By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Caffeine is a powerful central nervous system stimulant found in coffee, most teas, chocolate, cocoa, energy drinks and colas. But the amounts of it in a beverage or food can vary greatly. For instance, an espresso has more caffeine than instant coffee, and dark chocolate has more caffeine than milk chocolate.
Similarly, caffeine is present in ground coffee in amounts ranging from 0.75-1.5% by weight. The content in teas averages about 40 milligrams, but it varies greatly depending on the strength of the tea. There are also about 40 milligrams of caffeine in 12 ounces of a carbonated cola.
About 85% of U.S. adults consume about 135 milligrams of caffeine daily, equivalent to one 12-ounce cup of coffee. Up to 400 milligrams per day is generally safe for healthy adults, which is roughly equivalent to four cups of brewed coffee, 10 cans of cola or two “energy shot” drinks.
How the Human Body Processes Caffeinated Foods and Beverages
After consumption, the caffeine in beverages and foods is absorbed rapidly and reaches its peak concentration in the bloodstream in about 45-60 minutes. About 3% or less of it is excreted in the urine.
The half-life of caffeine is typically about four to five hours, but it can range from one and a half to nine hours, depending on genetic factors related to metabolic rate in the liver. The absorption rate can also be affected if it is taken with medications such as oral contraceptives. Smokers have massively increased clearance, meaning it stays around in their systems for a shorter length of time.
Caffeine’s Use in Sports
Caffeine has a long history of use by athletes in both endurance and power sports with lots of controversy surrounding its potential benefits versus its disadvantages. Some studies have shown that it enhances endurance by enabling muscle cells to burn more fat, thus preserving the body’s stores of carbohydrate. Moderate ingestion of caffeine mobilizes free fatty acids from adipose tissue (storage cells for fat) into the blood, thus making fat more readily available.
Because sustaining a high-exercise intensity in endurance events such as a marathon is very dependent upon maintaining stores of carbohydrate in muscle cells (called glycogen), utilizing more fat will theoretically spare carbohydrate reserves and prolong the time before an athlete reaches exhaustion. Athletes in power sports have also utilized caffeine, which many advocates claim enhances strength and reaction time, probably by affecting the calcium-dependent process of fast-twitch muscle fiber contraction.
Caffeine circulating within the body is absorbed into tissues that have the highest water content, namely skeletal muscle cells. It also penetrates the blood-brain barrier quickly, which initially causes an increase in mental alertness.
Later, however, a reduction in mental alertness is often seen in athletes. Vivarin alertness pills and Dexatrim weight-control pills contain about 200 milligrams of caffeine per pill and are often abused by powerlifters.
Caffeine intake is restricted (but not totally banned) by the National Collegiate Athletic Association (NCAA). Urine concentrations of caffeine up to 15 micrograms per milliliter are permitted by the NCAA, which equates to about 500 milligrams of caffeine taken about two to three hours before an athletic event. With a cup of coffee containing about 135 milligrams, this amount of caffeine would be equivalent to about four cups of coffee, depending on the dosage in the coffee.
In children, this amount would be equivalent to a child consuming two 12-ounce cans of a caffeinated carbonated beverage. For instance, Coca-Cola, Pepsi and Mountain Dew have very high levels of caffeine – about 69 milligrams per 12 ounces.
Herbal teas, chocolate and cocoa products contain the caffeine derivative theobromine. Athletes should also be aware that most prescription medications and over 2,000 nonprescription drugs such as pain relievers and cold remedies contain caffeine. Using medication containing caffeine could cause some athletes to be disqualified from athletic events, even though they were not deliberately attempting to cheat by loading up on caffeine.
The Placebo Effect and Caffeine Consumption
Even though numerous athletes regularly consume caffeine during training and competition, several studies have indicated that mild to moderate consumption may not enhance athletic performance as much as previously thought. Some well-controlled (double-blind) scientific studies have found that the only benefit that mild to moderate doses of caffeine provide is the simple placebo effect.
A placebo improves performance through the power of suggestion. For instance, if an athlete really believes it will work, it possibly will. Incidentally, this placebo effect has also been demonstrated in an experiment. Test subjects were given placebo tablets and told that the tablets were an anabolic steroid. They later displayed increases in strength.
The Dangers of Overconsumption
On the negative side, high levels of caffeine can cause headaches, nervous irritability and insomnia. Overconsumption may also lead to physiological and psychological addiction and withdrawal symptoms. Additionally, it may increase the risk of osteoporosis (bone loss) and cause abnormal heartbeats (arrhythmia).
Pregnant or breastfeeding women, as well as children, need to restrict their intake. Adolescents and young adults also need to be aware that excessive caffeine intake and mixing it with alcohol and other drugs is never good. One teaspoon of powdered caffeine is equivalent to about 28 cups of coffee, which can create serious health problems and possibly even death.
Drinking the Appropriate Amount of Caffeine Has Some Health Benefits
Caffeine in appropriate doses, however, has antioxidant and anti-inflammatory properties. In addition, it may decrease depression because it stimulates the production of dopamine, a brain chemical that enhances pleasure, motivation and learning. Low levels of dopamine create feelings of being tired, moody and unmotivated.
There Should Be More Public Awareness of Caffeine’s Harmful Side Effects
You are not alone if you rely on caffeine to keep you alert and improve your concentration during both daily activities and sports competitions. One of the most widely used and abused drugs in the world, caffeine has been shown to enhance performance in some athletes. However, there needs to be more awareness of its negative side effects and the legal restrictions that are now being enforced during some athletic competitions.