**3. Jet Lag symptoms**

#### **3.1. Descriptive data**

Jet Lag symptoms are frequent. Rogers and Reilly [7] indicated that 74% of surveyed travelers reported some form of Jet Lag. Of these respondents, 50% reported above-average tiredness and fatigue and 28% indicated some disruption in normal sleeping patterns. And 5% reported difficulties in concentration, while 5% reported eating problems. Gisquet [8] reported 80% of sleep disorders among travelers: difficulty in falling asleep, insomnia, premature awakening and daytime sleepiness. Among very frequent travelers such as flight personnel and international business executives, the disorder may be recurrent or even chronic [9].

The most obvious Jet Lag symptoms for the majority of travelers are the inability to sleep during destination night and to remain alert during destination day. It also includes difficulty in concentrating, clumsiness, difficulty with memory, general weakness, dizziness and lethargy [10]. General malaise, dysphoric mood, headaches and gastrointestinal disorders (indigestion, loss of appetite, bowel irregularities) have also been described but cause less harm.

Symptoms logically vary according to the time of day where assessments are made. They will be lighter when day-time overlaps with a day-time at home (or when night-time overlaps with night-time at home). They will be worse when day-time is superimposed on night-time at home (sleepiness) or when night-time is superimposed on day-time at home (insomnia).

Morning-type people may find it more difficult to adjust westwards and evening-type people have more trouble traveling eastwards [11]. People with more rigid sleeping habits suffer more [12]. Short sleepers understandably adjust easier. Age over 60 results in greater difficulty in adjusting to Jet Lag [13]. Gender does not make a significant difference [14].

cardiovascular disease and female reproductive problems [23, 24]. The part played by Jet Lag in performance degradation and accidents has not been estimated precisely so far but might

Jet Lag

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http://dx.doi.org/10.5772/intechopen.75929

There are two main pathways followed by scientists to counter Jet Lag. Most studies have been performed by chronobiologists and have as their main goal to speed up the adjustment of the body clock to the new schedule, in particular using timed exposure and avoidance of bright light, as well as the timed use of the hormone melatonin. At the present time, chronobiologists have often succeeded in accelerating and thereby reducing the adjustment process. Their recommendations still make for a slow and not fully satisfactory result, especially when

The second school of research is more pragmatic. Here we start from the point of view that we want to be as fully operational as we can and as soon as possible. So the body clock is more or less left to itself and allowed to take its time without much interference. The aim is to counter insomnia and fatigue or sleepiness with substances that help sleeping and waking until the moment the adjustment is complete and the body clock has taken over. Obtaining enough sleep at more or less the right time, albeit somewhat artificial through the use of sleep inducers, is crucial to be in shape the next day, helping to adjust to Jet Lag, and is also far more comfortable than insomnia. On the other hand, fighting excessive daytime sleepiness has been studied in diseases that make people abnormally sleepy during the day, such as narcolepsy. This is not Jet Lag, although many symptoms are shared, but this information may be useful. However, the pragmatic approach has only been fully developed in the military, as they understandably need realistic answers to the issues of sleep, fatigue and vigilance, so that soldiers and pilots are at their best on the battlefield 365/24/7 if needed and do not risk their lives unduly because of lack of vigilance. The services need to control Jet Lag as fast as possible and have a long and valuable experience with drugs, from which civilians can prob-

Taking sleeping pills during flights and for a few days when at destination is in fact what many travelers do today, as an off-label (i.e., unapproved) treatment. This helps at least to obtain a subjectively better sleep, hopefully to be more awake the next day. Most people also use caffeine, some use alcohol and some even use stimulants. But most travelers do not know which medications to use, at which dosage and when to take them, in large part because one

be substantial.

**4. Remedies**

**4.1. General considerations**

many time zones are crossed.

ably benefit.

*4.1.2. What do people usually do?*

Jet Lag is not another Jet Lag.

*4.1.1. The chronobiologist and the military*

#### **3.2. Number of time zones crossed**

As could be expected, symptoms of Jet Lag are generally worse the more time zones are crossed. Although traveling over one to four time zones is not universally considered Jet Lag, I propose here to do so for the sake of consistency. If the normal sleep schedule is partly included in night-time at destination (more or less from ±1 to 7–8 h), there is at least some overlap with the usual sleeping hours: the problem will either be to have difficulties in keeping on sleeping (having flown westwards) or in falling asleep (eastwards) but some sleep will be found at least. When more than seven or eight time zones are crossed, then sleepiness will be experienced during the whole day and sleep will always be difficult to find at night. This spectrum of symptoms also explains why Jet Lag treatment standardization is difficult.

Flying west is usually considered easier in terms of Jet Lag. This is intuitive, as it is easier to stand some sleepiness late at night than trying to force oneself to sleep when there is no urge to do so. To almost fully adjust, and as a rule of thumb, it is generally considered that 1 day is needed for an hour eastwards, and 2 or 3 days for an hour westwards. Six hours eastwards (e.g., New York to Brussels) thus mean six days to adjust. Six hours westwards (Brussels to New York) mean 4 days. Above 8 h, time zone difference, it is not clear whether you will adjust by advancing or retarding the body clock and there may be individuals who do either one or the other [15].

#### **3.3. Sometimes severe adverse effects**

Jet Lag is usually medically benign and self-limited. It may though occasionally cause serious misjudgments in business and professional dealings. As mentioned above, it may ruin holidays, especially if they are of short duration. Athletes will not perform at their highest level if the timing of contests does not coincide with their circadian peak and training occurs at inappropriate times [16].

But Jet Lag can sometimes be a more serious health issue. Loss of sleep is usually translated into excessive daytime sleepiness, and sleepiness is clearly associated with reduced performance and cognitive reaction time [17, 18]. Pilots on long-haul east-west flights have, for instance, been shown to microsleep during the "cruise" phase of a flight and even during the critical transition from the cruise phase to the descent phase, the point at which the planned descent to final approach altitude is initiated [19].

Countermeasures, such as controlled short cockpit naps, crew alternation or alertness monitoring have been proposed [20]. It has been estimated that 21.9% of all road accidents are related to sleepiness in general [21]. Business people have been observed to function at only 80% of their perception after traveling [22]. Studies in shift workers, who also suffer repeated episodes of dyssynchrony, suggest even more severe consequences, including rates of cancer, cardiovascular disease and female reproductive problems [23, 24]. The part played by Jet Lag in performance degradation and accidents has not been estimated precisely so far but might be substantial.
