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Side Effects of Too Much Caffeine and Coffee

Coffee is a beverage produced from roasted coffee beans from the Coffea plant. Coffee is widely consumed for its good taste, alleviation of exhaustion, and promoting mental alertness. It has also been shown to prevent or alleviate Parkinson’s disease, dementia, certain cancers, and various other diseases.

But there is the other side, too. Coffee contains caffeine, which can have adverse side effects. These include sleeplessness, agitation and restlessness, gastrointestinal distress, increased heart and breathing rate, headaches, anxiety, agitation, ringing in the ears, and chest pain. Coffee is most dangerous when consumed for an extended period or in amounts above 4 cups per day, which equates to about 400 mg of caffeine.

possible harms of coffee

While many people are concerned that their caffeine use may put them at risk, the average individual who consumes a cup or two of coffee has nothing to worry about.

1. Anxiety and Stress

Anxiety and Stress

Anxiety and stress are unpleasant states of emotion, usually due to anticipated events or adverse circumstances. Anxiety is described as an undesirable state of inner agitation, including negative feelings like fear and worry. Prolonged anxiety can be diagnosed as an anxiety disorder. Stress is characterized as a state of mental or emotional tension generated by negative occurrences, leading to anxiety. 

According to Harvard Medical School, caffeine use can imitate anxiety symptoms. In an article titled “Eating well to help manage anxiety: Your questions answered,” author Uma Naidoo, MD, explains that excessive caffeine consumption can result in symptoms like psychiatric conditions, including both stress and anxiety.

Related: What is caffeine?

2. Insomnia and Lack of Sleep


Insomnia and lack of sleep have been associated with caffeine consumption in prior studies – no surprise, given that caffeine is commonly used to promote energy and alertness. In a 2014 study titled “Exercise and Sport Performance with Low Doses of Caffeine,” researcher Lawrence L. Spriet found that a low dose of caffeine indeed supports improved performance for healthy individuals.

However, one of caffeine’s most common side effects is insomnia or lack of sleep. Insomnia is a sleeping disorder characterized by difficulty falling asleep or staying asleep, and evening caffeine intake is especially conducive to insomnia.

Another consequence of heavy caffeine consumption is a polysomnographic sleeping disorder, which consists of increased sleep latency, decreased stages 2 and 4 of non-rapid eye movement sleep, sleep fragmentation with quick arousals from sleep, and reduced sleeping duration.

A study by Christopher L. Drake, “Stress-related sleep disturbance and polysomnographic response to caffeine,” found that healthy individuals may display polysomnographic sleeping after caffeine consumption. Side effects include reduced total sleep time, trouble falling asleep, frequent evening and midnight awakenings, and daytime sleepiness. 

3. Digestive Issues and Dietary Problems

Digestive issues

Digestive issues and dietary problems are common for people who consume copious caffeine daily. This is because beverages with caffeine cause diuresis, in which more water is excreted from the body. Diuresis caused by caffeine can result in dehydration and constipation that can put your health at risk. Contrarily, caffeine can also cause diarrhea, usually only if a consumer has a bowel condition or irritable bowel syndrome. 

Caffeinated drinks can also provoke heartburn. In fact, in a 2006 review paper titled “Coffee and gastrointestinal function: facts and fiction. A review,” lead author P.J. Boekema found that heartburn was the most commonly reported gastrointestinal complaint related to caffeine. This arises because not only is coffee acidic in itself, but caffeine causes the stomach to discharge more acid. The feeling of heartburn comes when the stomach releases excessive acid, which flows back up to the esophagus.

For anyone with Gastroesophageal Reflux Disease, a common cause of heartburn, caffeine intake can worsen the symptoms. 

4. Muscle Breakdown and Catabolism

Muscle catabolism is the procedure where muscle tissues are broken down. It is a possible negative consequence of over-consumption of caffeine. Caffeine boosts cortisol production in the body, thereby increasing muscle catabolism (muscle wasting).

While caffeine contributes to several performance-enhancing effects for athletes – a stimulant that boosts alertness, endurance, and strength – it has no meaningful effect on muscle growth. Instead, a massive consumption in a short period can lead to rhabdomyolysis, in which damaged muscle fibers enter the bloodstream, as reported in the article “Rhabdomyolysis from Resistance Exercise and Caffeine Intake” by Dong Jun Sun et al. This can cause kidney failure among other serious problems.

5. Addiction and Over Consumption


Addiction and overconsumption of caffeine is diagnosed by checking daily caffeine dosage and gauging caffeine dependency. For example, athletes or workers might use energy drinks several times a day just to stay active or someone might consume caffeine to the point of anxiety. Caffeine intoxication and dependency are seldom diagnosed, though studies like “Caffeine Intoxication and Addiction” by Holly Pohler are helping to change that.

