Over 2.25 billion cups of coffee are consumed worldwide daily, according to 2024 statistics of Drive Research. About 66% of Americans make coffee at home daily. And, about 87% of Americans consider themselves partially or fully obsessed with coffee.
These stats are a testament to the popularity of coffee.
Aside from the irresistible aroma and bold flavor, coffee offers numerous health benefits thanks to its nutrient-rich profile. It contains caffeine, anti-oxidants, minerals, and other beneficial nutrients that promote mental alertness, support metabolism, and enhance physiological functions.
But, there’s another side to the coin as well.
Drinking coffee may cause certain unpleasant side effects, mainly due to its high caffeine content. A high daily dose of caffeine is linked to insomnia, restlessness, nervousness, rapid heartbeat, nausea, and several other side effects.
These side effects usually occur when daily consumption surpasses 400 mg of caffeine or 4-5 cups of coffee. Even 400 mg can cause side effects in people with increased caffeine sensitivity or those who metabolize caffeine slowly.
Extra sensitivity to caffeine can be attributed to certain health conditions. For instance, people with anxiety or panic disorder may find their symptoms worsening after drinking caffeinated coffee, according to a study named Genetics of Caffeine.
Similarly, some medications intensify caffeine’s effects. Those medicines include:
- Cimetidine
- Quinolone antibiotics, such as ciprofloxacin, moxifloxacin, and levofloxacin
- Birth control pills that contain estrogen
- Disulfiram
- Verapamil
- Antidepressants
All this implies that although coffee has a lot of health benefits, it also has certain risks. And since most of these risks are associated with excessive caffeine consumption, being mindful of your daily coffee intake is imperative.
What Happens When You Drink Too Much Coffee?
With every additional cup of coffee during the course of a day, you consume more caffeine. You have nothing to worry about if your total caffeine intake remains under 400 mg. However, if this threshold is exceeded, you may start experiencing unfavorable side effects, such as headaches, insomnia, and irritability, to name a few.
But why is that so?
Caffeine in coffee is a psychoactive agent that stimulates the nervous system. When consumed, it is absorbed by the small intestine. It reaches the bloodstream 30 to 60 minutes after consumption. This results in an energy boost and increased mental alertness.
However, drinking too much coffee may cause side effects as the body receives more caffeine than it can efficiently absorb. The risk of side effects is even higher if you have caffeine sensitivity or a slow caffeine absorption rate.
Here are the most common side effects of coffee and caffeine.
1. Insomnia
A cup of coffee in the morning helps ward off sleepiness and promotes mental alertness. This sounds great if you want to make the most out of your job and other commitments of the day. However, there is also a downside.
Regular caffeine consumption can delay your night slumber and may contribute to less hours of sleep. It may also reduce the amount of slow wave sleep, a deep sleep stage contributing significantly to the body’s recovery. A chronic reduction of deep wave sleep can lead to problems in crucial processes like:
- Cognitive functions
- Tissue repair and growth of both muscles and bones
- Clearing the brain and spinal cord of harmful proteins and other waste products
- Immune function
How Can Caffeine Affect Your Sleep? The caffeine in coffee works to block adenosine receptors, preventing their response to adenosine release.
Adenosine is a neurochemical created and released in the brain. After its release, it binds to adenosine receptors. This process works to suppress the central nervous system, causing drowsiness.
When you drink coffee, its caffeine content prevents adenosine from binding to adenosine receptors. Simultaneously, it stimulates nervous system activity, promoting alertness in both mind and body.
While a moderate amount of caffeine can help you stay alert in the day without causing sleep issues, overconsumption can cause problems. A daily caffeine intake can reduce adenosine activity in a chronic manner, lowering the quality of slow wave sleep, according to a study on the impact of daily caffeine intake.
How To Drink Coffee Without Affecting Sleep? To avoid sleep issues, refraining from coffee and caffeine consumption 6-8 hours before bedtime may help, according to a study on Caffeine Effects on Sleep. Ideally, you should drink your last cup of joe no later than 2 PM.
Moreover, it is important not to consume more than 400 mg of caffeine, which usually equates 4-5 cups of coffee.
Even 400 mg of caffeine can cause side effects if you have issues like anxiety, digestive issues, or impaired immune function. You should consult your doctor to determine a safe amount.
2. Anxiety
Caffeine consumption is linked to nervousness and increased heart rate. Overconsumption can lead to caffeine-induced anxiety, although a moderate amount of caffeine is known to support mental health.
The most common symptoms of caffeine-induced anxiety are:
- Headache
- Nervousness
- Restlessness
- Sweating
- Lack of sleep
How Does Caffeine Cause Anxiety? Caffeine works to stimulate the nervous system and triggers the release of adrenaline. While adrenaline release increases energy levels, too much of it can cause feelings of nervousness and anxiety. Caffeine also causes the release of cortisol, which is infamously known as stress hormone.
