Hey, and welcome to my science based guide to the benefits and side effects of caffeine.
I've written this guide to give caffeine a fair trial - by taking a closer look at the science behind both its (potential) benefits and (potential) negative side effects.
So use this guide as a good starting point if you're deciding whether or not you should start taking caffeine - or whether or not you should ultimately ditch your caffeine habit.
But I can promise you one thing...if you read this guide all the way through, you'll understand caffeine a lot better than 99% of people on this planet.
From the effects of caffeine on your brain (mental performance) to how it can boost your capacity for exercise (sports performance).
From positive effects on some health conditions (diabetes, dementia...) to the negative effects of dehydration and straight up overdosing on caffeine.
This guide has you covered...plus, everything I claim in this guide is based on hardcore science.
But before we dive in, here's a short roadmap of my thorough guide on caffeine (use it to quickly navigate this guide).
When it comes to caffeine's effect on your brain and mental performance, many benefits have already been proven by modern science.
From making it a little easier for you to solve complex (math) problems, to boosting your memory, wakefulness, and alertness.
Also, caffeine isn't only an awesome way to jump-start your day, but as you'll see, science has proven that it can actually improve your mood and happiness.
Let's dive right in.
Logical thinking and problem solving
Studies have proven that caffeine improves your problem solving skills  and boosts your logical thinking .
It also increases your ability to solve math problems  and helps you process information at higher speeds .
In other words, if you're facing a tough exam, a challenging meeting, or trying to organize a complex event/party, normal doses of caffeine can help you cope with the insanity.
Also, on days when you feel fully rested and energized, you won't need as much caffeine as on days when you feel tired or sleepy (to get the same performance boost) (21).
But there's more to it.
Taking too much caffeine can actually put the brakes on your mental abilities.
So, if you feel your mental performance is starting to drop (because you already took too much caffeine), the only smart thing you can do is stop taking it.
Getting in more caffeine at this point will only make things worse (22).
Science has proven that caffeine can improve your memory as well. It works for delayed recall (17), recognition memory (23), semantic memory (24), and verbal memory (25).
Caffeine has also been proven to boost your memory performance on both easy (26) and difficult (27) memory tasks.
If, for example, you have to study for an exam, memorize a speech, or just learn a couple of quotes by heart, taking caffeine before your challenge could really speed things up.
But there's a catch.
If you need to memorize a lot of complex and difficult stuff (think learning Latin words for different muscles), then taking too much caffeine could actually backfire (your memory performance could start to drop) (24).
In other words, if you've already taken a lot of caffeine and you get the feeling it's becoming harder and harder to memorize things, you should stop taking caffeine.
Taking even more caffeine at this point, could easily make things worse (28).
Alertness and wakefulness
Millions of coffee lovers worldwide rely on their morning cup of coffee to get them out of bed in the morning.
And the fact that caffeine can boost your wakefulness is more than just a popular rumor, science (29) has proven this to be true a long time ago.
Another study (21) has shown that caffeine isn't just some mild stimulant, it can help you even if you're suffering from a severe lack of sleep.
Many other studies (30) have also shown that caffeine can boost your alertness.
If you are facing a long study night or need to drive in the wee hours, caffeine can help you out to a degree.
But you have to be careful about not getting in too much caffeine.
While normal doses of caffeine boost your alertness and wakefulness, higher doses can actually make you feel less alert and sleepier (31).
Mood and happiness
Studies (32) have proven that caffeine can cheer you up and make you feel happier.
Caffeine can also boost your experience of pleasure (17), and even trigger euphoria-like feelings in some cases (33).
But again, this only works up to a point.
While normal doses of caffeine can make you feel better, taking too much caffeine can easily backfire.
Higher doses of caffeine have been proven to increase tension, anxiety, frustration, irritability, and nervousness (27).
So, depending on how sensitive you're to caffeine, too much caffeine could have a negative effect on your mood and happiness.
If you're in a negative mood, but haven't gotten any caffeine for the day, then taking caffeine might boost your happiness.
But if you feel nervous, frustrated, or in a bad mood after already drinking down a few cups of coffee, then taking even more caffeine could make things worse.