Symptoms of caffeine intoxication include turmoil, anxiety, hand tremors, stomach upset and fast or irregular heartbeats. Caffeine addicts may also suffer from sleeping disorders, frequent urination, and withdrawal headaches. Excessively high doses of caffeine can cause extreme agitation, convulsions, respiratory failure, and cardiac troubles. 

To avoid dependency and intoxication, it is recommended that daily caffeine consumption be less than 400 mg for adults. Young children should not consume caffeine at all. This includes all sources of caffeine, like energy drinks and chocolate, not just coffee. 

Related: Reasons Why Mormons Cannot Have Coffee

6. Unbalanced Blood Pressure

Unbalanced or elevated blood pressure is another possible effect of too much caffeine intake from coffee, cola, and energy drinks. The review study “Coffee, caffeine and blood pressure: a critical review” led by M-L Nurmien found that acute intake of coffee and caffeine does indeed increase blood pressure. People who drink caffeinated beverages daily usually have a higher average blood pressure average than those who don’t. So those with underlying high blood pressure are often advised to avoid caffeine.

7. High Heartbeat Rate

According to the review study “Impact of Caffeine on Heart Rate Variability: A Systematic Review” led by Julian Koenig, there is evidence to suggest that caffeine can increase your heart rate. However, the results were variable and not entirely conclusive.

Caffeine is one of the most popular and readily available stimulants, and stimulants are substances that stimulate the central nervous system and increase heart rate, which can cause palpitations and elevated blood pressure. As a result, when abused, caffeine can induce severe heart and blood vessel troubles such as high blood pressure, heart rhythm disturbances, and heart rate increase.

8. Lack of Energy and Fatigue


Lack of energy and fatigue results from the crash following a caffeine high. This crash can be worse in those with severe caffeine dependency as the body struggles to regulate highs and lows without the influence of the drug, eventually becoming unable to rest. When the body cannot rest and the adrenal glands are over-stimulated, the body crashes to compel rest—the human body’s method of returning to a vegetative state without further energy expense.

9. Urgency Feeling and Excessive Urination

Urgency feeling and excessive urination are results of excessive consumption of caffeinated coffee, cola, or energy drinks. Caffeine is a diuretic stimulant, resulting in frequent urination and intense urges to urinate. 

This condition can seriously interfere with your daily activities by exciting, frequent washroom trips, and in more severe contexts, it can cause urinary incontinence or affect the kidneys. This is especially true in those with an overactive bladder, according to the study “Effect of caffeine on bladder function in patients with overactive bladder symptoms” led by Supatra Lohsiriwat.

10. Dizziness

Dizziness is a minor effect that caffeine-dependent individuals sometimes experience. It can also be associated with headache and nausea symptoms.

11. Dehydration

Dehydration is a common side effect experienced by heavy coffee drinkers because caffeine has a diuretic effect that increases urination. This can lead to a risk of constipation, diarrhea, or a weakened immune system in severe cases. However, the article “The impact of caffeine on mood, cognitive function, performance, and hydration, review of benefits and risks” by C.H.S. Ruxton showed that it takes significant coffee intake (more than 4 cups a day) before one experiences negative consequences.

12. Muscle Tremors

Muscle tremors are an adverse side effect of excessive caffeine consumption, particularly in those with pre-existing conditions of which tremors are a symptom. Because caffeine is a stimulant, drinking caffeinated beverages like coffee, energy drinks, and colas can stimulate muscle activity, making tremors more intense or more frequent.

That said, for most people, tremors are a minor side effect of caffeine consumption. In the research paper “Caffeine and tremor” by William Koller, Sandra Cone, and Gregory Herbster, just 2% of subjects found that coffee consumption resulted in tremors. This increased to 6% when considering Parkinson’s patients.

13. Bone Loss

Daily consumption of high-dose caffeinated beverages can lead to bone loss. The acids present in coffee are directly connected with calcium loss, as the molecules bind with bone calcium and cause the minerals to be drained from the human body. Caffeine has been connected with a lower bone density as the human body ages, particularly in post-menopausal women. In the study “Is caffeine a risk factor for bone loss in the elderly?” author Linda K. Massey found that while younger people can compensate for caffeine’s effects by consuming more calcium, this doesn’t work as you age.

Not only does caffeine decrease the body’s ability to absorb calcium, but because it is a diuretic, it can also cause calcium to be rapidly excreted in the urine before the intestines fully absorb it.

