Study: Caffeine May Add Zing to Cola, But It Doesn't Add Flavor

From the WebMD Archives

Aug. 14, 2000 -- Soda manufacturers are usually the folks who set up taste tests, but recently some researchers from Johns Hopkins University turned the tables on the soda industry by performing a decidedly different kind of taste test.

In the study, which used Coke products, only two out of 25 hard-core cola drinkers were able in a blind taste test to detect whether a soda sample contained caffeine. The results seem to cast doubt on claims made by soft drink manufacturers that caffeine, a proven addictive, mood-altering drug, is present in soft drinks only as a flavor enhancer, suggest the researchers.

A beverage industry publication says that Americans in 1998 drank 15 billion gallons of carbonated soft drinks, or the equivalent of 585 12-ounce cans for every person in the country. To put it another way, that's enough liquid to cover an area of approximately 46,000 acres to the depth of one foot. About 70% of the soda downed in the U.S. has caffeine as an added ingredient. Web sites of major soda manufacturers play up the fact, though, that typical colas contain about a third of the caffeine found in a cup of brewed coffee.

The web sites also claim that caffeine is added as a flavor enhancer. Pepsi's site states that "caffeine provides a characteristic flavor to soft drinks." And, according to a document posted in the "Frequently Asked Questions" section on the Coca-Cola Company's web site, "caffeine that is added to Coca-Cola classic, diet Coke and the other products in which it is used is for flavor purposes only. We use only the amount necessary to achieve the appropriate optimum flavor profile for the particular product sold."

Tobacco companies made the same claims about nicotine for many years, notes study author Roland R. Griffiths, PhD, professor of psychiatry and neuroscience at the Johns Hopkins University School of Medicine in Baltimore.

"It is valuable for the general public, the medical community, and regulatory agencies to recognize that high rates of consumption of caffeinated soft drinks more likely reflects the mood-altering and physical dependence-producing effects of caffeine, as a central nervous system-active drug, than its subtle effect as a flavoring agent," write Griffiths and co-author Ellen M. Vernotica, PhD, in an article in the August issue of the journal Archives of Family Medicine.


The comparison of cola with tobacco, however, angers members of the National Soft Drink Association (NSDA), a trade group representing soft drink makers, marketers, and distributors.

"The author's personal conclusion that the industry's marketing efforts of products which contain caffeine 'strongly parallels' nicotine is irresponsible. Every major independent health organization, including the National Institutes of Health, the American Medical Association, [and] the U.S. Food and Drug Administration, tells consumers that moderate consumption of caffeine is safe," NSDA spokesman Jeff Nedelman is quoted as saying in a press release criticizing the study.

Griffiths tells WebMD, "Caffeine is the most widely consumed psychoactive -- mood altering -- drug in the world. At doses that are delivered in a can of soft drink, it produces mood and behavioral effects. Those mood effects are well known to most consumers of caffeine, and they include things like increased sense of well-being, increased alertness, concentration, some increased sociability, and decreased sleepiness."

The downside, however, is that daily consumption of caffeine in doses equivalent to two to three cans of soft drinks a day produces physical dependence, indicated by withdrawal symptoms when caffeine users try to go cold turkey, Griffiths adds. Characteristic symptoms of caffeine withdrawal include headache, tiredness, lethargy, and sometimes irritability; in extreme cases, people can have flu-like symptoms, nausea, and vomiting.

"We also know that the development of physical dependence is intimately linked to the continued daily administration of compounds that contain caffeine, so that most people who are regular consumers of caffeine are waking up in the morning and taking caffeine, experiencing the elevation in mood, and not recognizing that by not having caffeine overnight, they're actually in a low-grade withdrawal state. Caffeine is suppressing low-grade withdrawal symptoms, and it's that mechanism that is so important to the [regular use of the product]," Griffiths says.

In their study, Griffiths and Vernotica recruited volunteers who reported drinking cola at least once a week, and who expressed a preference for a specific brand of cola based on flavor and caffeine content. The prospective tasters were secretly screened for their ability to distinguish between regular and diet Coke; subjects who couldn't tell the difference (seven of 32) were then excluded.


The researchers then put the remaining 25 participants through six tasting sessions in which the concentration of caffeine in the drinks was increased. All sessions used cola from the same batch, and each consisted of 25 trials in which tasters compared two samples of cola solution labeled "A" and "B."

For the first five trials of each session, the tasters were put through their paces in a "warm-up," in which they were informed about whether they were tasting sample A or B as a means of heightening awareness of flavor differences (they were not, however, told which contained caffeine). The study subjects then downed each of two samples, with each tasting separated by a rinse with bottled spring water.

At the lowest caffeine concentration, none of the tasters could tell the difference between the two samples. At a level of caffeine similar to or slightly higher than that found in either Coke classic or Pepsi, only two of the 25 were able to discriminate between the caffeinated and decaffeinated versions. It wasn't until tasting colas with caffeine concentrations far above those allowed by the FDA that the remainder of the subjects began noticing a difference.

In its response, the NSDA asserts that 25 people is too small a test group to draw any meaningful conclusions. But, as Griffiths tells WebMD, "almost all of the taste studies that have reported taste-detection thresholds with caffeine have been done with sample sizes smaller than 25, including studies that the soft drink industry cites to support their claim [that caffeine improves the flavor of the soft drink]."

The NSDA also claims that by taking 50 samples at one sitting, the tasters might have suffered from "flavor fatigue," and that the six participants who were cigarette smokers "should have been disqualified because most smokers have desensitized taste buds."

"Too few people were tested, too little science was used in the testing and too much opinion is contained in the conclusions," Nedelman says in the written statement. "This is an exercise in scientific self-promotion, not a meaningful presentation of scientific evidence. It is yet another personal attack on the industry by a researcher who has a personal axe to grind when it comes to caffeine."


Griffiths tells WebMD that he isn't calling for a ban on caffeine, but that he does support recommendations for more accurate labeling of caffeine on food products. "That's really the message to physicians and consumers alike: Caffeine really is a mood-altering drug, and people need to be informed about it and accord it respect, [and] come to understand how it affects them when they take it and when they fail to take it."