Jet lag is composed of a variety of unpleasant symptoms that vary with the number of time zones crossed, the individual, and even the direction flown (east versus west). The most typical symptoms include daytime sleepiness, fatigue, impaired alertness, and trouble initiating and maintaining sleep. Other symptoms of circadian dysrhythmia are insomnia, gastrointestinal complaints, apathy, weakness, irritability, malaise, and loss of appetite. Travel across time zones also has been associated with diabetic ketoacidosis, depression, and impaired cognitive performance in individuals at risk. Decreased sport performance has been noted in several studies.