Sunday, June 22, 2003

By Michael Woods, Post-Gazette National Bureau

WASHINGTON -- Graveyard shift is the evocative term, dating from the early 20th century, for late-night work when the rest of the world is quiet as a cemetery.

The 21st century is opening with new medical evidence that working that shift may be a fast-track to the grave, putting some workers -- especially women -- at high risk for serious diseases.

A few weeks ago, for instance, a Journal of the National Cancer Institute study of 78,586 women found that night shift workers have a 35 percent increased risk of colorectal cancer. It bolstered findings of two other studies that found that women night shift workers have a risk of breast cancer up to 60 percent higher than those who never worked nights.

Studies show night shift workers are at high risk for other health problems, too, including heart disease, workplace accidents, automobile accidents and stomach problems.

They've even become namesakes for a new disease, Shift Work Sleep Disorder. Symptoms include excessive sleepiness, insomnia, headaches and difficulty in concentrating. It affects 70 percent of all shift workers, according to one estimate.

"I think there are reasons for concern regarding the health of night shift workers," said Dr. Timothy H. Monk, an international authority who directs the University of Pittsburgh Medical Center's human chronobiology research center.

"My experience is that employers do not supply enough information to employees about surviving shift work," said Dr. James Blessman, of Wayne State University, in Michigan, an occupational medicine specialist.

"I suspect that we are paying a hefty price in decreased productivity and the cost of ill health in the United States because many people don't get enough sleep."

The price may mount as the global economy and other factors entice more people into a 24/7 lifestyle -- working, shopping and partying at hours unthinkable a generation or two ago.

About 10 percent of all U.S. companies currently operate around the clock, according to the U. S. Department of Labor. More than 15 million Americans work outside the traditional 9-to-5 shift.

The number of people working an evening, night or rotating shift rose by about one-third between 1985 and 1997. Part of the increase resulted from services catering to society's new nocturnal bent: 24-hour hot lines for technical support or emergency health care; more mail order and online companies; and all-night retail stores, photocopy centers and eateries.

In addition, society's most famous group of night owls -- teenagers and young adults -- is on a growth spurt. This bunch, who love to be awake when older folks sleep, may almost double by mid-century.

"As our culture moves to a 24-hour/7-day-a-week operation and the number of shift workers and teens continues to climb, the problem could worsen if changes are not made now," Dr. Ricardo Martinez warned back in 1999.

At the time, Martinez was chief of the National Highway Traffic Safety Administration, which, along with the National Institutes of Health, was calling on Congress to pay more attention to drowsiness-related highway accidents among shift workers and teenagers. The annual roadway toll is 1,550 deaths and 40,000 serious injuries.

"People with insufficient sleep suffer impairments in performance, attention and reaction time, which leads to errors, including automobile crashes," said Dr. Claude Lenfant, of the National Institutes of Health. "We must make the American public more aware of the importance of adequate sleep, as well as the risks of insufficient sleep."

The agencies prepared educational materials for high school students, employers and shift workers. But little has changed in society at large. The number of shift workers, along with the scientific evidence that shift work causes health problems, continues to grow.

European countries have taken concrete steps, noted Monk, a professor of psychiatry. Regulations in the European Union limit the number of night shifts employees can work and provide for mandatory days off. "They're ahead of us in terms of monitoring shift workers' health," as well, he said.

Companies that operate around the clock divide a 24-hour day into thirds, with workers assigned to each shift. They often run from 7 a.m.-- 3 p.m.; 3 p.m.--11 p.m.; and 11 p.m.-7 a.m.

Some employees are permanently assigned to work outside the traditional day shift. Although it takes time, their circadian rhythms -- the body's natural 24-hour cycle of sleep and wakefulness -- usually adjust.

Many more employees, however, rotate through the three shifts, alternating days and nights. They have more problems sleeping during the day, staying awake at work at night and avoiding accidents.

Early in June, Harvard University researchers reported that women who work rotating night shifts have a 35 percent higher risk of developing cancer of the colon and rectum. Colorectal cancer is the third most common type in men and women, with about 147,000 new cases and 57,000 deaths annually.

Dr. Eva S. Schernhammer and her associates studied data gathered since 1976 from 78,586 nurses, comparing cancer risk among day shift and night shift workers.

An almost-identical 2001 Harvard study noted a similar increase in breast cancer risk, as did a study done at the Fred Hutchinson Cancer Research Center in Seattle, which found a 60 percent increased risk of breast cancer in women who worked the graveyard shift. The risk increased with each additional hour per week on the night shift.

"The findings from our current study, together with previous reports on increased breast cancer risk among night workers, clearly are alarming," Schernhammer said. "There is no reason to believe that the results for colorectal cancer would not also apply for men."

The prime suspect linking night work and cancer is melatonin, a hormone produced in the brain. Melatonin production peaks during sleep between 1-2 a.m. Nighttime sleep deprivation or exposure to bright light interrupts melatonin production.

When melatonin levels drop, a woman's ovaries kick out more estrogen, a hormone known to promote breast cancer. Melatonin also slows the growth of cancer cells.

Monk cautioned, however, that melatonin may not be the only factor, or even the main factor.

"There's a lot more going on among night shift workers than melatonin," he said. "The links between cancer and night work are likely to be very complex, involving sleep loss, stress and other factors."