Caffeine is one of the most popular stimulants in the world. A majority of people drink it in a beverage form, such as coffee, tea or energy drinks. Caffeine creates a state of mental alertness and readiness that may enhance your workout performance. This effect may slightly improve your workout performance and muscle growth, but research into the topic is not conclusive.
Central Nervous System
The primary effect that caffeine has is on your central nervous system. The drug increases the firing of your neurons and triggers your pituitary gland to release adrenaline. American Council on Exercise sports nutritionist Fabio Comana states that reputable studies have shown this stimulating effect to improve endurance exercise performance. By allowing you to perform an exercise for longer periods of time and a sustained intensity level, caffeine may aid in muscle growth.
Fatty Acid Release
A second mechanism through which caffeine may enhance your muscle growth is through the release of fatty acids into your bloodstream. In a review of energy beverages presented in 2010 in the “Mayo Clinic Proceedings,” Dr. John Higgins and colleagues noted that your muscles will use fatty acids as an energy source before the stored glycogen in your muscles. Preserving your muscle glycogen may help you exercise for longer periods of time without reaching muscle exhaustion.
Short Term Exercise
Though caffeine may aid your workout performance in moderate intensity exercise over a long period of time, short-term, high-intensity exercise may not derive any benefits from caffeine consumption. This is because the primary energy source for short-term, high-intensity exercise like powerlifting is adenosine triphosphate or ATP. Released fatty acids from caffeine consumption do not serve as a replacement for ATP during this type of exercise. (1)
How does caffeine affect endurance?
When you exercise, your body uses glycogen, a type of sugar that you get from food, for energy. But once those stores are depleted at the end of a long workout, you may feel tired or sluggish—signs that you have “hit the wall.” Caffeine slows the depletion of glycogen by encouraging the body to use more fat as fuel, which helps to conserve energy over long periods of time. (2)
For this reason, sports that deplete a lot of glycogen, specifically endurance events, benefit the most from caffeine consumption. Activities lasting longer than an hour with sustained efforts, such as running, cycling, and cross-country skiing, all benefit from caffeine supplementation by allowing athletes to increase their endurance, accuracy, and speed. Conversely, caffeine provides no tangible benefits for strength and power activities, such as weight-lifting.
How does caffeine affect cognitive function?
Since caffeine enters almost all bodily tissues, it affects your nervous system and your brain. Caffeine acts as a stimulant and wakes you up, which means that when you consume it, you will feel more alert and react faster.
Drinking caffeine prior to physical exertion might actually help reduce the perception of pain. According to a study published by the department of kinesiology at the University of Illinois, people who drank caffeine experienced less anxiety associated with strenuous exercise, which may account for their lower perception of pain. For example, if you’ve ever felt your muscles burn during intense exercise, consuming caffeine before you start your workout may dull this sensation. (3)
How does caffeine affect hydration?
To maintain peak performance, you have to stay hydrated. Water regulates your body temperature, lubricates your joints, and transports nutrients throughout your body. Staying hydrated is particularly important during exercise because you lose water through sweat. The longer and more intensely you work out, the more necessary it becomes to get fluid into your body. When you don’t replenish your fluids, it becomes harder for your heart to circulate blood. A decrease in blood and plasma volume can contribute to muscle cramps, dizziness, fatigue, heat stroke, and heat exhaustion.
We’ve all heard the warning that caffeine has a diuretic effect and dehydrates you. However, research shows that this widely-held assumption is actually not true unless you consume a large amount of caffeine. Caffeine does not dehydrate you unless you drink more than 500-600 milligrams (the equivalent of 5-7 cups of coffee) per day. Below this level, your body does not lose any more fluid than the beverage itself provides. For comparison, an 8-ounce cup of coffee has about 100 milligrams of caffeine, and an energy drink can have as much as 242 milligrams per serving (though caffeine content varies between energy drink varieties). While caffeine may cause a little more fluid to be excreted as urine in a 24-hour period when compared to plain water, this effect is fairly mild and does not affect hydration. For anyone who loves coffee, the good news is that caffeinated beverages actually provide a sufficient amount of fluid for rehydration, even among people who exercise regularly in hot, humid conditions.
Although caffeine does not appear to have a significant impact on hydration, it can have other effects on your kidneys. One particular study has shown that caffeine can cause increased excretion of sodium from your body, but this usually does not cause problems in normal, healthy adults. However, the salt balance in your body can affect certain medications, so talk to your doctor if you have any questions about any medications that you are taking.
What’s more, individuals who aren’t used to caffeine may experience symptoms after consuming what is typically considered a moderate dose (4
Here are 8 side effects of too much caffeine.
Caffeine is known to increase alertness.
It works by blocking the effects of adenosine, a brain chemical that makes you feel tired. At the same time, it triggers the release of adrenaline, the “fight-or-flight” hormone associated with increased energy (8).
