However, its addition was contested with claims that this diagnostic model of caffeine addiction is not supported by evidence. The American Psychiatric Associations DSM-5 does not include the diagnosis of a caffeine addiction but proposes criteria for the disorder for more study. Dependence and withdrawal
Withdrawal can cause mild to clinically significant distress or impairment in daily functioning. The frequency at which this occurs is self-reported at 11%, but in lab tests only half of the people who report withdrawal actually experience it, casting doubt on many claims of dependence. Mild physical dependence and withdrawal symptoms may occur upon abstinence, with greater than 100 mg caffeine per day, although these symptoms last no longer than a day. Some symptoms associated with psychological dependence may also occur during withdrawal. The diagnostic criteria for caffeine withdrawal require a previous prolonged daily use of caffeine. Following 24 hours of a marked reduction in consumption, a minimum of 3 of these signs or symptoms is required to meet withdrawal criteria: difficulty concentrating, depressed mood/irritability, flu-like symptoms, headache, and fatigue. Additionally, the signs and symptoms must disrupt important areas of functioning and are not associated with effects of another condition.The ICD-11 includes caffeine dependence as a distinct diagnostic category, which closely mirrors the DSM-5s proposed set of criteria for "caffeine-use disorder". Caffeine use disorder refers to dependence on caffeine characterized by failure to control caffeine consumption despite negative physiological consequences.
Physical performance
Caffeine is a proven ergogenic aid in humans. Caffeine improves athletic performance in aerobic (especially endurance sports) and anaerobic conditions. Moderate doses of caffeine (around 5 mg/kg) can improve sprint performance, cycling and running time trial performance, endurance (i.e., it delays the onset of muscle fatigue and central fatigue), and cycling power output. Caffeine increases basal metabolic rate in adults. Caffeine ingestion prior to aerobic exercise increases fat oxidation, particularly in persons with low physical fitness.Caffeine improves muscular strength and power, and may enhance muscular endurance. Caffeine also enhances performance on anaerobic tests. Caffeine consumption before constant load exercise is associated with reduced perceived exertion. While this effect is not present during exercise-to-exhaustion exercise, performance is significantly enhanced. This is congruent with caffeine reducing perceived exertion, because exercise-to-exhaustion should end at the same point of fatigue. Caffeine also improves power output and reduces time to completion in aerobic time trials, an effect positively (but not exclusively) associated with longer duration exercise. Specific populations
Adults
For the general population of healthy adults, Health Canada advises a daily intake of no more than 400 mg. This limit was found to be safe by a 2017 systematic review on caffeine toxicology. Children
In healthy children, moderate caffeine intake under 400 mg produces effects that are "modest and typically innocuous". As early as 6 months old, infants can metabolize caffeine at the same rate as that of adults. Higher doses of caffeine (>400 mg) can cause physiological, psychological and behavioral harm, particularly for children with psychiatric or cardiac conditions.