Is Caffeine Bad For You?

A cup of coffee with coffee beans on a table

If your day hasn’t officially started until you’ve got some caffeine buzzing through your veins, you are definitely not alone. Caffeine is the most widely used stimulant in the world, which means that everyone from sleep-deprived college students to top-level execs depends on a cup of joe or an energy drink to get them ready to face the day.

Caffeine is also a popular supplement ingredient among athletes and fitness enthusiasts since it can give you the focus and edge you need to get a great workout. So, caffeine can also be found in gym bags everywhere, added to pre-workout formulas and other sports nutrition supplements.

However, caffeine is first and foremost a drug, which means that some people may have questions about whether or not their caffeine usage is safe and healthy.

So, the question we need to address is whether caffeine is bad for you or not? If so, how much caffeine is dangerous? Let’s talk about it!

How caffeine works

Caffeine is considered a psychoactive drug since it can actively stimulate your central nervous system. At its most technical definition, caffeine is an adenosine receptor antagonist.^[1]

Let’s quickly explain what this means.

Adenosine is a neurotransmitter, which are chemicals that act on your nervous system. These neurotransmitters have unique receptors in your brain, and once they make contact they can carry out their “duties.” Adenosine has a depressant effect on your central nervous system when it reaches its intended receptors and is therefore associated with drowsiness.

But when you ingest caffeine, it can latch on to those same receptors that adenosine would, effectively blocking it and preventing adenosine from binding. The result? You feel more alert and energized than you otherwise would if adenosine levels were allowed to increase.

Where is caffeine found?

Caffeine can be found in varying amounts in a variety of foods and beverages. Some of the most popular places you can find caffeine include:

Coffee
Tea
Soda
Energy drinks
Pre-workout supplements
Chocolate

You might also find moderate amounts of caffeine in certain medications like decongestants and bronchodilators.

Caffeine Benefits

The increase in alertness and focus that caffeine provides has many merits, the most obvious being that it can keep you energized and focused enough to tackle whatever happens to be on your agenda for the day.

As it turns out, though, some of the key benefits of caffeine really start to shine when it comes to fitness and athletic performance. Athletes and gymgoers often use caffeine before a workout as an ergogenic aid^[2] to boost their energy levels and athletic performance, hence why you’re likely to find caffeine listed as an ingredient in many pre-workouts. It’s also thought to moderately decrease your body’s dependence on glycogen^[3] and increase its dependence on free fatty acid mobilization.

It also goes far beyond keeping you focused and fueled during your lifts. Key benefits of using caffeine before workout:

Performance - There’s evidence to suggest that caffeine can be an effective aid for increasing maximal strength, muscular endurance, and power,^[4] which is great news for anyone who includes resistance training in their fitness regimen! For example, a study^[5] found that pre-workout caffeine was able to improve muscle adaptations during bench press exercises, which translated to increased velocity and power on the bench when compared to a placebo group.
Endurance - Caffeine is also thought to decrease pain perception, which can translate into a longer workout for you. Researchers have found that caffeine supplementation during high-intensity workouts can lead to an increase in beta-endorphin concentration in the blood,^[3] and these neurotransmitters can then alleviate some of the pain you might otherwise feel during a workout.

In addition to its ability to help you smash your workout, some caffeinated drinks are thought to have some pretty impressive long-term health benefits as well. An umbrella review^[6] that evaluated a total of 201 meta-analyses on the effects of coffee consumption on health outcomes found that moderate to high levels of coffee consumption (about 3-5 cups/day) was associated with:

19% decreased risk for mortality from cardiovascular disease, 16% risk of mortality from coronary heart disease, and 30% risk of mortality from stroke
Lowered risk of various cancers, including prostate, endometrial, melanoma, leukemia, and liver cancers, when compared to low coffee consumption
Lower risk for various liver health outcomes like liver fibrosis, liver cirrhosis, and non-alcoholic fatty liver disease
Lower risk of type 2 diabetes
And an overall lowered risk of all-cause mortality

Is caffeine dangerous?

So even though caffeine consumption has been shown time and time again to come with many benefits both inside and outside of the gym, contradicting evidence about the dangers of caffeine consumption can still leave some consumers confused. Why is this?

