Health
Understanding Caffeine: Half-Life and Safe Limits
Ahoxy Health Team
What is Caffeine Half-Life?
The "half-life" of a substance is the time it takes for the amount of that substance in your body to be reduced by half. For the average adult, the half-life of caffeine is approximately 5 hours.
What does this mean?
If you drink a cup of coffee with 100mg of caffeine at 4:00 PM:
- 9:00 PM: You still have ~50mg in your system.
- 2:00 AM: You still have ~25mg in your system.
This implies that afternoon coffee can significantly disrupt your sleep, even if you feel "fine" by bedtime.
Safe Limits
The FDA and other health organizations generally cite 400 milligrams a day as an amount not generally associated with dangerous, negative effects for healthy adults.
Approximate Caffeine Content
- Brewed Coffee (8 oz): 95 mg
- Espresso (1 shot): 63 mg
- Black Tea (8 oz): 47 mg
- Coke/Pepsi (12 oz): 30-40 mg
- Energy Drinks: 80-200+ mg (varies widely)
Factors Affecting Metabolism
- Age: Metabolism slows with age.
- Genetics: Some people are "slow metabolizers" due to the CYP1A2 gene.
- Pregnancy: Caffeine metabolism slows significantly during pregnancy (half-life can extend to 10-18 hours).
- Smoking: Smokers metabolize caffeine twice as fast.