Research – such as “Effects of caffeine on bone and the calcium economy” by R.P. Heaney – shows that caffeine can interfere with calcium absorption and contribute to bone thinning. To avoid this, healthy adults should not consume more than 400 mg of caffeine daily, adolescents shouldn’t consume more than 100 mg per day, and children shouldn’t consume caffeine at all.

14. Increased Cholesterol

Increased cholesterol is an adverse effect of drinking too much coffee. Cafestol and kahweol are two components of coffee beans that have been shown to increase LDL cholesterol levels. Filtering coffee through a paper filter, as when using a drip machine or brewing a pour-over, removes these components, but they are present in French press coffee and espresso.

For people with normal cholesterol levels, a cup of espresso contributes only negligibly to an increase in LDL. However, unfiltered coffee can put those with prior high cholesterol at risk, according to the study “Coffee, caffeine, and coronary heart disease” by Marilyn C. Cornelis and Ahmed El-Sohemy.

What are the possible side effects of coffee for different body functions?

The possible side effects of coffee on different body functions are below. Coffee has both negative and positive consequences for many parts of the body.

1. Coffee Side Effects for Bones

Bone thinning and bone loss are potential consequences of heavy caffeine consumption when it comes to the skeleton. The study above, “Is caffeine a risk factor for bone loss in the elderly?” stated that consuming an excessive amount may impair calcium absorption and metabolism, resulting in bone weakening. This is especially true for the elderly, in particular, post-menopausal women.

2. Coffee Side Effects for Diabetics

Drinking coffee can reduce your risk for diabetes, though excessive use of sweeteners or cream can increase your risk of diabetes and become overweight. Like everything else, moderation is the key to coffee consumption. 

A 2014 study, “Changes in coffee intake and subsequent risk of type 2 diabetes: three large cohorts of U.S. men and women,” led by Frank B. Hu found an 11% reduction in the risk of acquiring type 2 diabetes when coffee consumption was increased by more than one cup per day.

A more recent study, “Long-term effects of coffee and caffeine intake on the risk of prediabetes and type 2 diabetes: Findings from a population with low coffee consumption,” by P. Mirmiran et al. showed something else. Namely, long-term coffee and caffeine consumption may be associated with a decreased incidence of prediabetes and diabetes.

The study by James D. Lane, “Caffeine impairs glucose metabolism in type 2 diabetes,” demonstrated that consuming a caffeine capsule before a meal increased post-meal blood glucose levels in people who already have type 2 diabetes. Additionally, it demonstrated an increase in insulin resistance.

3. Coffee Side Effects for Hair

There are many claims about coffee’s effect on hair, though few are scientifically proven. It is said that coffee applied directly to the hair and scalp can restore hair growth, nurture softer and shinier hair, and eliminate gray hairs. According to some research, the caffeine in coffee can help stimulate hair growth and stop hair loss. This is based on the R. Paus study, “Differential effects of caffeine on hair shaft elongation, matrix, and outer root sheath keratinocyte proliferation, and transforming growth factor-β2/insulin-like growth factor-1-mediated regulation the hair cycle in male and female human hair follicles in vitro”. 

Since caffeine is a stimulant, it also boosts blood circulation to hair follicles, which can help hair grow faster and become stronger, giving the appearance of fuller and thicker hair. Rinsing hair with coffee can also improve dullness since it has flavonoids, antioxidants that stimulate hair regeneration.

4. Coffee Side Effects for PCOS

Polycystic ovary syndrome (PCOS) is a hormonal disorder typical for women of reproductive age. PCOS makes it more challenging to get pregnant, so women with this condition are typically told to limit caffeine intake not to impact fertility. Moderate caffeine consumption, 200 mg or less, is generally considered safe.

According to “Caffeine intake and delayed conception: a European multicenter study on infertility and subfecundity. European Study Group on Infertility Subfecundity,” women who used more than 500 mg of caffeine per day had a significantly increased odds ratio of subfecundity during their first pregnancy. Essentially, the study concluded that excessive caffeine use could result in a delay in conception. Alternatively, another research has shown that coffee may increase SHBG (Sex Hormone Binding Globulin) levels, alleviating PCOS symptoms by balancing hormones. This study was conducted in Japan by Chisato Nagata:  “Association of coffee, green tea, and caffeine intakes with serum concentrations of estradiol and sex hormone‐binding globulin in premenopausal Japanese women.”

PCOS patients tend to have hyper-responsive adrenal glands that secrete two essential hormones: epinephrine and cortisol. A danger for PCOS patients is that caffeine also boosts cortisol and epinephrine, mimicking an acute stress response. This is one reason caffeine consumption should be limited.

