Caffeine is a chemical that occurs naturally in the leaves, grains, and fruits of several dozen plant species around the world. It is found in products such as tea, coffee, and many other nonalcoholic beverages. Caffeine is known for its stimulating effect, which is often used to combat fatigue or sleepiness, but it also causes insomnia in people highly sensitive to it.
Because caffeine enters the bloodstream relatively quickly, the psychostimulant effect occurs equally fast and can last several hours. Each person responds to caffeine differently, according to our metabolism, body mass, muscle mass, age, and sex. It’s been long believed that caffeine will dehydrate the body, but recent research demonstrates that although it has a small diuretic effect, it doesn’t cause dehydration.
Caffeine is absorbed along almost the entire length of the digestive system, from the stomach, through the small and large intestines, and in the rectum; it is metabolized in the liver. Total absorption into the blood occurs after about 45 minutes, and the maximum concentration in the blood serum can remain up to two or three hours after drinking it, although it varies individually.
The Food and Drug Administration states that 400 milligrams of caffeine per day is safe for an adult, which equates to 3 to 6 cups of coffee.
In the fermentation process of black tea (which lasts longer than other varieties), theaflavins and thearubigins are formed; these compounds have an equally beneficial effect on the body as the antioxidants found in green tea. Black tea is used to alleviate abdominal pain, and with honey and lemon it can relieve some symptoms of a head cold. Black tea’s caffeine content ranges from about 40 to 80 milligrams in a 12-ounce cup and depends on the species, the crop, the ripeness of the plant at harvest, and the fermentation method.
Green tea may be the variety most revered for its beneficial effects, particularly because it promotes weight loss, provides many antioxidants, and has some antibacterial properties. Green tea contains iron, zinc, potassium, sodium, and calcium as well as vitamins A, B, B2, B3, B6, C, E, and K. It will provide 40 to 60 milligrams of caffeine in a 12-ounce cup.
It is believed that drinking green tea promotes the stabilization of body weight and prevents the accumulation of fatty tissue. Studies on volunteers who for 12 weeks took a green tea extract rich in the antioxidant catechin had a significantly lower body mass and amount of adipose tissue (fat) compared to a control group.
A particularly noteworthy variety of red tea is pu-erh (or pu’er). Some studies have shown that this type of tea increases metabolism, resulting in the reduction of body fat. In one research effort, 88 percent of subjects drinking a few cups per day experienced a weight loss of 7–23 pounds while maintaining their current diet. Red tea has been found to support the liver, lower cholesterol, strengthen immunity, and help detoxify the body. It contains many healthy ingredients, such as tannins, alkaloids, flavonoids, minerals (calcium, magnesium, zinc, manganese, copper, selenium), and vitamin C. About 90 milligrams of caffeine are found in one 12-ounce cup.
White tea has been hailed as the elixir of youth because of its polyphenols—a group of antioxidants that fight free radicals. One cup of white tea contains 12 times more polyphenols than a glass of orange juice, which is also considered a rich source of these compounds. White tea also contains ample amounts of vitamin C and caffeine (30 to 40 milligrams), so it’s helpful for people who do intense mental work. The brew from this tea variety is a great alternative to coffee because it is in some ways healthier and it stimulates the body equally well, but it also reduces tension and stress.
Green coffee is simply coffee brewed with unroasted beans. It’s becoming increasingly popular—especially among people trying to lose extra weight. Studies have found that it supports health in several ways, such as aiding with weight loss, lowering blood pressure, and controlling blood sugar. It contains less caffeine than roasted beans (about 37 milligrams in a 12-ounce cup), and it provides a substantial amount of chlorogenic acid, which is the key source of green coffee’s beneficial properties. The lower caffeine content can also be beneficial, for example, for people with high blood pressure.
Green coffee also contains many antioxidants, which are very important for active people because training can increase the level of oxidation in the body. The presence of oxidants can harm muscles, increase catabolism, and thus limit your athletic capacity and performance.
Adapted from Sports Nutrition Handbook by Justyna Mizera, MA, and Krzysztof Mizera, PhD, with permission of VeloPress.