University of Iowa Health Science Relations and
Lisa Casas, R.D., L.D.
First Published: June 2004
Last Revised: June 2004
Peer Review Status: Internally Peer Reviewed
Whether it's coffee, tea, or soft drinks, most of us consume caffeine at some point in our day.
"It helps people stay alert and stay focused," says Lisa Casas, R.D., L.D., a clinical dietitian at University of Iowa Hospitals and Clinics. But the effects of caffeine don't last for long. "It really doesn't stay in the system very long--it's only about two to three hours before it is excreted from the body," she says.
A naturally occurring substance, caffeine is a common component in many leaves, seeds, and fruits. Foods and beverages derived from these plants will contain caffeine. Common sources of caffeine include coffee, tea, and some soft drinks. Caffeine is also present in chocolate and in energy drinks like Red Bull.
Most people should stick to a moderate amount of caffeine, which translates to around 300 milligrams (mg) of caffeine in a day.
Here are some of the most common foods and beverages containing caffeine along with their caffeine amounts.
- an eight-ounce brewed coffee has anywhere from 60 to 120 mg of caffeine depending on how it is brewed
- an eight-ounce serving of brewed tea has between 20 to 90 mg
- an eight-ounce serving of a soft drink with caffeine has 20 to 40 mg
- an ounce of milk chocolate has 6 mg
According to Casas, there are many myths associated with caffeine consumption. For one thing, caffeine does not cause dehydration. "The amount of liquid consumed with caffeine will likely compensate for any diuretic effects associated with it," she says.
Because it may act as a mild stimulant to the central nervous system, some may classify caffeine as addictive. Not so, says Casas. "It's nowhere near comparable to a drug or tobacco addiction."
A sudden decrease in caffeine consumption may cause some individuals to experience mild symptoms of withdrawal such as drowsiness, fatigue, or headaches. However, Casas says, those symptoms will usually subside within a day or two.
Recent studies have determined that moderate amounts (less than 300 mg) of caffeine are not harmful during pregnancy. If you are pregnant or if you have high blood pressure or heart disease, you may wish to consult your physician to determine the appropriate amount of caffeine that you should consume.