As a nurse, i worked many evening, night and double shifts in hospitals. My friends and I were obsessed with our sleep, or lack of it: How long did you sleep? Was it good? The body’s circadian rhythm — an internal biological clock that regulates a variety of functions — is easily interrupted by this kind of shift work, as well as by travel across time zones.

Circadian rhythms, modulated by the hypothalamus of the brain, play an integral role in our sleep-wake cycle. These rhythms are directly affected by light, which sets the biological clock, but can also be altered by almost any kind of stimulus, such as the beeping of an alarm clock or the timing of meals.

Crossing time zones temporarily throws off circadian rhythms, causing symptoms of jet lag. The severity of these symptoms is related to the direction of travel (more frequent with eastward travel) and the number of time zones crossed (at its worst when crossing three or more zones). “Time travelers” are familiar with the resulting fatigue and insomnia, but symptoms of jet lag can also include anxiety, dehydration, headache, irritability, coordination problems and even memory loss.

Symptoms similar to those of jet lag are common in people who work nights or work in shifts. Because their wake time conflicts with powerful sleep-regulating cues such as sunlight, they often become uncontrollably drowsy during work and may have difficulty falling asleep during their off time.

Sleep is vital to our physical and mental health. Insufficient sleep has been linked to the development of a number of chronic conditions, including diabetes, cardiovascular disease, obesity and depression. Inadequate sleep can also affect the immune system, decreasing our ability to fight disease and endure sickness. It can lead to impairment of memory and physical performance and even reduce our ability to concentrate or perform mathematical calculations. Studies have revealed an association between short sleep duration and excess body weight. If sleep deprivation continues, confusion, hallucinations and mood swings may develop.

Experienced travelers know that when they cross over several time zones, it may take a few days to overcome these symptoms. To fend off the groggy effects, try to adapt to the new time zone before you depart. Go to bed earlier at night if you are traveling east and stay up later if you are traveling west. It is helpful to choose daytime flights, ideally with an afternoon or evening arrival in your country of destination. Note, however, that if you are flying north or south within the same time zone, you will not experience jet lag despite the long distance.

For shift workers, rapid shift changes and shift changes in the counterclockwise direction are most likely to cause symptoms of a circadian rhythm disorder. Light, higher noise levels and elevated room temperature are environmental factors that are not conducive to good sleep and should be avoided by shift and night workers.

Simple lifestyle strategies can promote healthy sleep. First, check your medications — many can cause insomnia, so ask your doctor or pharmacist about the drugs you take. There is little evidence that supplements and over-the-counter sleep aids are effective, and, in some cases, there are safety concerns. Check the labels to see if they contain caffeine or other stimulants such as pseudoephedrine. Light therapy may be helpful for travelers suffering from severe jet lag, shift workers and night workers. If you experience difficulty sleeping for more than a month, you should contact your doctor. For more information, visit http://www.sleepfoundation.org.

Foundations for good sleep

• Go to bed and get up around the same time each day.
• Make your bed a resting place, not a media center.
• Say no to naps; you won’t sleep as well at night.
• Use a fan or white noise generator to mask noises.
• Sleep in loose, comfortable clothing in a comfortable bed.
• Maintain a cool temperature in your bedroom.
• Reduce nicotine and caffeine consumption during the day.
• Avoid heavy meals before bedtime.
• Drink warm milk before bed.
• Decrease or eliminate alcohol consumption.
• Exercise daily but not four to six hours before bedtime.
• If you read before bed, do it in another room sitting in a chair.
• Sleep in a separate bed or room if your partner keeps you awake.