However, at higher doses, these effects may become more pronounced, leading to anxiety and nervousness.
In fact, caffeine-induced anxiety disorder is one of four caffeine-related syndromes listed in the Diagnostic and Statistical Manual of Mental Disorders (DSM), which is published by the American Psychiatric Association.
Extremely high daily intakes of 1,000 mg or more per day have been reported to cause nervousness, jitteriness and similar symptoms in most people, whereas even a moderate intake may lead to similar effects in caffeine-sensitive individuals.
Additionally, modest doses have been shown to cause rapid breathing and increase stress levels when consumed in one sitting.
One study in 25 healthy men found that those who ingested approximately 300 mg of caffeine experienced more than double the stress of those who took a placebo.
Interestingly, stress levels were similar between regular and less frequent caffeine consumers, suggesting the compound may have the same effect on stress levels regardless of whether you drink it habitually
Nevertheless, these results are preliminary.
Coffee’s caffeine content is highly variable. For reference, a large (“grande”) coffee at Starbucks contains about 330 mg of caffeine.
If you notice that you often feel nervous or jittery, it might be a good idea to look at your caffeine intake and cut it back.
SUMMARY: Although low-to-moderate doses of caffeine can increase alertness, larger amounts may lead to anxiety or edginess. Monitor your own response in order to determine how much you can tolerate.
Caffeine’s ability to help people stay awake is one of its most prized qualities.
On the other hand, too much caffeine can make it difficult to get enough restorative sleep.
Studies have found that higher caffeine intake appears to increase the amount of time it takes to fall asleep. It may also decrease total sleeping time, especially in the elderly.
By contrast, low or moderate amounts of caffeine don’t seem to affect sleep very much in people considered “good sleepers,” or even those with self-reported insomnia.
You may not realize that too much caffeine is interfering with your sleep if you underestimate the amount of caffeine you’re taking in.
Although coffee and tea are the most concentrated sources of caffeine, it is also found in soda, cocoa, energy drinks and several types of medication.
For example, an energy shot may contain up to 350 mg of caffeine, while some energy drinks provide as much as a whopping 500 mg per can.
Importantly, the amount of caffeine you can consume without affecting your sleep will depend on your genetics and other factors.
In addition, caffeine consumed later in the day may interfere with sleep because its effects can take several hours to wear off.
Research has shown that while caffeine remains in your system for an average of five hours, the time period may range from one and a half hours to nine hours, depending on the individual. (4)
One study investigated how the timing of caffeine ingestion affects sleep. Researchers gave 12 healthy adults 400 mg of caffeine either six hours before bedtime, three hours before bedtime or immediately prior to bedtime.
Both the time it took all three groups to fall asleep and the time they spent awake at night increased significantly.
These results suggest that it’s important to pay attention to both the amount and timing of caffeine to optimize your sleep.
SUMMARY: Caffeine can help you stay awake during the day, but it may negatively impact your sleep quality and quantity. Cut off your caffeine consumption by the early afternoon to avoid sleeping problems.
3. Digestive Issues
Many people find that a morning cup of coffee helps get their bowels moving.
Coffee’s laxative effect has been attributed to the release of gastrin, a hormone the stomach produces that speeds up activity in the colon. What’s more, decaffeinated coffee has been shown to produce a similar response
However, caffeine itself also seems to stimulate bowel movements by increasing peristalsis, the contractions that move food through your digestive tract
Given this effect, it’s not surprising that large doses of caffeine may lead to loose stools or even diarrhea in some people.
Although for many years coffee was believed to cause stomach ulcers, a large study of more than 8,000 people didn’t find any link between the two
On the other hand, some studies suggest that caffeinated beverages may worsen gastroesophageal reflux disease (GERD) in some people. This seems to be especially true of coffee.
In a small study, when five healthy adults drank caffeinated water, they experienced a relaxation of the muscle that keeps stomach contents from moving up into the throat — the hallmark of GERD.
Since coffee can have major effects on digestive function, you may want to cut back on the amount you drink or switch to tea if you experience any issues.
SUMMARY:Although small to moderate amounts of coffee can improve gut motility, larger dosages may lead to loose stools or GERD. Reducing your coffee intake or switching to tea may be beneficial.
Despite all of caffeine’s health benefits, there’s no denying that it may become habit-forming.
A detailed review suggests that although caffeine triggers certain brain chemicals similar to the way cocaine and amphetamines do, it does not cause classic addiction the way these drugs do
However, it may lead to psychological or physical dependency, especially at high dosages.
In one study, 16 people who typically consumed high, moderate or no caffeine took part in a word test after going without caffeine overnight. Only high caffeine users showed a bias for caffeine-related words and had strong caffeine cravings.
