The timing of sleep in relation to the body’s natural rhythm has been under recognized as a health issue, said Dr. David J. Earnest, a professor in neuroscience and experimental therapeutics at Texas A&M College of Medicine in College Station.

Much of Earnest’s research has focused on the 24-hour cycle, circadian rhythms - the body’s biological clock.

“What has come to light over the last five to 10 years is that there are a number of sleep issues beyond insomnia that are a concern,” Earnest said.

The issues relate to the timing of sleep and its implications in various health problems, he said.

The modern world has managed to complicate something that is very natural. People are spending more time working, trying to remain competitive in the job market. The industrialization of the work force and the shift work that followed has caused problems.

The timing of sleep is very important, Earnest said, and a statistical study on humans in Europe uncovered a connection between nurses who worked night shifts with certain types of cancers, especially breast cancer.

“It’s not as though they are getting less sleep, but it’s the timing of their sleep,” he said. “Most are rotating on to a shift for four or five days and then off for a couple of days.”

While working at night, the nurses will sleep during the day, but on days off they will change their sleep pattern to accommodate family and society.

“What we have known for a long time is when timing of sleep is changed, as with shift workers, performance is affected,” Earnest said.

It’s like having jet lag most of the time and the body remains stressed because it’s continuously trying to adjust to a new sleep cycle.

A couple of notable examples of accidents and their implications to errors in human performance are the Exxon Valdez oil spill in Alaska and the Chernobyl nuclear plant accident in Russia, he said.

Errors in performance are most likely when workers are rotating from one shift to another, Earnest said. The Valdez ship’s captain had been drinking, which adds to the problem in terms of human performance, but he also had gone through a change in shift schedule. The reactor explosion at Chernobyl nuclear plant in Russia happened at 3 a.m.

Some industries have made changes in how to manage people who work at different times of the day.

The airline industry, up until about 10 years ago, had pilots on alternating shifts with no set pattern for when a pilot would sleep or fly, causing a lot of potential for accidents and errors, he said. The industry since adopted a more consistent organization and planning schedule for pilots and flight attendants.

“The other industry that has compensated, to a degree, is medical,” Earnest said.

Medical residents in the past had to work up to 72-hour rotations and, in addition to being sleep deprived, they were not in the best position to provide optimal performance.

The amount of time allotted to sleep and the timing of that sleep became an important factor, he said. Now, the rotations are not as long and the time for sleep is scheduled more carefully.

“Hospitals, like many industries, have to have people working at night, but at least there has been a recognition of the problem,” Earnest said.

The science

Ten years ago, researchers like Earnest were focusing on an area of the brain called the suprachiasmatic nucleus, a pair of pinhead-sized brain structures. This is the location of the master clock and it was thought to drive all of the circadian rhythms throughout the body.

“What has come to light, has made the picture more complex and exciting,” Earnest said. “Pretty much all cells and tissues throughout the body function as local clocks.”

It was much simpler, he said, when it was thought there was a clock in the brain that sent signals out and regulated rhythms.

The issues are different now and there are additional questions, Earnest said.

How do the clocks in the tissues maintain local time and what happens when things go awry and you lose track of local time? What kind of signal does the master clock use to synchronize all of the other clocks through the light/dark cycle and maintain order?

Now, as researchers look at the issues of the shift worker, the connection of circadian rhythms, the disruption of those rhythms and the various kinds of cancer, they will need to understand what’s going on in the local clocks as well as the clock in the brain, Earnest said.

“We’re looking for the signals that provide communication between individual tissues and individual cells in a particular organ, as well as the signals the master clock uses to synchronize for the light/dark cycle,” Earnest said.

During the 20 years Earnest has been studying circadian rhythms and its implications, the field has come a long way.

The health implications have become apparent in the last 10 to 15 years. Now there have been connections with metabolic syndromes, various types of cancers and other health disorders, particularly depression and seasonal affective disorder.

Earnest believes more will be uncovered that links irregularity of circadian rhythms with other health disorders.

It’s not only important for the human body to be synchronized, not only externally, but internally as well. When that internal order is disrupted, things begin to fall apart.