The answer is not entirely black-and-white here, and there are many different factors that can determine how much caffeine is a “healthy amount” for each individual. Ultimately, this gap is likely due to the fact that everyone has a slightly different response to caffeine.

For example, your genetics seems to play a pretty big role in how well your body can metabolize caffeine, and this can then go on to influence how much caffeine is a “safe” amount for you personally.

A great example of this is the issue of caffeine consumption and heart health. As we’ve already discussed, several meta-analyses have found an association between lowered cardiovascular health risks and moderate to high caffeine consumption. But caffeine is also sometimes associated with heart attacks in some coffee drinkers! These seemingly contradictory facts seem to come down to genetic differences in your cytochrome P450 system.

To put it simply:

The cytochrome P450 system is a set of enzymes in your liver that is responsible for metabolizing and breaking down drugs.
The main set of enzymes that break down caffeine is called CYP1A2. Your unique genetics can influence much of the activity^[7] carried out by the CYP1A2 enzymes, as can some other lifestyle factors like smoking and the use of oral contraceptives.
These genetic and environmental differences mean that people can metabolize caffeine at different speeds. Some people are “fast” metabolizers, others are “slow” metabolizers, and there are plenty more in between on the spectrum.

Since everyone metabolizes caffeine at a different rate, this can influence how caffeine can impact an individual’s health. To illustrate this point, one study^[8] found that coffee intake was associated with increased risks of nonfatal heart attacks, but only with people who were “slow” caffeine metabolizers as evidenced by genotyping.

There’s also the issue of how caffeine may affect bone density, especially in populations who are more at risk of bone fractures and/or calcium deficiencies.^[9] Caffeine consumption is thought to inhibit the absorption of calcium^[10] from your diet, which is an important structural component of strong and healthy bones. While there isn’t strong conclusive clinical evidence to show that caffeine can increase your risk of osteoporosis or other bone diseases, there is mechanistic data to suggest this, so it’s worth keeping in mind if you’re at a higher risk of bone fractures.

Ultimately, caffeine in and of itself isn’t a bad thing … and as we’ve already talked about, a moderate amount of caffeine can actually be pretty good for your health in the long run! But still, genetic and lifestyle differences can skew your individual tolerance and metabolism of caffeine, which means that the risks that come with caffeine consumption can vary from person to person.

Some Universal Issues: Doses and Caffeine Dependency

There’s still more work to be done to really understand what these genetic differences mean for caffeine drinkers and their long-term health. But what we do know right now is that the dose always matters.

So how much caffeine is dangerous?

Like almost any other substance, the difference between a healthy caffeine intake and a dangerous one ultimately comes down to the amount that you are drinking. Lethal caffeine overdoses are possible, even if they’re fairly rare: a lethal blood level of caffeine seems to be somewhere above 80-100 mg per liter of blood.^[11] While everyone’s caffeine tolerance is different, the LD50, or the lethal dose for 50% of the population, is thought to be about 150-200 mg per kilogram^[12] of your body weight. That's over 10,000mg of caffeine for a 150lb person. To put that into perspective, a double shot of espresso contains only about 150 mg of caffeine.

Caffeine is also absorbed by your body pretty quickly, which means that the consumption of this caffeine would need to be pretty rapid (but again, keep in mind that some people are genetically predisposed to be more sensitive to caffeine)

What this means is that you would have to drink a huge amount of caffeine at one time to be in any real danger of an immediate health risk.

But barring immediate health dangers, there are also other potential negative side effects you might experience when drinking caffeine. Intaking a high dose of caffeine may not be dangerous, per se, but it can come with side effects like jitters, anxiety, nausea, gastrointestinal issues, and insomnia, especially among people who are more sensitive to caffeine.

One of the most pressing issues here, though, is that habitual caffeine consumption can lead to caffeine dependence. After all, caffeine is first and foremost a drug. It can be habit-forming, as anyone who needs their daily caffeine fix can attest to. A caffeine use disorder^[13] can come with the markings of many other drug habits, including increased tolerance (and increased use as a result), and unpleasant withdrawal symptoms if you try to cut your use.

What is a healthy amount of caffeine, then?

Again, a healthy caffeine intake can vary from person to person.

