The safe daily limit for caffeine in adults is commonly cited as 400 mg. Consistently surpassing this threshold can lead to an overdose with potentially serious health effects, particularly for individuals with heart conditions and for children.
In practical terms, a 30 ml shot of espresso typically contains about 60–70 mg of caffeine, while a cup of weak black or green tea averages around 40 mg. This translates to a practical guideline of not exceeding roughly five cups of coffee or ten cups of tea in a day, depending on the strength of the brew and individual sensitivity.
Caffeine acts as a stimulant on the nervous system; it can increase alertness, improve concentration, and elevate mood. However, when intake is excessive, those positive effects can diminish and eventually become harmful, as the body struggles to adapt to the heightened stimulation.
Indicators of caffeine overdose include chills, headaches, nausea, tremors, rapid heart rate, excessive sweating, dizziness, cramps, and diarrhea. For minor symptoms, simple measures such as staying well hydrated, taking a light walk, and temporarily reducing caffeine intake can help. More pronounced or persistent symptoms warrant medical evaluation to prevent complications.
Excess caffeine carries real risks for certain groups. It can pose serious concerns for children and adolescents as well as people with cardiovascular or kidney conditions. Overdoses are more common with energy drinks and caffeine tablets, where a single serving may deliver around 200 mg of caffeine and often contains additional ingredients that can amplify effects.
Some researchers have noted that low-calorie beverages containing caffeine, such as plain tea or coffee without added dairy, may influence metabolic processes and fat metabolism. While these observations suggest a potential link between caffeine and changes in energy expenditure, they are not a universal guarantee of weight loss and should be considered alongside overall diet and activity.