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August 1, 1999
By: Andrea Platzman, R.D.
Today, more than 80% of Americans ingest caffeine every day, with an average intake of about 200 mg.
"Caffeine is a naturally occurring substance found in tea, coffee and cocoa that has physiological responses in humans," states Manfred Kroger, Ph.D., professor of food science, The Pennsylvania State University, University Park. Caffeine belongs to a group of compounds known as methylxanthines; its chemical name is 1,3,7-trimethylxanthine.
Although the FDA classified caffeine as GRAS in 1958, extensive research has been conducted on its health aspects during the past two decades. Most agree, however, that caffeine does not cause any adverse health effects with moderate consumption - 300 mg, or three cups of coffee each day. Even pregnant women can safely consume this amount, says Kroger.
Health myths and truths
Osteoporosis. Caffeine can be hard on bones, leading to a greater chance of developing osteoporosis later in life. With every 6-oz. coffee serving or 2 cans of caffeinated soda consumed, about 5 mg of calcium are excreted in the urine. The more caffeine a woman consumes (related studies haven't yet been conducted on men), the greater the calcium loss, and the greater the potential bone damage.
Birth defects and miscarriages. In 1980, based largely on animal studies linking caffeine to birth defects and miscarriages, the FDA advised pregnant women to avoid caffeine-containing foods and drugs, or to consume them sparingly. Although birth defects were never shown at the levels Americans typically consume, most pregnant women avoid caffeine.
Heart disease. "Caffeine is safe for consumption for people with heart disease. Often it is the blood chemistry and the mixture of phenols and the hundreds of other substances found in coffee and not the caffeine that have been implicated," states Kroger.
Cafestol and kahweol, two substances found in the oils in ground coffee, raise low-density lipoprotein (LDL, or "bad") cholesterol levels. These substances are removed in instant or filtered drip coffee, but boiled coffee, French press and espresso contain them in abundance.
In a recent study, researchers at Duke University Medical Center, Durham, NC, found that those who consume four to five cups of coffee throughout the morning experience stress-like symptoms that last into the evening. These symptoms include an average 32% increase in adrenaline, a 14% increase in noradrenaline and a three-point increase in blood pressure. Over time, these stresses can weaken the immune system and lead to heart damage.
Cancer. In the 1980s, researchers concluded that coffee use might account for a substantial proportion of the pancreatic cancer cases in the United States. However, all of the follow-up studies dispelled this conclusion.
Gallstones. A study published in June 1999 in The Journal of the American Medical Association reported that men who drank two to three cups of coffee per day had a 40% lower risk of gallstones than non-coffee drinkers, and those who drank four or more cups per day lowered the risk by 45%. This occurs because coffee with caffeine stimulates contractions in the gallbladder, and lowers levels of gallstone-producing bile cholesterol.
Athletes and caffeine
Competitive athletes have used caffeine as an ergogenic aid, or a performance-enhancing substance, for decades. While not all studies agree, most describe enhanced endurance and delayed fatigue in both recreational and elite athletes who ingest 3 mg to 9 mg of caffeine per kg of body weight prior to engaging in prolonged endurance and intense short-term exercise.
Although the exact mechanisms of caffeine's beneficial effects are unclear, there are several theories on the subject. Caffeine appears to inhibit the action of phosphodiesterase - an enzyme that hydrolyzes cyclic adenosine monophosphate (cAMP) - and thus raise the levels of cAMP. Raised levels of cAMP result in neural excitation and subsequent stimulation of the central nervous system, thereby reducing the onset of fatigue.
Another theory proposes that caffeine has a positive effect during endurance exercise due to an elevation of catecholamines, which enhance fat oxidation. This is of utmost importance during prolonged moderate to high intensity exercise, because as soon as glycogen stores become depleted, fat stores are necessary for longer-duration exercise.
Experts recommend that athletes who choose to use caffeine consume no more than 3 mg to 6 mg per kg of body weight per day. "One cup (of coffee) may be good; however, three cups may not be as good because of the diuretic effect," says Kroger. Caffeinated beverages tend to increase liquid excretion via urination, so it's important to continually replenish bodily fluids by drinking water or other non-diuretic beverages.
Whether caffeine intake is good, bad or inconsequential to overall health seems to vary from person to person, although most experts feel caffeine is safe in moderation.
Andrea D. Platzman is a registered dietitian who is a consultant to the food industry, and regularly writes for nutrition publications. She earned a master's degree in nutrition from New York University, and has a culinary and business background.
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