DEAR DOCTOR K:
I’m a nurse, and I can be assigned to work the day shift, evening shift or night shift. I hear that shift workers can develop health problems. What is known about that?
More than 9 million people in the United States are shift workers like you. Studies show that nearly 10 percent of night-shift workers have severe reactions to that schedule. Some become overwhelmingly sleepy during the night shift, when they need to be alert. Some have trouble concentrating and focusing on a task. Others can’t really fall deeply asleep during the day, when they need to get some sleep.
There are even studies indicating that night-shift workers have higher rates of developing obesity and Type 2 diabetes. People who aren’t night-shift workers, but who still sleep fewer than six hours per night, also have an increased risk for diabetes. So the risk of diabetes in night-shift workers may simply come from not getting enough deep, restorative sleep.
Studies that find associations between night-shift work and a disease like diabetes don’t prove that the night-shift work causes the diabetes. So colleagues of mine at Harvard Medical School tested that possibility directly. They built an underground living space and asked 21 people to live in it for six weeks. They were shut off from the outside world, with no clue as to when it was night or day. The scientists decided when it was bedtime, and the lights went off. They also decided on the timing and content of meals, and on how active the subjects in the study could be.
For the first three weeks, the scientists made nighttime in the underground space occur at the same time as night in the real world above. Then, they gradually made “night” shorter, and made it occur when it was really daytime in the world above. Finally, they gradually made “night” longer, until it occurred when it was really night in the world above. During that middle period, when study participants slept less and had disrupted circadian rhythms, they developed higher blood sugar levels and started to gain weight.
Another health risk faced by night-shift workers is from driving home after work. Several studies show that they are more likely to have accidents. That’s particularly true if their drive home lasts longer than 30 minutes, which is true of about a third of shift workers. Other studies find that about 20 percent of fatal auto accidents involve a drowsy driver.
To see if night-shift workers driving home were really “impaired” drivers, my colleagues did another experiment. They asked 16 night-shift workers to drive automobiles on a special test track. The workers wore a cap of electrodes that measured their brain waves, which can detect when someone is drowsy or actually falling asleep. Each worker was tested twice: after seven hours of quality sleep and after a night shift.
After the night shift, brain waves revealed the workers were much sleepier. Near-crashes occurred in 38 percent of the workers after the night shift — and in none of them after a good night’s sleep.
In tomorrow’s column, I’ll discuss what shift workers can do to function better and protect themselves.