**2. Nutritional caffeine intake**

Today, individuals consume low or high levels of caffeine, often knowingly and sometimes unknowingly. Since the production and consumption of caffeine-containing foods vary by country, society and individual, it is quite difficult to accurately calculate individuals' nutritional intake of caffeine. **Table 2** shows caffeine levels in certain foods which are frequently consumed by the general population and considered to be important in terms of caffeine content.

Caffeine is very common in nature, and coffee, tea, energy drinks, chocolate, and cocoa are accepted as sources of nutritional caffeine intake [22]. Caffeine levels in these foods vary according to content, ratio between tea/coffee and water, brewing time and other consumption characteristics [23, 24]. In general, coffee has a higher caffeine level than other foods. As for tea groups, the caffeine level of black tea is higher than other tea types. Caffeine levels are usually at a certain level in soft drinks such as cola and energy drinks as they have standard prescriptions and production techniques. The caffeine level in chocolate varies according to the amount of cocoa it contains. Coffee is also known as the source of nutritional caffeine of adults throughout Europe, especially in Finland, Denmark, Sweden and Switzerland. In all member states of the European Union, there is a "high levels of caffeine" warning on beverage labels containing more than 150 mg/L of caffeine [25].


Many institutions and researchers try to estimate nutritional caffeine intake by examining dietary habits of individuals. The number of studies conducted in this area is quite large and the findings of some studies are given below.

#### **Table 2.**

*Caffeine levels in some foods [11, 18–21].*

FDA states that a daily intake of 400 mg of caffeine can be considered safe for healthy adults. On the other hand, it has declared that some individuals may be negatively affected by lower doses of caffeine, and studies will begin to investigate the safety of caffeine added to foods, with particular emphasis on children and adolescents [18]. Health Canada has specified safe daily caffeine intake for healthy adults and pregnant women as ≥400 mg/day and <300 mg/day, respectively. The same institution has reported that daily caffeine intake for children of different age groups is in the range of 45 to 85 mg/day (45 mg/day for 4–6 years, 62.5 mg/day for 7–9 years, and 85 mg/day for 10–12 years) [26].

In a study conducted in America with 24,808 individuals between 2001 and 2010, it was reported that more than 85% of adults (≥19 years of age) regularly consumed caffeine and that their average daily caffeine intake was 180 mg/day. In the same study, highest and lowest intake of caffeine was detected in males between the ages of 31 and 50 and females between the ages of 19 and 30, respectively, the caffeine intake of males (211 mg/day) was more than females (161 mg/day), and 98% of the daily caffeine intake came from beverages. The drinks that cause caffeine intake are as follows: coffee by 64%, carbonated soft drinks by 18%, tea by 16%, and energy drinks by less than 1% [27].

In a study examining the daily caffeine intake of adolescents living in the United States between 1999 and 2011, it was reported that more than half of the children at ages ranging from 2.5 to 5 and about 75% of children over the age of 5 consumed caffeine on a daily basis. The mean daily caffeine intakes of children between the ages of 2 and 11 and adolescents between the ages of 12 and 17 were determined as and 50 mg/day, respectively. It was reported that the source of caffeine was carbonated soft drinks for children under the age of 12 and coffee for children that were 12 and older [28].

In another study, daily caffeine intake was calculated as 15, 26, 61, 213, and 135 mg/day for the general population who were 4–8, 9–13, 14–19, and 51–70 years old and those who were 4 years old or younger, respectively. The daily caffeine intake is higher in males (196 mg/day) than females (151 mg/day). Although the distribution of the drinks that cause daily caffeine intake varies by age, the largest contribution is from coffee (64%) and tea (18%) [29].

In another study conducted in the United States, daily caffeine intake was calculated as 120 mg/day (1.73 mg/kg body weight/day) for all age groups. The highest caffeine intake was in individuals in the 35–49 age range (170 mg/day). Daily caffeine intake in pregnant women was estimated to be 58 mg/day. According to the other findings of the study, the daily caffeine intake was calculated as 14 mg/day (0.82 mg/kg body weight/ day), 22 mg/day (0.85 mg/kg body weight/day), and 106 mg/day (1.54 mg/kg body weight/day) for ages ranging from 1 to 5, 6 to 9, and 20 to 24, respectively. It was pointed out that the main source of caffeine was coffee in adults and soft drinks in young people. Tea ranked second in both groups [30].

Australian Children's Nutrition and Physical Activity Survey determined the general daily caffeine intake as 18 mg/day in a study on caffeine consumption of 4487 children and adolescents between the ages of 2 and 16 in 2007. The mean daily caffeine intake by age groups was determined as 3, 8, 19, and 42 mg/day for ages ranging from 2 to 3, 4 to 8, 9 to 13, and 14 to 16, respectively. It was stated that the main source of caffeine was drinks (81%) and that the highest contribution was made by soft drinks (31%), coffee (21%) and tea (17%), respectively [31].

In a study conducted in Italy on 1213 adolescents (12–19 years), it was found that 76% of individuals consumed caffeine on a daily basis and the daily caffeine intake was approximately 125 mg/day (2.1 mg/kg body weight/day) [32] while the daily caffeine intake was calculated as 79 mg/day and coffee, tea, and soft drinks were

listed as the beverages with the highest contribution to the daily caffeine intake in a study conducted in England on 2008 individuals of varying ages [33].
