within the presently reviewed examine, caffeine was related to some execs and a few cons. On the intense facet, individuals have been extra bodily energetic and accrued extra steps per day on caffeine. Nevertheless, caffeine consumption led to sleep impairment and elevated frequency of coronary heart arrhythmias. Caffeine is just not inherently unhealthy for you, and most of the people will expertise no significant enhancements of their well being, wellness, or efficiency in the event that they cut back from two every day cups of espresso to zero. Nonetheless, you probably have been identified with a coronary heart situation (or suspect that you simply might need an undiagnosed coronary heart situation), you must verify with a certified healthcare skilled to completely discover the matter and decide an applicable caffeine consumption degree on your state of affairs. In the event you’re experiencing points that would probably be associated to caffeine (e.g., complications, poor sleep, anxiousness, and so forth.), or when you’re merely getting manner out of hand along with your every day caffeine dosage, it is likely to be time to ask your self the questions listed on this article to find out if a caffeine-free experiment is a worthwhile pursuit.

Subsequent Steps

Surprisingly sufficient, we nonetheless have rather a lot to find out about caffeine. I’d prefer to see extra experimental analysis pertaining to how completely different caffeine doses and timing methods impression sleep, and the way we are able to clarify completely different subjective experiences (i.e., some individuals counsel that caffeine has no impression on their sleep, whereas others report being extremely delicate to it). I’m significantly excited by discovering out if these divergent impacts on subjective sleep high quality are associated to charge of caffeine metabolism, habituation amongst common caffeine customers, inaccurate self-assessments of sleep high quality, or one thing else solely. On the health facet of issues, I feel we want a couple of longitudinal research to look at how caffeine’s results on power and energy change over time and the way caffeine withdrawal impacts train efficiency. A majority of these research can be good for a grasp’s-level thesis undertaking or as a part of a multi-study doctoral dissertation – they tackle a simple query and might be accomplished with very modest budgets and comparatively quick examine timelines. Lastly, it’d be nice to see extra longitudinal research that really quantify caffeine’s results on power coaching variations moderately than acute efficiency metrics.

Software and Takeaways

Caffeine acutely improves efficiency and will passively result in larger bodily exercise ranges. Nevertheless, caffeine can impair sleep, and its results on long-term coaching variations are presently unsure. As well as, caffeine can worsen nervousness signs and result in clinically related arrhythmias in individuals with pre-existing coronary heart circumstances. Caffeine isn’t inherently unhealthy, but it surely’s not for everyone. Caffeine consumption habits ought to be individualized to suit your targets, preferences, subjective experiences, and medical issues.

This text was the duvet story for the February 2024 concern of MASS Analysis Overview. In the event you’d prefer to learn the total, 93-page publication (and dive into the MASS archives), you possibly can subscribe to MASS right here.

Subscribers get a brand new version of MASS every month. Every concern consists of analysis assessment articles, video shows, and audio summaries. PDF points are normally round 100 pages lengthy.


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