A U.S. new study shows that citrus-flavoured sodas often have a higher caffeine content than the most popular colas.

The research also found that caffeine content can vary widely from brand to brand, and even within a brand. The study's researchers, along with consumer advocates, say labels on packaging should give the caffeine content to help buyers make informed choices.

Coca-Cola and PepsiCo are in the process of adding caffeine labels to their cans.
(Mark Lennihan/Associated Press)

"I don't really take a stand on whether caffeine is good or bad, but I do think the consumer has a right to know what they're getting," said Leonard Bell, one of two food researchers who conducted the study at Auburn University in Alabama.

The Food and Drug Administration does not limit the amount of caffeine in foods. FDA spokeswoman Veronica Castro said a 0.02 per cent caffeine content is generally recognized as safe for cola-type beverages. For a 340-millilitre soft drink, that's about 72 milligrams of caffeine.

In Canada, caffeine cannot be added to clear sodas or juices. Health Canada says minor side effects of caffeine range from alertness and improved concentration to insomnia, headaches, irritability and nervousness. The federal agency recommends that healthy adults should consume a maximum of 450 mg of caffeine daily, the equivalent of three 237 ml cups of brewed coffee.

The study by Bell and co-author Ken-Hong Chou found caffeine content in 340-millilitre sodas ranged from 4.9 milligrams for a store brand of cola to 74 milligrams in Vault Zero, a citrus drink.

David Schardt, senior nutritionist at the Center for Science in the Public Interest, said the Washington-based nonprofit first asked the FDA 10 years ago to require that food and drink labels show the caffeine content.

"People should be able to monitor their intake and to make informed choices because it can affect their sleep and can make some people jittery," Schardt said.

The FDA has received a number of petitions to include caffeine content labelling on products, including the 1997 request from the consumer group, according to Mike Herndon, another FDA spokesman.

Coca-Cola, PepsiCo phasing in caffeine labels

The Coca-Cola Co., based in Atlanta, and Purchase, N.Y.-based PepsiCo Inc. said they are phasing in new labels that include caffeine content. Most national brands also provide lists of the amount of caffeine in their products on their websites.

While caffeine occurs naturally in some products, like coffee and tea, it's an additive in soft drinks. It is commonly sought out for its stimulatory effect, and beverage companies say the slightly bitter substance is also an element in their flavour formulas.

Bell and Chou say the buzz caused by caffeine is its main draw. They said previous research showed that only eight per cent of adults were able to differentiate between the taste of caffeinated and caffeine-free colas.

Their study analyzed the caffeine contents of 56 national brand and 75 store brand carbonated drinks. It was published in the August issue of the Journal of Food Science.

Caffeine content of well-known national brands include:

• Coca-Cola (33.9 milligrams).
• Diet Pepsi (36.7 milligrams).
• Pepsi (38.9 milligrams).
• Dr Pepper (42.6 milligrams).
• Diet Dr Pepper (44.1 milligrams).
• Diet Coke (46.3 milligrams).
• Mountain Dew (54.8 milligrams).
• Diet Mountain Dew (55.2 milligrams).

By comparison, according to the American Beverage Association website, a 340-millilitre cup of coffee has between 156 and 288 milligrams of caffeine, and the same amount of tea has 30-135 milligrams.

Bell said the data provided by manufacturers of national brand soft drinks was consistent with the findings of his study. He said the caffeine data for store brand drinks is not easy to find and often isn't available at all.