Our Earth is divided into 24 time zones. A time zone corresponds to a time change of 1 hour. Starting at the prime meridian, crossing Greenwich, there are 12 time zones to the East and 12 to the West.

Various biological functions follow endogenous or daily rhythms. Physiological and psychological regulation are based on these rhythms.

The most important examples are:

• regulation of the sleep-awake-rhythm;
• blood pressure and pulse frequency regulation;
• regulation of the body temperature;
• secretion regulation of gastric acid, hormones, melatonine, electrolytes

Flights through various time zones disrupt this rhythm in different ways, which may give rise to jet lag symptoms.

Jet lag is a series of symptoms caused by disturbance of the endogenous rhythms after crossing more than 2-3 time zones. The main symptoms are sleeping disturbances and their consequences - tiredness, concentration problems or loss.

Jet lag symptoms occur at varying intensities and depend on a series of factors:

• Age - persons of older age feel the symptoms more intensively;
• Social factors - private problems, marital crisis, financial worries, etc. have an influence on sleep and intensify the jet lag feeling;
• Flight direction - on Eastbound flights the jet lag feeling strikes more severely; there is no jet lag on N-S/S-N flights;
• Flight time - day flights are usually easier to deal with in both directions.

According a common formula, a daily adjustment of 50 % can be expected. Therefore, after 3 days there is an adjustment of 87,5 % to the new local conditions. In spite of the adaptable sleep-awake-rhythm, the leading jet lag symptoms are sleeping difficulties; these are interrupted sleep processes with prolonged periods of falling asleep and troubles with sleeping through the night. Frequent nightly wake ups, tiredness and moodswings during the day are usual.

For short-term stays it is recommendable to keep the home rhythm. For longer stays the immediate adjustment to the local hour is recommended. It is also advisable to change the bed time before traveling about an hour, beginning approx. three days prior to departure.

• Westbound flights - 1 hour later each day
• Eastbound flights - 1 hour earlier each day

• dark room
• earplugs
• put an additional alarm clock (to avoid anxiety of missing an appointment)
• sleep supporting measures
• fitness exercises before going to bed, hot shower or bath afterwards
• supply of quickly absorbing carbohydrates before going to bed (milk with honey, glass of beer, bedtime sweets)
• relaxation through self-hypnosis
• sleeping aids like valerian tea
• medication or melatonine preparations only after medical consultation
• Pills might be medically necessary, especially when serious difficulties to adapt engender long-lasting insomnia, making sleeping for the concerned person an absolute must for health reasons. Here again a medical consultation is required.

Melatonine is a substance similar to hormones, which is produced in the brain by the pineal body close to the pituitary gland (hypophysis). Darkness stimulus produces an increased release of melatonine into the blood, light stimulus causes a jam in the melatonine release.

When examining melatonine or its metabolism products, scientists found out that they have hypnotic effects leading to sleepiness. In the USA melatonine is registered as food and is therefore available in all drugstores. In Europe melatonine is considered a medicine because of its influence on the vegetative nerve system and is neither available nor registered as a medicine.