The Hidden Risks of Coffee Consumption

Coffee

Coffee is a beverage prepared from roasted coffee beans, which are the seeds of the coffee plant scientifically known as Coffea arabica. It is commonly consumed as a stimulant, with millions of people drinking it daily to enhance alertness and concentration and reduce fatigue. Coffee is also used in the prevention and treatment of various health conditions. The coffee plant can grow up to 8 meters tall, has glossy dark green leaves measuring 6 to 20 cm in length and 2.5 to 6 cm in width. While there has been much debate over the origin and native region of coffee, it is currently cultivated in many tropical regions such as Brazil, Mexico, Colombia, and Ethiopia. Coffee ranks among the most popular beverages worldwide, primarily consumed for its caffeine content, as well as its distinctive flavor and aroma that attract many people.

Coffee consumption is associated with several health benefits, including improved alertness and mental clarity, reduced risk of colon and rectal cancer, prevention of dizziness in older adults, and protection against Parkinson’s disease, gallstones, type 2 diabetes, liver diseases (such as cirrhosis and hepatocellular carcinoma). However, excessive coffee intake may lead to various adverse effects, often linked to high caffeine consumption and unhealthy behaviors such as smoking and physical inactivity, which frequently accompany coffee drinking. This article details the main harms associated with coffee consumption and examines scientific perspectives on the matter.

Side Effects of Coffee

Consuming up to 400 mg of caffeine per day—equivalent to about four cups of coffee—is generally considered safe and not harmful to health, though other sources of caffeine should be taken into account. Despite the numerous benefits and overall safety of moderate coffee consumption, excessive intake can lead to several negative effects. These include:

• Elevated risk of heart and artery diseases: Several case-control studies have found that heavy coffee consumption is linked to a higher risk of coronary artery disease and myocardial infarction. Individuals who drink five or more cups of coffee daily face a 40–60% greater risk compared to non-consumers. Those consuming at least 600 ml of coffee per day have a threefold higher risk of acute coronary syndrome than non-drinkers. Conversely, individuals consuming less than 300 ml per day showed lower risk than abstainers. However, large prospective cohort studies have generally found no significant association between coffee consumption and cardiovascular diseases. A Norwegian study noted an increased risk only among those consuming nine or more cups daily after 12 years of follow-up. Additionally, coffee may trigger heart attacks in individuals with existing cardiac risk factors who do not regularly consume coffee, with risk increasing within an hour of consumption.
• Impact on individuals with coronary artery disease: Scientific evidence on coffee's effect on those already suffering from coronary artery disease is limited. However, consuming ten or more cups daily may raise the risk of sudden cardiac arrest. A study involving 1,935 individuals with prior myocardial infarction found no link between coffee consumption and mortality risk over four years. In both studies, only a small number of participants consumed such high quantities. Daily intake of five or more cups is generally considered unsafe for heart patients.
• Increased risk of stroke: A study on men with hypertension—a high-risk group—found that those consuming at least 700 ml of coffee daily had double the stroke risk compared to non-drinkers. Other studies have shown no such link. Overall, research on coffee and stroke remains limited, and further investigation is needed, especially in high-risk populations.
• Boiled (unfiltered) coffee increases total blood cholesterol, LDL (bad cholesterol), and triglycerides. These effects are reduced when coffee is filtered.
• High coffee consumption has been shown to elevate homocysteine levels in the blood, which is directly associated with heart and artery diseases. Abstaining from coffee for six weeks in individuals who typically drink four cups daily results in an 11% reduction in homocysteine. Folic acid supplementation can prevent this increase. The compounds cafestol and kahweol, present in unfiltered coffee, are responsible for this effect.
• Scientific studies confirm that coffee causes an immediate and temporary rise in blood pressure in both normotensive individuals and those with hypertension. Consuming 200–250 mg of caffeine (equivalent to 2–3 cups) increases systolic blood pressure by 3–14 mmHg and diastolic pressure by 4–13 mmHg in healthy individuals. This effect may be more pronounced in hypertensive patients. Although regular coffee consumption leads to partial tolerance, the pressor effect persists even in habitual drinkers. Long-term studies on coffee’s impact on hypertension risk yield inconsistent results—some show a positive correlation, others an inverse relationship, and some none at all. Overall, the long-term association appears weak and requires further research.
• Early case-control studies suggested a possible link between coffee and pancreatic, bladder, and ovarian cancers. However, better-designed recent studies have found no association between coffee or caffeine consumption and these cancers, nor with stomach, breast, or prostate cancers.
• Coffee reduces calcium absorption and increases its excretion in urine. High coffee intake has been linked to lower bone mineral density and a higher risk of osteoporosis and fractures, although some studies found no such link when adequate calcium intake was maintained.
• Polyphenolic compounds in coffee bind to iron and inhibit its absorption. Drinking 150–250 ml of coffee with meals can reduce non-heme iron absorption by 24–73%. Discontinuing coffee improves iron absorption from supplements. Therefore, coffee should be avoided with meals to enhance iron uptake.
• Coffee contains substances that bind to zinc and reduce its absorption. Although human studies are limited, in-vitro research shows coffee reduces zinc bioavailability by 21–32%. One report confirms reduced zinc absorption with coffee consumption, while another found no improvement in blood zinc levels after stopping coffee.
• Some studies indicate that high caffeine or coffee intake (400–800 mg daily) may delay fertilization. Two studies found reduced pregnancy likelihood in women consuming at least 300 mg of caffeine daily. However, many of these studies did not control for confounding factors like smoking or alcohol use. Other studies found no link between coffee and fertility. Based on current evidence, women experiencing fertility issues should avoid exceeding 300 mg of caffeine per day.
• Some studies have linked heavy coffee consumption to miscarriage.
• Multiple studies show that consuming 200–400 mg of caffeine daily during pregnancy is associated with a reduction in birth weight by approximately 100 grams. Intake exceeding 150 mg per day increases the risk of low birth weight by 50%. Many studies also link caffeine consumption to delayed fetal growth.
• High coffee intake by breastfeeding mothers can cause infant irritability, sleep disturbances, and gastrointestinal discomfort.
• Children should not consume more than 2.5 mg of caffeine per kg of body weight per day. Intakes above 3 mg/kg are associated with irritability, sleep disruption, and anxiety. There is insufficient data on the effects of high coffee consumption in children.
• Older adults experience higher blood caffeine levels than usual, increasing the risk of drug interactions. Coffee may also exacerbate the already elevated risk of osteoporosis and fractures in this group, particularly in the presence of calcium and vitamin D deficiency. Some studies suggest coffee may have more pronounced negative effects in elderly individuals.

