An estimated 80% to 90% of Americans say they use caffeine daily.
Caffeine can be found in more than 200 foods (such as chocolate), drinks (such as coffee, tea and soft drinks) and over-the-counter medicines (such as aspirin).
One of every two people say they have at least one cup of coffee each day, typically in the morning to help them wake up. An average cup of brewed coffee contains 100 to 150 mg of caffeine, and a cup of brewed tea can have nearly the same amount.
A 1.5-ounce milk-chocolate bar has about 10 mg of caffeine, and many soft drinks have 30 to 40 mg of caffeine or more per 12-ounce serving.
Those hooked on coffee will tell you that it helps to suppress their appetite and makes them feel more energized during the day. Why? Caffeine is a drug that stimulates the central nervous system. Unlike alcohol, which is a depressant, caffeine is a mood elevator.
While it increases levels of serotonin -- a calming neurotransmitter -- it also links to specific receptors on the surface of brain cells that are normally reserved for another naturally occurring, calming neurotransmitter called adenosine.
When caffeine is there in place of adenosine, the brain becomes more reactive to stimulants, such as noise and light, which is why a person often feels more alert and talkative after consuming caffeine.
Experts do not agree on the safety of caffeine or its impact on health or exercise performance. However, studies have shown increases in the force of the heartbeat, higher levels of stress hormones, increased breathing and heart rates and temporarily elevated blood pressure.
Critics who believe caffeine is safe argue that problems occur only in those who are hypersensitive, unaccustomed to it or who consume extremely large amounts.
The majority of scientific evidence seems to show that for many healthy adults, moderate quantities of caffeine (250 to 350 mgs per day) pose no significant health risks.
However, a link between consuming higher amounts and certain heart problems, such as arrhythmias, has been reported.
Extremely high intake (150 milligrams per 2.2 pounds of body weight) can create an overdose effect, which is very dangerous and, in rare cases, can be fatal.
To those who are at risk, even moderate intake can create symptoms of overdose.
Initial caffeine overdose symptoms include flushed face, frequent urination, shakiness, rapid heartbeat, vomiting, sleep disturbances and upset stomach.
The more severe cases also can include symptoms such as acute mental confusion and visual disturbances.
We know that caffeine interacts with certain medications, can interfere with iron absorption and causes urinary excretion of calcium.
It can interfere with sleep quality, increases urine production, increases amounts of fatty acids in the blood and increases production of stomach acid.
Caffeine is a diuretic; it causes water loss from the body. To help offset this loss, try to drink an extra glass of water for each cup of caffeinated beverage you consume.
If you are pregnant, anemic, have digestive or heart problems or other medical conditions, ask your doctor for appropriate guidelines concerning use of caffeine.
Caffeine is metabolized and expelled by the body, so it does not get stored or accumulate in the bloodstream. It is absorbed quickly from the stomach and peaks in the bloodstream in one or two hours.
For the average person consuming 100 mg, it takes roughly five to seven hours to metabolize half of this. Until all of the caffeine has been processed, the central nervous system continues to be stimulated.
Most people experience symptoms of withdrawal without their usual doses of caffeine.
After looking at more than 170 years of research on caffeine withdrawal, a study at Johns Hopkins University suggests that true caffeine addiction and withdrawal symptoms can occur from drinking as little as one cup of coffee per day.
If you are trying to cut back or stop your use of caffeine, it is normally advised to gradually wean yourself rather than going cold turkey.
Stopping abruptly tends to exaggerate withdrawal symptoms such as depressed mood, irritability, anxiety, upset stomach and headaches.
Going cold turkey also produces a rebound effect in which the body becomes hypersensitive to its own natural sleep-enhancer, adenosine. When this happens, adenosine has an even more powerful sleep-enhancing effect, making you feel tired and sluggish and causing blood pressure to drop.
Withdrawal symptoms usually begin in as little as 12 hours after the last dose of caffeine, typically peak within one to two days and can last up to a week or even longer.
(c) 2004 Marjie Gilliam
Marjie Gilliam is an International Sports Sciences Association master certified personal trainer and fitness consultant. She owns Custom Fitness Personal Training Services. Reach her by e-mail at OHTrainer@aol.com. Her Web site is marjie.hypermart.net.