5. Coffee Side Effects for Liver

Research has shown that coffee helps increase antioxidant capacity by increasing glutathione levels and modulating various inflammatory mediators’ gene and protein expression. So moderate daily consumption of unsweetened coffee is an acceptable adjunct for liver therapy, especially for patients with chronic liver diseases. However, heavy consumption has been shown to reduce the activity of liver enzymes.

Coffee contributes to improvement in hepatic steatosis and fibrosis, decreasing cirrhosis and reducing the risk of hepatocellular carcinoma. Experimental studies were summarized in the review article “Coffee and liver health” by Filomena Morisco, Vincenzo Lembo, Giovanna Mazzone, Silvia Camera, Nicola Caporaso. They showed that coffee consumption lowers fat accumulation and collagen deposits in the liver. It also stimulates antioxidant capacity through additional glutathione and modulation of the gene and protein expression of various inflammatory mediators. 

Animal and in vitro research demonstrate that cafestol and kahweol, two diterpenes found in coffee, can help prevent liver cancer. They modulate the enzymes that serve to detoxify certain liver carcinogens. The extent of the benefits is unclear, but moderate coffee consumption is recommended to patients with chronic liver disease.

Can Coffee Harm the Unborn Baby?

The impact of coffee on an unborn fetus has long been a point of discussion. In general, high doses of caffeine are best avoided by pregnant women, but moderate consumption of less than 200 mg per day (from all caffeine sources, not just coffee) is considered safe.

Caffeine has been associated with several prenatal risks. When consumed in high doses, caffeine has been linked with increased rates of miscarriage, according to a study titled “Lifestyle and pregnancy loss in a contemporary cohort of women recruited before conception: The LIFE Study”, which followed 344 couples. The team, led by Germaine M. Buck Louis, reports in the journal Fertility and Sterility that consuming three or more caffeinated beverages per day increased the risk of miscarriage by 74%. 

Dr. Zev Williams of Albert Einstein College of Medicine and spokesman for the American College of Obstetricians and Gynecologists notes that a small amount of caffeine is acceptable. However, caffeine passes through the placenta in high doses and is absorbed by the unborn baby. While adult bodies can break down caffeine reasonably well, a developing baby can’t do this as efficiently. So the caffeine stored in their blood can reach dangerously high levels. 

Caffeine also affects other aspects of an unborn baby’s health, and it is known to increase the baby’s heart rate and affect how much they move in utero. Since caffeine is a diuretic, it may cause a fetus to receive less nutrition. Caffeine consumption may cause the mother to absorb less iron and calcium from foods, possibly harming fetal development. At high doses, caffeine may result in smaller-sized babies due to less calcium absorption from foods. 

The UK National Health System recommends that pregnant women in the UK limit caffeine consumption to less than 200 mg per day. The recommendation is based on a 2008 study in which pregnant women who consumed more than 200 mg caffeine a day were at a 25 percent higher risk of miscarriage in the first twenty weeks of their pregnancy. 

Does coffee have more side effects than tea?

Coffee has more side effects than tea because it contains more caffeine. Usually, 8 ounces of black tea contains only 25 – 48 mg of caffeine – and even lower in green tea, with only 25 – 29 mg. On the other hand, an 8-ounce cup of brewed black coffee contains 95 and 165 mg of caffeine. 

Even though tea and coffee both have caffeine as their stimulant, they have different effects on the human body. The body absorbs the caffeine in coffee much faster, which results in faster high energy levels. On the other hand, tea has the amino acid called L-theanine, which slows down the absorption of caffeine. As a result, you obtain a more neutral energy flow over a longer timeframe. This amino acid also helps reduce anxiety, makes you feel more relaxed, and not trigger drowsiness or dizziness. Both coffee and tea contain the benefits of antioxidants. 

Another side effect of caffeine in coffee is lower bone density. Research has shown that women who drink coffee suffer more from osteoporosis in the long run versus women who drink tea. This is likely due to coffee’s higher caffeine content, as caffeine prevents calcium absorption and promotes its excretion.

When it comes to weight loss, coffee drinkers tend to experience only short-term benefits and quickly develop a tolerance. On the other hand, tea seems to have a more positive effect, with studies showing tea drinkers have reduced body fat. 

Both coffee and tea offer various health benefits, but tea appears to be more beneficial with fewer adverse side effects due to its lower caffeine content. You can enjoy more cups of tea before facing the harmful effects of overconsumption of caffeine. For strong bones and weight loss, tea is recommended over coffee.

Julia Bobak
I love trail running, rock climbing, coffee, food, and my tiny dog — and writing about all of them. I start every morning with a fresh Americano from my home espresso machine, or I don’t start it at all.

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