Table 3.2 in Chapter 3 shows the per capita consumption of beverages: milk, tea, coffee, bottled water, carbonated soft drinks, fruit juices and fruit drinks, canned iced tea, and vegetable juices. Consumption of carbonated soft drinks generally rose between 1966 and the early 1990s and then leveled off somewhat. Most carbonated soft drinks contain caffeine. Coffee consumption was relatively stable from 1966 through 1976, dropped sharply in 1977, and has stayed somewhat consistent since then with the lowest level of consumption in the mid-1990s. In 2003 coffee consumption was 24.3 gallons per person.
Tea consumption rose somewhat steadily from 1966 through the mid-1970s, somewhat stabilized until 1990, and then rose sharply in the early-to-mid-1990s to somewhat stabilize again. In the mid-1990s, when coffee consumption was down somewhat, tea consumption was up somewhat. In 2003 tea consumption was 7.6 gallons per person.
The average daily intake of caffeine among consumers in the United States is about 280 mg, which is equal to about three cups of coffee or about seven twelve-ounce glasses of a cola beverage (L. M. Juliano and R. R. Griffiths, "A Critical Review of Caffeine Withdrawal: Empirical Validation of Symptoms and Signs, Incidence, Severity, and Associated Features," Psychopharmacology, vol. 176, 2004).
Results of a study published in 2001 (Janet Brown et al., "Misclassification of Exposure: Coffee as a Surrogate for Caffeine Intake," American Journal of Epidemiology, no. 153) show that the four main sources of caffeine for people aged thirty to seventy-five living in southern Ontario, Canada, were brewed coffee, instant coffee, regular tea, and cola soft drinks. Brewed coffee was the main source of caffeine, while tea and cola soft drinks ranked second or third, depending on age. Cola drinks ranked second for those aged thirty to forty-four, and tea ranked second for those aged forty-five to seventy-five. Men had a higher caffeine intake than women, and those aged forty-five to fifty-nine had a higher caffeine intake than younger persons.
Results of a study on beverage caffeine intake in U.S. consumers (C. A. Knight et al., Food and Chemical Toxicology, vol. 42, no. 12, December 2004) were some-what consistent with the Ontario study. Research results revealed that children and young adults up to age twenty-four consumed most of their caffeine in carbonated soft drinks. Consumption of coffee generally did not begin until age fifteen, but children as young as one year old consumed tea. People ages twenty-five and older consumed most of their caffeine in coffee, with carbonated soft drinks a second choice, and tea in third place. When people reached fifty years of age or so, tea became their second-largest source of caffeine, with carbonated soft drinks their third. This "switch" between tea and soft drinks remained throughout the rest of their lives.
The Ontario study also showed that caffeine intake is usually underestimated because people often report only their coffee intake and omit caffeine from other sources. The results of this study showed an average intake of caffeine for subgroups of these Ontario residents to range from a low of 288 mg per day for women ages thirty to forty-four to a high of 426 mg per day for men ages forty-five to fifty-nine.
Coffee remains the major source of caffeine for adults. According to the National Coffee Association's 2003 National Coffee Drinking Trends survey, 51% of the adult population drinks coffee everyday, representing 108.3 million coffee drinkers. Another 28% of the population, or 58.3 million adults, drinks coffee occasionally.
Only a small percentage of eighteen-to-twenty-four-year-olds consumed coffee in 2003—just 7% as estimated by the National Coffee Association. High levels of unemployment are correlated with lower levels of
coffee drinking; this age group had the highest level of unemployment of all adults in 2003.