Side Effects

Coffee is generally safe for most adults. However, excessive consumption may cause side effects such as irregular heartbeat, palpitations, insomnia, anxiety, restlessness, tremors, headaches, tinnitus, abdominal pain, nausea, vomiting, diarrhea, frequent urination, and increased breathing rate. Drinking six cups of coffee daily may lead to what is known as coffee dependence, characterized by anxiety and irritability.

Caffeine withdrawal symptoms may occur in individuals who have consumed coffee regularly over a long period, even at low daily amounts. Symptoms have been observed in those drinking as little as 100 ml daily, becoming more pronounced with higher habitual intake. These symptoms include headache, fatigue, dizziness, irritability, difficulty concentrating, and mood disturbances. Withdrawal may also cause nausea and muscle pain (myalgia). Symptoms are milder when caffeine is tapered gradually rather than stopped abruptly.

Contraindications

Caution is advised when consuming coffee in the following cases:

• Pregnancy and breastfeeding: Up to two cups of coffee per day (containing up to 200 mg of caffeine) is generally considered safe during pregnancy. Higher intake increases the risk of miscarriage, premature birth, and low birth weight, with risks rising proportionally to consumption. For nursing mothers, one to two cups daily is safe, but higher amounts may cause digestive irritation, irritability, and sleep problems in the infant.
• Children: Caffeinated coffee is not considered safe for children, as side effects tend to be more severe in this age group.
• Anxiety disorders: Coffee may worsen symptoms in individuals with anxiety conditions.
• Bleeding disorders: Coffee may exacerbate bleeding tendencies.
• Heart diseases: As mentioned earlier, unfiltered coffee raises blood lipids and homocysteine levels, increasing the risk of cardiovascular disease.
• Diarrhea: High caffeine intake may worsen diarrhea.
• Irritable bowel syndrome: Large amounts of caffeine may aggravate IBS symptoms and diarrhea.
• Glaucoma: Caffeine-containing coffee increases intraocular pressure within 30 minutes of consumption, lasting at least 90 minutes.
• High blood pressure: Coffee may raise blood pressure in hypertensive individuals, though regular consumers may develop partial tolerance.
• Osteoporosis: Caffeine increases urinary calcium excretion. Individuals with osteoporosis should limit caffeine to no more than 300 mg daily (about 2–3 cups). Calcium loss can be offset with dietary supplements. Extra caution is needed for postmenopausal women with genetic impairments in vitamin D metabolism.

Drug Interactions

Caffeine interacts with many medications. Key interactions include:

• Coffee interacts with ephedrine, both being stimulants, thereby increasing the risk of side effects.
• Caffeine may reduce the effectiveness of certain drugs, including adenosine (used in cardiac stress tests), alendronate, dipyridamole, lithium (abruptly stopping coffee may increase lithium side effects), pentobarbital, phenothiazines (coffee should be avoided one hour before and two hours after intake), and some tricyclic antidepressants like amitriptyline and imipramine (coffee reduces their absorption). Coffee has a lesser effect on diabetes medications, as caffeine may raise blood sugar levels, reducing drug efficacy.
• Some medications slow caffeine metabolism, increasing its blood levels and side effects. These include alcohol, certain antibiotics (ciprofloxacin, enoxacin, norfloxacin, sparfloxacin, grepafloxacin), disulfiram, estrogen, fluvoxamine, verapamil, levothyroxine, oral contraceptives, cimetidine, fluconazole, mexiletine, and terbinafine.
• Coffee may impair the elimination of certain drugs, raising their blood levels and side effect risks. Examples include clozapine and riluzole.
• Coffee may enhance the effects of certain medications, including MAO inhibitors (phenelzine, tranycypromine), anticoagulants (aspirin, clopidogrel, diclofenac, ibuprofen, naproxen, dalteparin, enoxaparin, heparin, warfarin), phenylpropanolamine, riluzole, stimulant drugs (diethylpropion, epinephrine, phentermine, pseudoephedrine), and theophylline.

References

1. ^ ^{A B T TH J H Kh D Dh R Z S Sh} "Find a Vitamin or Supplement: COFFEE", webmd. Edited.
2. ^ ^{A B} "Caffeine: How much is too much?", mayo clinic. Edited.
3. ↑ Fleming T, PDR for Herbal Medicines, Page 202-205. Edited.
4. ^ ^{A B T TH J H Kh D Dh R Z S Sh S D T Z F Q} Higdon J. V. and Freiz B. , "Coffee and Health: A Review of Recent Human Research", Critical Reviews in Food Science and Nutrition, Issue 46, Folder 2, Page 101-123. Edited.