Published online ahead of print publication in the Journal of Food Science, the study examines sodas in three primary categories: colas, pepper-like beverages, and citrus beverages.
Most national brands were found to be higher in caffeine content than store brands. In addition, citrus beverages were found to contain the highest caffeine levels compared to other categories. Diet sodas contained higher levels of the compound compared to their regular counterparts.
Caffeine, an odorless, bitter substance present in certain plants, is found naturally in extracts derived from these plants, such as coffee or tea. But it is also added intentionally as an ingredient to many carbonated drinks for its stimulatory effect.
However, widespread consumption - often uniformed or unintentional - has led to the compound drawing increased attention over the years. Government bodies have specified the maximum levels allowed in sodas: in the US, the Food and Drug Administration (FDA) sets the limit at 0.02 percent, or 72mg/12oz; Canada sets limits in cola-type beverages of 200ppm, or 71mg/12oz; Australia sets limits of 51mg/12oz; and limits in New Zealand are 71mg/12oz.
The American Dietetic Association - as well as the Food Standards Agency in the UK - advises people not to consume more than 300mg of caffeine per day. Health Canada advises consumers to limit their caffeine intake to 400 to 450 mg per day. This advice is particularly aimed at pregnant women, who, studies indicate, have greater risk of miscarriage or babies with low birth weight if they exceed the 300mg barrier.
According to researchers of the current study, "without caffeine values placed on the label, consumers are left relatively uninformed regarding the amount of caffeine contained in these beverages. In addition, comprehensive databases on the caffeine contents of specific carbonated beverages are lacking".
"Therefore, the specific objective of this research project was to measure the caffeine contents of national and private-label store-brand carbonated beverages so that current data will be available to the scientific community and public."
The researchers analyzed 56 varieties of national-brand and 75 private-label store brand carbonated beverages. Average caffeine contents of each carbonated beverage were determined from a minimum of 2 different lots. The beverages analyzed in this study were purchased between June 2005 and July 2006.
Some of the more common national-brand carbonated beverages analyzed
included Coca-Cola, Pepsi, Dr Pepper, Mountain Dew, and their diet varieties. Store brands examined included products from Wal-Mart, Kroger and Winn-Dixie's. Overall caffeine contents ranged from 4.9mg/12oz to 74mg/12oz.
In national-brand colas, the highest value (57.1 mg/12 oz) was found in Pepsi One. Except for the lower caffeine contents of Ritz Cola and Red Rock Cola and the higher caffeine content of Pepsi One, the remaining samples contained 33.3 to 48.1 mg caffeine/12 oz.
The caffeine contents of 10 national-brand pepper-type beverages ranged from 39.4mg/12oz (Cherry Vanilla Dr Pepper) to 44.1mg/12 oz (Diet Dr Pepper).
For citrus beverages, the range was 19.7 to 74.0mg/12oz.The greatest caffeine content (74.0mg/12 oz) was found in Vault Zero. Except for the lowest caffeine content of Faygo Moon Mist (19.7mg/12 oz), the other beverages contained more than 49mg caffeine per 12 oz.
Out of the private-label store brands tested, caffeine contents of regular colas ranged from 4.9mg to 46.4mg/12 oz. Diet colas had levels ranging from 10.3mg to 61.9mg. Private-label pepper-type sodas had levels ranging from 18.2 to 59.8 mg/12 oz. For citrus drinks, the range was 25.1 to 55.1 mg/12 oz.
These findings reveal that as well store brands generally containing less caffeine than national brands, they also showed a wider content range, which often varied between different lots of the same drinks. These deviations, said the study, point to less stringent quality control with store-brand products than with the national-brand products.
The findings also show that the overall caffeine averages for the regular beverages were close to the values set out in the USDA nutrient database. Contrary to this result, the average caffeine contents of the diet drinks were lower than listed by USDA.
"Our data may be used to update and expand the USDA nutrient database so that consumers have more current and accurate information," wrote the researchers.
"However, the best way for universal access to caffeine data is to place values on food labels so all consumers can be better informed about the amount of caffeine they are ingesting," they concluded.
In February this year, both Coca-Cola and PepsiCo announced their intent to place caffeine contents on the labels of various carbonated beverages.
Source: Journal of Food Science
Published online ahead of print. doi: 10.1111/j.1750-3841.2007.00414.x
"Caffeine Content of Prepackaged National-Brand and Private-Label carbonated Beverages"
Authors: K.H. Chou and L.N. Bell