Plenty of science has already been done on caffeine and sports performance.
In general, there are two basic types of exercise or sports-like activities.
The first type is cardio exercise, where you perform some activity for a long time, while keeping your heart rate and breathing elevated. Think running, swimming, cycling, jogging, even walking...
The second type of exercise is strength training. With this type of exercise, you generally keep your heart rate low (while moving around heavy stuff). Think weight lifting, body weight exercise, strength training.
The reason why this matters, is because caffeine works differently with these two kinds of exercise.
Cardio exercise (low intensity)
First, let's take a look at low intensity cardio.
In one of the more popular studies (34) on caffeine and low intensity cardio, competitive cyclists took caffeine before a training session.
Caffeine allowed the athletes in the study to cycle longer, to burn off more calories from their body fat stores, and to feel less tired throughout the workout.
In another study (35) on caffeine and sports performance, caffeine was proven not only to help you exercise longer, but also at a higher intensity.
In other words, caffeine can help you train longer, go harder, and/or feel exhausted later than you normally would (36).
Cardio exercise (high intensity)
In one study (37), caffeine boosted the maximum swimming speed of highly trained swimmers. In another study (38), caffeine increased the maximum power in cycle sprinting.
Science (39) has also proven that caffeine can help athletes run faster (plus, it increased the speed of the "finishing burst" at the end of a run).
One more study (40) has proven that caffeine can boost the performance during high-intensity cycling.
So, if you're training/competing in a high-intensity sport (think sprinting, competitive cycling, HIIT, CrossFit or any similar high-intensity workout), caffeine could take your performance to the next level.
While the fact that caffeine boosts your ability for cardio exercise has long been proven by science (41), more research is needed on specific conditions under which caffeine boosts your strength.
Some studies (42; 43; 44) have shown no effect of caffeine on strength. But on the other hand, research has connected caffeine with increased "twitch tension", muscle contractility, and production of muscular force (45).
In one study (46), they showed caffeine boosts your strength if your muscles are already tired.
In another study (47), 20 strength-trained athletes were able to increase the strength and power output of their muscles with caffeine.
As far as current research goes, caffeine definitely has the potential to boost your strength and power, except it isn't yet 100% clear under what circumstances it actually works.
Switch to body fat as the primary source of fuel
You've already seen the science on how caffeine can release more energy (calories) from your body fat reserves in the chapter on using caffeine for fat burn.
(Caffeine has also been proven (46) to slow down the storage of body fat - but you can read more about how to use caffeine to get rid of that stubborn belly fat in my science based guide to taking caffeine for weight loss).
But this release of extra energy can be helpful with sports performance as well.
In one study (48), caffeine helped runners burn away more body fat. In another study (49), people took caffeine before exercise and again, caffeine was able to boost the release of calories from their body fat reserves during exercise.
But how does this help with sports performance?
Because caffeine releases some extra calories from your body fat reserves during exercise (and slows down the storage of body fat), your body will have more energy available to fuel your workouts.
This makes caffeine a zero-calorie source of energy, which means that you can exercise longer and/or harder with it (and generally feel less exhausted after your workouts).
Which brings us right to the next benefit of taking caffeine for sports performance...
Spare 42% of energy stored in your muscles (glycogen)
Glycogen is a primary source of energy your body relies upon during endurance exercise.
Glycogen is stored in your liver and your muscles, and once you wipe out your glycogen reserves (with an intense 2-hour run, for example), you won't be able to keep going.
Caffeine has been proven (36) to help your body spare glycogen during a workout. In fact, the people in that study burned away 42% less glycogen during exercise with caffeine.
So there you go. Because caffeine releases more fat-calories from your body fat reserves, your body has more energy available, which in turn helps you burn off less glycogen during exercise (50).
Reduce tiredness and muscle pain by up to 48%
If you burn away more fat calories during exercise, this means you will be less tired after a workout (because more energy will be drawn from your body fat reserves and less from your muscles).
In one study (51), cyclists were tested during a workout with or without caffeine. With caffeine, they were able to exercise harder without feeling any more tired.
In other words, caffeine can help you put in more effort without making you feel more tired (or put in the same effort while feeling less tired).