Additionally, the frequency of caffeine intake seems to play a role in dependency.
In another study, 213 caffeine users completed questionnaires after going 16 hours without consuming it. Daily users had greater increases in headaches, fatigue and other withdrawal symptoms than non-daily users
Even though the compound does not seem to cause true addiction, if you regularly drink a lot of coffee or other caffeinated beverages, there’s a very good chance you may become dependent on its effects.
SUMMARY: Going without caffeine for several hours may lead to psychological or physical withdrawal symptoms in those who consume large amounts on a daily basis.
5. High Blood Pressure
Overall, caffeine doesn’t seem to increase the risk of heart disease or stroke in most people.
However, it has been shown to raise blood pressure in several studies due to its stimulatory effect on the nervous system
Elevated blood pressure is a risk factor for heart attack and stroke because it may damage arteries over time, restricting the flow of blood to your heart and brain.
Fortunately, caffeine’s effect on blood pressure seems to be temporary. Also, it seems to have the strongest impact on people who aren’t used to consuming it.
High caffeine intake has also been shown to raise blood pressure during exercise in healthy people, as well as in those with mildly elevated blood pressure.
Therefore, paying attention to the dosage and timing of caffeine is important, especially if you already have high blood pressure.
SUMMARY: Caffeine seems to raise blood pressure when consumed at high doses or prior to exercise, as well as in people who rarely consume it. But this effect may only be temporary, so it’s best to monitor your response.
6. Rapid Heart Rate
The stimulatory effects of high caffeine intake may cause your heart to beat faster.
It may also lead to altered heartbeat rhythm, called atrial fibrillation, which has been reported in young people who consumed energy drinks containing extremely high doses of caffeine.
In one case study, a woman who took a massive dose of caffeine powder and tablets in an attempted suicide developed a very rapid heart rate, kidney failure and other serious health issues.
However, this effect doesn’t seem to occur in everyone. Indeed, even some people with heart problems may be able to tolerate large amounts of caffeine without any adverse effects.
In one controlled study, when 51 heart failure patients consumed 100 mg of caffeine per hour for five hours, their heart rates and rhythms remained normal
Regardless of the mixed study results, if you notice any changes in your heart rate or rhythm after drinking caffeinated beverages, consider decreasing your intake.
SUMMARY: Large doses of caffeine may increase heart rate or rhythm in some people. These effects appear to vary greatly from person to person. If you feel them, consider reducing your intake.
Coffee, tea and other caffeinated beverages are known to boost energy levels.
However, they can also have the opposite effect by leading to rebound fatigue after the caffeine leaves your system.
One review of 41 studies found that although caffeinated energy drinks increased alertness and improved mood for several hours, participants were often more tired than usual the following day
Of course, if you continue to drink lots of caffeine throughout the day, you can avoid the rebound effect. On the other hand, this may affect your ability to sleep.
To maximize caffeine’s benefits on energy and avoid rebound fatigue, consume it in moderate rather than high doses.
SUMMARY:Although caffeine provides energy, it can indirectly lead to fatigue when its effects wear off. Aim for moderate caffeine intake to help minimize rebound fatigue.
8. Frequent Urination and Urgency
Increased urination is a common side effect of high caffeine intake due to the compound’s stimulatory effects on the bladder.
You may have noticed that you need to urinate frequently when you drink more coffee or tea than usual.
Most research looking at the compound’s effects on urinary frequency has focused on older people and those with overactive bladders or incontinence
In one study, 12 young to middle-aged people with overactive bladders who consumed 2 mg of caffeine per pound (4.5 mg per kilogram) of body weight daily experienced significant increases in urinary frequency and urgency
For someone weighing 150 pounds (68 kg), this would equate to about 300 mg of caffeine per day.
In addition, high intake may increase the likelihood of developing incontinence in people with healthy bladders.
One large study looked at the effects of high caffeine intake on incontinence in more than 65,000 women without incontinence.
Those who consumed more than 450 mg daily had a significantly increased risk of incontinence, compared to those who consumed less than 150 mg per day.
If you drink a lot of caffeinated beverages and feel that your urination is more frequent or urgent than it should be, it may be a good idea to cut back on your intake to see if your symptoms improve.
SUMMARY: High caffeine intake has been linked to increased urinary frequency and urgency in several studies. Reducing your intake may improve these symptoms.
The Bottom Line
Light-to-moderate caffeine intake seems to provide impressive health benefits in many people.
On the other hand, very high dosages may lead to side effects that interfere with day-to-day living and might even cause serious health issues.
Although responses vary from person to person, the effects of high intake demonstrate that more isn’t necessarily better.
To get the benefits of caffeine without undesirable effects, conduct an honest assessment of your sleep, energy levels and other factors that might be affected, and reduce your intake if needed.