Another caffeine’s mechanism of action involves the blocking of adenosine receptors. As a result, they do not let adenosines bind with them. This process primarily helps you stay alert but may also cause anxiety-like symptoms.
That said, these mechanisms usually lead to anxiety symptoms only when caffeine is over consumed. According to research, extremely high dosages of caffeine (1000 mg - 1500 mg) can lead to certain neuropsychiatric effects like jitteriness and nervousness. Normal dosage (around 400 mg), although safe for most individuals, may also cause these side effects in caffeine-sensitive people.
3. Fast Heartbeat (Tachycardia)
Caffeine can affect the heartbeat. It’s usually only a slight effect when moderate amount of coffee or caffeine is consumed. It may not be even noticeable. However, overconsumption can lead to a markedly fast heartbeat, also called tachycardia.
Tachycardia refers to a heart rate above 100 beats per minute, according to the American Heart Association (AHA). For reference, normal heart rate ranges from 60 bpm to 100 bpm. Even so, it is important to consult a doctor if the resting heart rate stays over 90 bpm for a long time.
Why Does Caffeine Make Your Heart Rate Increase? Caffeine consumption triggers the release of norepinephrine, also called noradrenaline. It is a neurotransmitter and hormone that works to increase the heart rate by causing vasoconstriction.
While a fast heartbeat helps accelerate metabolic responses and may contribute to fat burning, it can be problematic for some people. More specifically, people with increased caffeine sensitivity or conditions like arrhythmia (irregular and fast heartbeat) may experience palpitations after ingesting caffeine. Normal individuals may also have a higher risk of arrhythmia if they regularly take higher doses, according to a study published by AHA.
4. Digestive Issues (Stomach Upset, Acid Reflux)
Coffee is known for its natural laxative effect. This effect occurs due to the release of a gastrin hormone, which increases bowel activity.
The laxative effect of coffee on the gastrointestinal tract is usually relieving. However, it is uncomfortable for some people. This happens particularly in the case of coffee overconsumption.
Consuming coffee in excessive amounts or when you have increased caffeine sensitivity may lead to the following problems:
- Dyspepsia (discomfort, nausea, poor digestion, heartburn, and flatulence)
- Esophageal burns
- Gastritis or ulcers
- Gastro-esophageal reflux disease (GERD)
It is logical to assume that caffeine is the reason for the issues mentioned above. But decaffeinated coffee has also been linked to a stimulated bowel movement, according to a study titled 'Effect of Coffee on Distal Colon Function.'.
This is because coffee contains several compounds other than caffeine that can contribute to issues like an upset stomach and acid reflux.
Let’s have an overview of coffee compounds that may contribute to digestive problems:
A. Caffeine
Extra caffeine consumption has been found to increase the production of stomach acid. This can cause certain problems, such as acid reflux, heartburn, and GERD.
C. Additives
In some cases, coffee alone is not the reason for digestive issues; introducing additives has also been found to cause upset stomach. Ingredients like milk, cream, and sugar may contribute to bloating, diarrhea, and stomach cramps, especially in people who have trouble digesting lactose.
5. Tremors
One of the risks associated with drinking coffee is muscle tremors, commonly referred to as 'coffee jitters.' Drinking too much coffee or other caffeinated beverages can cause shaky hands or jitteriness in the entire body.
The reason is that caffeine is a stimulant for the central nervous system. It can accelerate heartbeat and increase blood pressure, causing tremors or shakiness.
According to research, tremors can occur as a side effect of caffeine consumption. Caffeine has also been found to exacerbate the existing tremor ailment called Essential Tremors.
Sometimes, tremors occur when you stop drinking coffee or caffeinated drinks. It is a withdrawal symptom that usually lasts 9-12 days. It can occur in habitual coffee drinkers who abruptly stop drinking coffee after developing emotional and physiological caffeine dependence, according to an article published by the National Library of Medicine.
6. Headache
The link between caffeinated coffee and headache is somewhat complicated. For some people, drinking coffee can cause headaches, while some get headache relief. This is because everyone responds differently to caffeine consumption. The amount of daily dosage and the body’s sensitivity to caffeine are the top contributing factors.
Here are some of the reasons caffeine consumption may lead to headaches.
A. Drinking Too Much Caffeine
According to several studies, the maximum limit of caffeine intake for a normal person is 400 mg, which roughly equates to four to five cups of coffee. Exceeding this amount can cause headache, among several other side effects. People with caffeine sensitivity may experience side effects even with lesser amounts.
B. Medication Overuse
Some amount of caffeine can help relieve certain headaches. This makes caffeine a somewhat pain reliever. However, a daily intake can contribute to what’s commonly known as medication overuse headache, also called rebound headache.
C. Dehydration
Caffeine, due to its diuretic effect, may increase urination. This can lead to dehydration, which can trigger a headache. Increased urination may also lower magnesium levels in the body, which can also cause headaches.
