caffee and cafaine
Most data regarding the health benefits and risks of caffeine come from observational studies in which self-reported consumption of caffeinated foods and beverages is correlated with health outcomes. Such studies make it difficult to determine whether caffeine itself is the causal factor and to rule out other explanations. Based on the available data, there is insufficient evidence to either encourage or discourage the regular consumption of coffee and/or tea.
Caffeine has multiple systemic effects on the nervous, psychological, cardiovascular, endocrine, and gastrointestinal systems.
Safe Levels
For most adults, consumption of up to 400 mg of caffeine per day appears to be safe — equivalent to less than five cups of coffee daily.
Limited data exist on safe levels of caffeine intake for children and adolescents. A systematic review found that a daily intake of 2.5 mg of caffeine per kilogram of body weight was not associated with adverse effects. Young people should be warned against excessive consumption of caffeine-containing energy drinks and against mixing them with other substances.
Coffee
More than 150 million people in the United States drink coffee daily, making it an important environmental exposure. Coffee is preferred over tea in developed countries—especially in Europe (except England and Ireland), Australia, and the Americas. The developed world accounts for 71.5% of global coffee consumption.
The average coffee consumption among adults in the United States is about two cups per day, equivalent to approximately 280 mg of caffeine, though the caffeine content varies widely.
Some researchers classify individuals who consume four or more cups of coffee per day as heavy coffee drinkers. In the United States, coffee consumption is higher among men than women, and among smokers compared with non-smokers, but much lower among African Americans than among white Americans.
Tea
Tea consumption in the United States is increasing and varies considerably depending on the type of tea. In the U.S., 87% of total tea consumption is black tea, 12.5% is green tea, and the remainder consists of oolong and herbal teas.
Tea is preferred over coffee in Asia and in several South American countries (Argentina, Chile, Paraguay, Uruguay), which together account for 76.6% of global tea consumption.
Tea ranks second only to water as the most consumed beverage in the world, with total tea consumption being three times greater than coffee.
Additives
Coffee and black tea are often consumed with cream and/or sugar and/or milk. Non-dairy creamers often contain partially hydrogenated oils, which can be a significant dietary source of trans fats if used in large quantities. Added sugar can increase dietary glycemic load, potentially negating some of the benefits of caffeinated beverages. Sugar and non-dairy creamers may also reduce the antioxidant concentrations of these drinks.
It is unclear whether milk or other additives modify the health effects of coffee or tea.
Soft Drinks
Caffeinated soft drinks are another major source of caffeine intake, especially among children. Some sodas that are not typically associated with caffeine, such as certain lemon- and orange-flavored soft drinks, also contain caffeine.
Energy Drinks
Energy drinks are another form of caffeinated beverage. They typically contain about 100–200 mg of caffeine per serving, although some contain more. Male adolescents and young adults are the typical consumers.
Energy shots contain particularly high levels of caffeine (about 200 mg) due to their small volume.
Other Forms
Caffeine is also available as an over-the-counter drug and is frequently added to certain dietary supplements. Some supplements, particularly those marketed for workouts or weight loss, have been linked to various adverse events reported to the U.S. Food and Drug Administration (FDA). Caffeine is often a common ingredient in these products, and some cardiovascular side effects may be related to high caffeine doses. However, due to the nature of the FDA’s reporting system, these adverse events cannot be conclusively attributed to caffeine.
Caffeine powder, which is 100% pure caffeine, can lead to accidental overdose. Small amounts of caffeine are also found in chocolate- and coffee-flavored ice cream.
Specific Health Effects
The physiological and behavioral effects of caffeine depend on the dose, and research findings should be interpreted with this in mind. Moreover, epidemiological studies on caffeine are often confounded by other variables: healthier individuals are more likely to consume caffeine, and caffeine use is closely associated with tobacco use—therefore, tobacco exposure must be carefully controlled in both epidemiologic and experimental research.
Neuropsychiatric Effects
Caffeine has been shown to affect cognition and mood, both acutely and chronically. However, its effects vary depending on the study population, the amount of caffeine consumed, and the duration of use.
In resting individuals, low to moderate doses (30–300 mg) improve alertness and reaction time.
