Some individuals break down caffeine within hours; others process it so slowly that a late-day cup can disrupt sleep.
According to reporting by National Geographic, Stanford neurologist Robert Cowan notes that inconsistent intake often leads to rebound symptoms such as headaches or restlessness.
That may explain why many people underestimate how sensitive they are to small changes in daily habits.
What caffeine actually does
Rather than simply “boosting energy,” caffeine interferes with the brain’s adenosine-signaling system, delaying sensations of fatigue.
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Robert Cowan told National Geographic that the brain adjusts quickly to regular use, which is why sudden withdrawal can leave people irritable and unusually tired.
Products and perceptions
The market now includes powders, gums, and concentrated drinks, making it harder to track how much we consume.
The U.S. Food and Drug Administration advises adults to stay below 400 milligrams per day, yet energy drinks commonly supply a quarter to half of that in a single can.
With multiple products in circulation, it doesn’t take much to reach the upper limit.
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Coffee and tea may offer antioxidants linked in several studies to lower rates of diabetes and liver disease, according to Stanford researcher Michael Fredericson.
Energy drinks, however, do not provide comparable benefits.
Vulnerable groups
Pregnant women are advised by the American College of Obstetricians and Gynecologists to keep intake below 200 milligrams daily.
Young people also face their own risks. National Geographic reports that many teenagers regularly drink energy beverages despite caffeine’s well-documented effects on sleep and cognition.
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Sources: National Geographic, Food and Toxicology, Food and Drug Administration og American College of Obstetricians and Gynecologists.
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