D. Sleep deprivation
Caffeine is a psychoactive ingredient that stimulates the central nervous system and promotes alertness. The side effect of this is reduced sleep time, which can cause migraine headaches. However, with certain precautions, such as limiting the consumption to 400mg max and avoiding it after 2 PM, you can prevent caffeine from interfering with your sleep.
7. Caffeine Dependency And Withdrawal
Caffeine uses its stimulatory effect to boost mood, concentration, and energy in the body. It does so by increasing dopamine levels. This pattern somewhat resembles the effects of substance abuse, but it is not large enough to unbalance the brain’s reward system. For this reason, the American Psychiatric Association does not recognize caffeine addiction or dependency as a substance use disorder.
However, quitting the chronic use of caffeine is linked to withdrawal symptoms, such as fatigue, loss of concentration, drowsiness, anxiety, irritability, and many others.
Fortunately, caffeine withdrawal symptoms do not last very long. Also, there are ways you can reduce or even avoid these symptoms while cutting back on your caffeine intake, such as the following:
- Reduce the caffeine consumption gradually and consistently. This will help prevent the associated withdrawal symptoms.
- If you have been drinking caffeinated coffee, switch to the decaf version. However, this shift should be in steps: start taking half-decaf, then move to full-decaffeinated coffee after some days. This will help reduce caffeine dependence without causing withdrawal issues.
- Get enough sleep: Caffeine withdrawal can cause fatigue, and the best way to combat it is to get enough sleep. Your body’s natural recovery will take care of the rest.
- Stay hydrated: Fatigue and headache are among the worst symptoms of caffeine withdrawal. Drinking plenty of water can prevent or reduce these symptoms.
- Use other sources of energy: Quitting caffeine can cause energy levels to drop. You can replenish these levels by adopting a healthy diet and exercise regimen. Make sure to hit the ground daily and add nutrient-rich foods to your daily diet.
8. Increased Blood Pressure
Caffeine can cause a short-term spike in blood pressure, even if your blood pressure stays normal. Generally, this spike occurs in people who do not regularly drink coffee or caffeinated beverages. The degree of blood pressure rise may vary from person to person.
A meta-analysis of randomized controlled trials suggests an average increase of 3.04 mmHg for systolic blood pressure SBP and 2.45 mmHg for diastolic blood pressure DBP in response to short-term (less than one week) caffeine consumption. The spike appeared to be more pronounced in adolescents compared to adult participants.
That said, regular coffee consumption has not been found to increase blood pressure. This is because regularly drinking coffee builds tolerance against caffeine. Various studies also deny the link between caffeine consumption and a higher risk of hypertension.
According to the FDA, coffee consumption that supplies 400 mg of caffeine tends to be safe if you do not have high blood pressure. Individual tolerance may, however, vary depending on how well your body metabolizes caffeine after consumption.
Instructions for people with hypertension are usually different. Doctors usually advise them not to drink caffeinated coffee in excessive amounts as it may cause a “pressor response.”
9. Frequent Urination
Caffeine in coffee can make you pee more. This is because caffeine can increase blood pressure and get your kidneys to work out of schedule. The added pressure affects the kidney’s ability to reabsorb water and salt, causing more urine to pass into the bladder.
A caffeine dosage of more than 4.5 mg/kg may cause diuresis and incontinence, according to a study on the Effect of caffeine on bladder function. In simple words, drinking more than four cups of coffee may cause symptoms of an overactive bladder, even if you haven’t experienced any symptoms before.
Moreover, drinking caffeinated coffee may worsen overactive bladder symptoms. People who chronically urinate more than others may feel a heightened urge to pee after consuming as little as 200mg of caffeine.
How Much Caffeine Is Too Much in One Day?
An average person can safely consume up to 400 mg of caffeine or 4-5 cups of coffee. This amount doesn’t usually lead to health risks in healthy individuals. However, the risks of side effects occur once this limit is surpassed.
Even 400 mg of caffeine may be too much for individuals with caffeine sensitivity.
Caffeine sensitivity can develop due to the following reasons:
- Slower metabolism: The caffeine metabolism rate significantly depends on a specific gene called CYP1A2. This gene has two variants: the fast metabolizing and the slow metabolizing. People with a slow metabolizing CYP1A2 do not absorb caffeine quickly and are more likely to experience caffeine-induced side effects even after moderate consumption.
- Adenosine Receptor Sensitivity: Caffeine blocks adenosine receptors in the brain to reduce drowsiness and promote alertness. Some people have extra sensitive adenosine receptors and are more likely to have a more pronounced caffeine effect. Increased adenosine receptors’ sensitivity may be attributed to a specific variation of the ADORA2A gene, according to a 2012 study on Individual Caffeine Sensitivity published by NCBI.
- Certain medications: Some drugs and supplements can make the caffeine effect more pronounced. These include medicines like theophylline and herbal supplements like echinacea and ephedrine.
People with caffeine sensitivity should consult their doctors to determine a safe amount of intake.