It’s All in Your Head

What is the size of a grain of rice and tells you that it’s time to go to bed?

It’s your suprachiasmatic nucleus (SCN), a cluster of cells located in the hypothalamus.

Although small, it does a lot for its size. It tells you when to sleep, wake up and eat. It controls the fluctuations of body temperature, blood pressure and cardiac output. It even regulates the secretion of several hormones, including seratonin and melatonin.

An Internal Clock

The SCN influences just about all of our physiological functions, which can vary greatly based on the time of day. For example, blood pressure is generally higher in the morning. Cyclical variations are called circadian rhythms.

The SCN has a large sphere of influence, but like a benevolent ruler, it allows itself to be influenced by its subjects. Individuals’ circadian rhythms can thus adapt to various external signals. The principal ones are sleep, activity, meals, melatonin and, most importantly, light. All these stimuli help regulate the organism.

A Traveler Forewarned

People tend to have problems with their circadian rhythms when they travel. In changing time zones, a person loses track of his habitual landmarks. Most notable is the day-night cycle, which can cause the well-known problem of jet lag: fatigue, sleeping problems, loss of concentration and constipation.

There are ways to facilitate that adaptation. For instance, you can adopt the time of your destination a few days in advance. Within reason, adjust your sleeping hours and mealtimes to reflect those of your destination country. At the very least, once on the plane, adjust your watch to the time it is over there. Finally, expose yourself to sunlight or light panels before you leave and after you arrive in order to accelerate the resynchronization of your rhythms.

Always be sure to drink plenty of water while traveling by plane—1 cup (8 fluid ounces) for every hour of flight—to prevent dehydration. The level of humidity in the cabin is only about 10 percent. It’s better to avoid alcoholic or caffeinated drinks, since they are diuretics.

The direction of your flight can have an effect as well; it has been shown that travel from east to west is more tiring. It’s also worth mentioning that north-south (or south-north) trips don’t have any effect on circadian rhythms, because there isn’t any change in time zones.

A New Science

Over the last 30 years, the discovery of circadian rhythms has given birth to a new medical science: chronotherapy. Research has shown that time is an important factor in the administration of about 60 different medicines. For example, chemotherapy is more effective and triggers fewer undesirable reactions if administered in the late afternoon rather than in the early morning.