In general terms, the FDA recommends no more than 400 mg of caffeine per day, or the equivalent of roughly four cups of coffee, for healthy adults.^[14] For comparison’s sake, one study estimated that about 85% of Americans have at least one caffeinated beverage per day, with a mean daily intake of about 165 mg.^[15]

The Bottom Line On Caffeine

Many of us depend on caffeine to perform at our best, whether it’s at work or in the gym. For the most part, caffeine in and of itself is not dangerous, and can actually be pretty good for your health in moderate doses. However, certain factors like your genetics, inherent sensitivity, and daily dosage can present their own share of issues.

So yes, your pre-workout probably isn’t a huge issue, but be sure to use it responsibly if you really want to make the most out of its energy-boosting benefits.

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References

1. Daly, John W et al. “The role of adenosine receptors in the central action of caffeine.” Pharmacopsychoecologia vol. 7,2 (1994): 201-213.

2. Pickering, Craig, and Jozo Grgic. “Caffeine and Exercise: What Next?.” Sports medicine (Auckland, N.Z.) vol. 49,7 (2019): 1007-1030. doi:10.1007/s40279-019-01101-0

3. Goldstein, E.R., Ziegenfuss, T., Kalman, D. et al. International society of sports nutrition position stand: caffeine and performance. J Int Soc Sports Nutr 7, 5 (2010). https://doi.org/10.1186/1550-2783-7-5

4. Grgic J. Effects of Caffeine on Resistance Exercise: A Review of Recent Research. Sports Med. 2021 Nov;51(11):2281-2298. doi: 10.1007/s40279-021-01521-x. Epub 2021 Jul 22. PMID: 34291426.

5. Giráldez-Costas V, Ruíz-Moreno C, González-García J, Lara B, Del Coso J and Salinero JJ (2021) Pre-exercise Caffeine Intake Enhances Bench Press Strength Training Adaptations. Front. Nutr. 8:622564. doi: 10.3389/fnut.2021.622564

6. Poole, Robin et al. “Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes.” BMJ (Clinical research ed.) vol. 359 j5024. 22 Nov. 2017, doi:10.1136/bmj.j5024

7. Rasmussen BB, Brix TH, Kyvik KO, Brøsen K. The interindividual differences in the 3-demthylation of caffeine alias CYP1A2 is determined by both genetic and environmental factors. Pharmacogenetics. 2002 Aug;12(6):473-8. doi: 10.1097/00008571-200208000-00008. PMID: 12172216.

8. Cornelis MC, El-Sohemy A, Kabagambe EK, Campos H. Coffee, CYP1A2 genotype, and risk of myocardial infarction. JAMA. 2006 Mar 8;295(10):1135-41. doi: 10.1001/jama.295.10.1135. PMID: 16522833.

9. Heaney RP. Effects of caffeine on bone and the calcium economy. Food Chem Toxicol. 2002 Sep;40(9):1263-70. doi: 10.1016/s0278-6915(02)00094-7. PMID: 12204390.

10. Berman NK, Honig S, Cronstein BN, Pillinger MH. The effects of caffeine on bone mineral density and fracture risk. Osteoporos Int. 2022 Jun;33(6):1235-1241. doi: 10.1007/s00198-021-05972-w. Epub 2022 Jan 4. PMID: 34981132.

11. Murray A, Traylor J. Caffeine Toxicity. [Updated 2023 Jun 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532910/

12. Peters, J. Factors Affecting Caffeine Toxicity: A Review of the Literature. https://doi.org/10.1002/j.1552-4604.1967.tb00034.x

13. Meredith, Steven E et al. “Caffeine Use Disorder: A Comprehensive Review and Research Agenda.” Journal of caffeine research vol. 3,3 (2013): 114-130. doi:10.1089/jcr.2013.0016

14. Spilling the Beans: How Much Caffeine is Too Much? US Food & Drug Administration.

15. Mitchell DC, Knight CA, Hockenberry J, Teplansky R, Hartman TJ. Beverage caffeine intakes in the U.S. Food Chem Toxicol. 2014 Jan;63:136-42. doi: 10.1016/j.fct.2013.10.042. Epub 2013 Nov 1. PMID: 24189158.