In another study (52), moderate doses of caffeine (about two cups of coffee) have been proven to help reduce muscle pain and soreness by up to 48%.
TIP: Take caffeine before a workout (to reduce the pain and soreness in your muscles after the workout), this could help you exercise more often, train harder, and recover faster between your workouts.
The benefit of staying away from caffeine for at least 4 days
There's one more thing you need to know if you really want to get the absolute maximum performance boost from caffeine.
Research has proven that people, who aren't used to caffeine, get a bigger sports performance boost (53) and better release more energy from their body fat reserves (54), than people who regularly take caffeine.
But here's what you can do to really maximize that benefits of caffeine for sports performance:
TIP: If you have a race or any major event where you really need to get the absolute best result, you'd do well to stay away from caffeine for at least 4 days (55) before the event where you really need to perform at your maximum.
Four days are more than enough for your body to get used to living without caffeine, and receive a much bigger boost from caffeine on "race day".
If you really want to challenge yourself (to break a personal record, for example), then you'll love this next benefit of caffeine for sports performance:
A psychological edge or a performance boost?
Caffeine has also been proven by many studies (34; 36; 53; 51) to give you a certain "psychological edge" when it comes to exercising.
And even though caffeine will only work on your mind (and not your body), your workouts will still feel easier, you'll feel less tired, and you'll be able to keep going longer and/or faster.
And this brings us right to the single major issue researchers looking into caffeine and sports performance are facing - the fact that it's pretty much impossible to separate between actual performance boosts (increases in strength and power) and the psychological effects.
TIP: With a long and tough day behind you, caffeine could tip the scales in your favor and help you actually drag yourself to the gym (even though you'd feel way too tired to do it without caffeine).
Caffeine can also make it a little easier on you to give 100% during the workout (even though you'd normally slack off).
Carbs may numb the effect of caffeine
Some research (56) has discovered that taking caffeine while on a high-carbohydrate diet can numb the boost caffeine normally provides to your ability to perform cardio exercise.
If you're an endurance athlete who's usually on a high-carb diet, this could be a bit of bad news for you. But on the other hand, some research has shown that carbohydrates do not negate the effects of caffeine (57).
The bottom line is, carbs may or may not reduce the effect of caffeine, but your best bet would be to avoid carbs as much as possible.
If you're facing a 3-hour marathon, then avoiding carbs may not be a good idea. In this case, just eat your carbs, take your caffeine, and hope for the best.
But if you're about to do a light, 45-minute jog, then get your pre-workout caffeine in before exercise without anything else (or at least go as low in carbs as possible, or better yes, stick to protein/fats).
Leave the carbs for your post-workout meal to make sure you get the biggest performance boost from caffeine, while ensuring fast recovery because you're having carbs right after exercise.
Time to take a look at the negative side of caffeine.
Negative side effects
Anyone can tell you at least one negative side effect of caffeine.
(Aka, how they couldn't live without their morning cup of coffee.)
But especially people who are into sports, have usually heard more than that.
Some of those are myth and some of those are fact.
So let's see what science has to say about the single most common (potential) side effect of caffeine:
Lots of people have been taught to believe that coffee, or more precisely, caffeine, can cause dehydration.
And it's true. If you take really high doses of caffeine (think 7+ cups of coffee), you could lose a pound or two of water weight pretty quickly (58).
But in normal doses (2-3 cups of coffee), caffeine simply won't be powerful enough to help you get rid of any extra water weight (59).
In fact, science has proven that even if you lose a lot of body water with exercise, caffeine still can't dehydrate you (60).
So there you go.
While it's possible to get rid of some water weight with caffeine, it can only do it with dangerously high doses.
In a rare and pretty extreme case of caffeine overdose (5), a woman suffered from health problems like low-grade fever, insomnia, anorexia, and irritability.
This happened because she was (unknowingly) getting in about 1,500-1,800 mg of caffeine per day.
And even though her problems were annoying, they were quickly gone, as soon as she stopped getting in as much caffeine.
That being said, it is actually possible to overdose on caffeine, but only if you consume mega-doses of over 10,000 milligrams (6).
