We've known for years that a shifting sleep schedule can lead to many health problems, but more recent studies have shown us why. Disrupted sleep can actually alter your genes. In fact, altered genes are part ofthe mechanism of cancer formation. As such, having an out of sync body clock has been compared to a carcinogen.

This is certainly bad news for the many police officers, firefighters, medical personnel, convenience store clerks, third shift workers and others who work when the rest of us are sleeping. Many of these people find that they struggle with feeling tired at the wrong times and having energy when they need to be resting.

University of Surrey researchers found shifting sleep from night to day disrupts the normal functioning of about a third of our genes. In fact, the new study discovered that sleep shifting has a more destructive impact on gene activity than sleep deprivation. Recently published in the journal Proceedings of the National Academy of Sciences, the study offers new clues to sleep's critical importance in maintaining good health and preventing chronic diseases.

Although the British study was narrow in scope, involving just 22 volunteers over a three-day period -- its findings are intriguing and could have important health implications for people who suffer disruptions to their circadian rhythm due to work shifts, jet lag, pregnancy, medication or changes in their daily sleep routine.

In the study, researchers reset participants' body clocks. Sleep cycles were shifted by 12 hours so the major sleep period occurred from noon to 6:30 p.m. Daily blood samples allowed researchers to observe changes in gene activity and what they saw was surprising. Resetting the body's clock caused a massive drop in the number of genes synched to the body's natural circadian rhythm.

So why is it important for gene activity to be in synch with our circadian rhythm? Genes govern the production of proteins, which control virtually every chemical signal, hormone and biologic function in the body. The timing of protein production is critical and must coincide with our behaviors and activities for optimal functioning.

Here is a graphic showing how your body clock affects your daily functioning.

Not only is your level of alertness regulated by your body clock, but certain digestive functions and other physiologic processes occur at certain times based on your body timing. If you shift your sleep times back and forth such that it becomes out of sync with your body's natural rhythm, you can get physiologic processes that are performing at times they should not. For example, you may have less optimal digestion of food if you're eating at night instead of during the day when your body is normally geared to burn fuel.

It's still unclear what about shift work causes the alteration in genes. Is it the light exposure at night? Is it the sleep deprivation that can come with shifting schedules?

So what's a person to do if you have to work a night shift?

Generally I recommend that people working shifts minimize shifting back and forth between time schedules and instead remain on one shift. If you have a day off in between your shifts, stay on your night schedule.

Suppose you are off for one week and want to join your family for vacation? Staying awake all day can work for day one, but often times people take several days to recuperate from shifting their sleep to a day schedule. You don't want to lose half of your vacation adjusting your sleep.

Light therapy is a powerful tool you can use to shift your sleep times. Here is a short video showing you how to do it.

One last tip:

Once you return to your night schedule, you may have trouble being alert those first few nights. To improve your alertness, you can do the following:

Before your shift

Take a one- to two-hour nap three hours before your shift.

When you wake to prepare for your shift, use light therapy for 15 to 30 minutes.

Start of shift

Drink 200 mg of caffeine.

Use light therapy for 15 to 30 minutes.

Night shift work has many negative consequences to your health, including altering genes that control body functions. It may be these changes that are responsible for the diseases we see in people with poor sleep due to shift work. In addition to these long-term effects, shifting your sleep has a more immediate impact on how you feel and function. If you are unable to change your work time, you can still minimize the short-term negative effects of shifting your sleep schedule with behavioral interventions such as light therapy, keeping a consistent shift, moderate caffeine consumption and scheduled naps.