Did you know that fluctuations in our environment, such as light and temperature, can dictate our internal clocks and alter our ability to function properly? That’s why jet lag symptoms arise when we travel to another time zone. Coordinated daily rhythms are evident in most aspects of our physiology, and they’re driven by internal timing systems that are known as circadian rhythms.
Several studies have shown that jet lag causes sleep disturbances because humans are very sensitive to changes in their temporal setting. The most common jet lag symptoms, including sleepiness, decreased efficiency and premature awakening, can be reduced by taking actions to help the body adapt to its new environment.
What Is Jet Lag?
Jet lag is also known as circadian desynchrony. Desynchrony is a condition in which the environmental cues and patterns conflict with an individual’s existing pattern. And that’s exactly what’s going on when we experience jet lag — there’s a mismatch with the body’s natural circadian rhythm and the external environment as a result of travel across time zones.
In order to fully understand what happens to the body when experiencing jet lag, you must first understand the role of the internal circadian clock. The central circadian clock is located in the suprachiasmatic nucleus of the hypothalamus. This is where light signals from the retina are received. The suprachiasmatic nucleus is responsible for adapting the circadian rhythm according to the light-dark cycles of the environment and generating neuronal and hormonal activities that regulate various body functions in a 24-hour cycle.
The suprachiasmatic nucleus initiates the actions of the pineal gland, which starts to make melatonin that’s released into the bloodstream. Within the pineal gland, serotonin, a neurotransmitter that’s derived from the amino acid tryptophan, is processed to yield melatonin. When melatonin levels increase, we begin to feel more sleepy, and when our circadian rhythms are running normally, melatonin levels remain elevated while we sleep for approximately 12 hours. Then melatonin levels drop again in the morning, remaining that way throughout the day.
Daily rhythms are evident in most aspects of our physiology, and they’re driven by our internal timing systems, or circadian clocks. Our environment provides rhythmic cues, called zeitgebers, that synchronize the internal body clock to the Earth’s 24-hour light-dark cycle. Although light is the strongest environmental cue received by the body, other cues include temperature, meal timing, social interaction, exercise and even the effects of medication.
This explains why blind people typically have “free-running” sleep/wake cycles, which can be extremely burdensome if a synchronizing treatment is not applied. Because they have no perception of light, their endocrine, metabolic, behavioral and sleep patterns are inconsistent.
Jet Lag Symptoms and Causes
The jet lag syndrome emerged with the rise of long-distance air travel. Travel fatigue is different than jet lag, but both conditions have similar symptoms. Because long flights are often tiring and uncomfortable, and the dry cabin air contributes to dehydration, it may require some rest for your body to bounce back. Travel fatigue can be an issue whether or not you travel across time zones. Jet lag, on the other hand, happens because your body is no longer synchronized to the environment’s rhythms.
Symptoms of jet lag may include:
loss of concentration
decreased ability to perform mental and physical tasks
difficulty initiating and maintaining sleep at night
Jet lag symptoms affect all age groups, but they may have more pronounced effects on the elderly, whose recovery takes longer than that of young adults. A 1999 study conducted at Harvard Medical School found that people over 60 years old have less regular circadian rhythms, lower body temperatures and melatonin rhythms, and greater difficulty coping with jet lag, especially when traveling eastward.
The direction of travel affects the severity of jet lag symptoms. Travel across time zones, especially eastward, disrupts daytime rhythms. When we travel eastward, the length of day is shortened, and the circadian system must also shorten to re-establish a normal cycle. This makes jet lag and sleep disturbances worse after eastward flights than after westward flights.
Research published in Neuroscience Letters indicates that your chronotype (how you perform at different times of day) may also influence how you’re affected by jet lag. Data suggests that morning-type people who prefer to wake up early have less difficulty flying eastward, while evening-type people who prefer to wake up late have less difficulty flying westward.
Sleep disturbances usually last a few days, but they can persist for as long as one week if the change in time zones is greater than eight hours. Research shows that the rate of adjustment to the new time zone is typically equal to one day for each time zone crossed.
The goal of treatment is to speed up your body’s ability to shift the phase of your body clock from the time zone you just left to the new zone. Measures that don’t include medications are best because they allow for the environmental cues to push the circadian phase toward the rhythm of light and dark at the new destination.
Although jet lag symptoms usually last only a few days, research shows that jet lag carries potential to lead to long-term consequences. A 2006 study published in Current Biology found that chronic jet lag increased mortality in aged mice. After 56 days of six-hour adjustments of the light cycle, only 47 percent of the mice survived.
Another study assessed the contribution of occupational factors to breast cancer risk among cabin attendants in Finland. The data showed that sleep rhythm disruptions were positively related to risk of breast cancer, although the associations were statistically nonsignificant.
Other symptoms of ongoing jet lag may include cognitive deficits, gastrointestinal disturbances, infertility and heart disease.