In other words, you would have to drink around 100 cups of coffee for caffeine to become toxic in your body.
I'm counting on you not to do that.
Because caffeine is a stimulant, if you are pregnant or nursing, you should consult with your doctor if it's safe for you to touch caffeine at all.
Studies (62; 63; 64) have shown that drinking too much caffeine during pregnancy increases the risk of miscarriage.
So, it's recommend to pregnant women that at the very least, they reduce their caffeine intake during pregnancy.
Another credible medical authority, Mayo Clinic (2) recommend limiting the amount of caffeine to less than 200 milligrams a day during pregnancy.
With that out of the way, let's get on with some more amazing health benefits of caffeine.
As if all the amazing benefits of caffeine for sports and mental performance, weren't enough...
...science has also confirmed quite a few other health benefits of caffeine.
So let's take a look at the science behind some of those:
Caffeine boosts the levels of the so-called happiness hormone (dopamine) in your body.
One study has shown (75) that caffeine increases levels of dopamine in the brain, which tends to enhance concentration, boost mood and produces a positive state of mind.
High dopamine levels help you feel more energetic, boost your performance, and helps you focus.
This may actually boost your ability to learn new things.
People with high dopamine may be more productive than everyone else.
Also, high levels of dopamine may produce a greater sense of self-control.
Lowers your blood glucose
One study (74) has shown that caffeine can help people who suffer from type 2 diabetes.
People who take caffeine regularly, (and for a longer period of time), brought down their blood glucose levels.
So if you're on a diet or exercise program because of high blood sugar, then throwing in some caffeine could help you bring things under control.
Warning: If you are taking insulin, your blood sugar can actually drop too low - always discuss anything you might read on ANY website with your doctor.
Dementia and Alzheimer's disease.
Caffeine has been proven to "partially reverse age-related deficits in cognitive functioning" (48).
Quite a few studies have shown that getting in moderate amounts of caffeine (three to five cups of coffee per day) at mid-life is linked to a reduced risk of dementia in late life.
Dementia and Alzheimer's disease are two of the most rapidly increasing public health problems in ageing populations - with no immediate cure in sight.
One study (61) has shown that drinking 3-5 cups of coffee per day decreased risk of dementia by 65%.
But you should know that caffeinated soft drinks with caffeine added to them, do not deliver these benefits...
...because they lack the antioxidants that you get if you drink down caffeine as coffee or tea.
How much caffeine should you take per day?
According to the U.S. Food and Drug Administration, some doctors suggest we should consume between 100 and 200 milligrams (mg) of caffeine a day (1).
Another credible medical authority, Mayo Clinic, says that consuming up to 400 milligrams (mg) of caffeine per day should be safe for most healthy adults (2).
In one review of scientific studies on caffeine, the researchers concluded that daily doses of up to 400 mg seem to maximize the benefits of caffeine (while minimizing its risks) (3).
Depending on your size, gender, and sensitivity to caffeine, you could get away with doses higher than 400 mg, but most experts agree that 600 mg of caffeine a day is too much (1).
So, if you're a healthy adult with no medical issues (only your own doctor can confirm this for you), you should be able to safely consume 300mg-400mg of caffeine per day without any negative side effects (4).
Here's a short recap of this thorough, science based guide to the benefits and side effects of caffeine:
- Caffeine can have a profound effect on your brain and mental performance. It can boost your memory, your logical thinking and problem solving abilities, and make you more alert and awake. Possibly, it can even improve your mood.
- Caffeine can boost your sports/exercise performance - both for strength training and cardio exercise. The major benefits of caffeine in this area are: you can train longer, go harder and feel less exhausted after a workout.
- The negative side effects of caffeine don't seem that awful on the surface (it's quite tough to both dehydrate yourself and overdose on caffeine).
- Beyond sports and mental performance, some positive effects of caffeine have been confirmed for depression, high blood sugar, dementia and Alzheimer's disease.
- Several different sources confirm that you'd do best to take between 200 and 400 milligrams of caffeine per day (and do your best not to go above 600). Unless you're pregnant, in which case you'd do best to avoid caffeine altogether.
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