In sleep-deprived individuals, caffeine improves a wide range of functions, including learning, decision-making, and real-world tasks such as driving or flying.
Habitual consumers of coffee and tea perform better in various cognitive tests, such as reaction time and visuospatial reasoning.
Alertness
Caffeine consumption increases alertness, mental energy, and focus, especially when people are fatigued or working at night — likely the primary reason most humans consume caffeine regularly.
Caffeine mitigates the negative effects of sleep deprivation on a wide range of cognitive functions.
A systematic review of 13 randomized trials involving individuals with jet lag or shift-work disorder found that caffeine significantly improved concept formation, reasoning, memory, orientation, attention, and perception compared with placebo. It was also more effective than placebo in preventing errors and was similarly effective compared to other active interventions such as modafinil or bright light exposure.
Headache
Caffeine has pharmacological properties that can either relieve or trigger headaches. It has long been used for its analgesic properties and is often combined with other medications.
Randomized trials have found that combination drugs containing caffeine (such as aspirin, acetaminophen, and caffeine) are more effective for treating tension-type headaches and migraines than acetaminophen (Panadol) or low-dose ibuprofen alone.
Parkinson’s Disease
Studies have shown an inverse association between coffee or tea consumption and the risk of Parkinson’s disease, although the exact protective mechanism of caffeine remains unknown.
Alzheimer’s Disease
Few studies have examined the relationship between coffee and Alzheimer’s disease. A pooled analysis of two studies found that coffee consumption was associated with a small protective effect against Alzheimer’s disease.
Psychiatric Effects
Caffeine intake has been linked to a variety of psychological symptoms and disorders, though no causal relationship has been proven.
Acute caffeine intake is associated with anxiety, nervousness, insomnia, irritability, and even panic attacks in healthy volunteers.
Patients with pre-existing anxiety disorders may be more susceptible to caffeine’s anxiogenic effects.
Cardiovascular System
Low to moderate coffee consumption (up to three cups per day) may protect against myocardial infarction.
High coffee intake may cause arrhythmias in susceptible individuals, although coffee consumption is not a long-term risk factor for cardiomyopathy.
Drinking two or more cups of tea per day may also be associated with reduced risk of cardiovascular mortality.
Endocrine System
Caffeine consumption has been linked to a lower risk of diabetes, although causality has not been established.
Cancer
Most human data indicate no association between coffee or other caffeinated beverages and any type of cancer. Coffee and tea may reduce cancer risk due to their antioxidant properties, though findings remain inconsistent.
Osteoporosis
Data suggest that high coffee intake may be associated with lower bone mineral density and increased fracture risk in women, especially those with low calcium intake.
Conversely, tea consumption has been associated with higher bone density in several studies, although this increased density did not necessarily reduce fracture risk. The higher flavonoid content of tea, compared to coffee, is thought to contribute to bone mineral preservation.
Mortality
Many observational studies — though not all — have found an inverse relationship between coffee or tea consumption and overall mortality. One possible explanation is that healthier individuals are more likely to choose and consume caffeinated beverages than those who are ill.
Adverse Effects of Excessive Caffeine Intake
Excessive caffeine intake can lead to numerous adverse effects.
In an observational study of 217 individuals (average age 17) who contacted a poison control center after using caffeinated energy drinks, the most common non-serious adverse effects were palpitations, tremors, agitation, and gastrointestinal upset.
Less commonly, individuals exhibited serious neurological or cardiac signs (arrhythmias, ischemia, seizures, hallucinations).
More than 125 individuals were hospitalized for adverse effects, including 57 who had consumed caffeinated energy drinks alone.
Caffeine Withdrawal
Although early nonrandomized studies questioned the existence of a caffeine withdrawal syndrome, later randomized trials support its validity. A genetic predisposition to caffeine withdrawal has also been demonstrated.
A comprehensive review validated 10 symptom categories of caffeine withdrawal:
-
Headache
-
Fatigue/exhaustion
-
Decreased energy/activity
-
Reduced alertness/attention
-
Sleepiness/drowsiness
-
Reduced satisfaction/well-being
-
Depressed mood
-
Difficulty concentrating
-
Irritability
-
Vague/confused/unclear thinking