Missing out on one night of shut-eye shouldn’t hurt you. But disrupt the sleep cycle for a longer period of time and your body — and your brain — won’t be able to recover so easily.
That was the central finding in a University of Pennsylvania study that found chronic sleep deprivation — like that experienced by many shift workers — could actually damage neurons in the brain.
The findings indicate that the idea of quickly making up for a “sleep debt” isn’t really accurate, said Sigrid Veasey, associate professor of medicine at the Perelman School of Medicine at University of Pennsylvania in Philadelphia.
“If you were to take one night and do a short-term sleep loss, that’s probably OK — you can probably quickly make that up with a nap. But what (much) of our society is doing is repeatedly short-changing the sleep all across the week, and then hoping to make it up on the weekend. And that’s what we think doesn’t really happen,” she said.
Lasting effects of sleep loss
It’s not so easy to bounce back from repeated interruptions in the sleep cycle because chronic sleep loss can have lasting effects on the brain, said Veasey, who co-authored the study. Previous studies on humans have suggested chronic sleep loss has a lasting impact on attention, she said.
“So we sought to look for the cells in the brain (that) are necessary for maintaining that perfect attention,” said Veasey, adding that these are called the locus coeruleus (LC) neurons.
“Every time you need to be alert and pay attention to something, these are the cells that play a critical role. And what we found was that mice that were subjected to just one week of a shift worker’s schedule of staying awake for eight hours when they normally would be asleep, that was sufficient to cause loss of the cells and injury to the remaining cells.”
This suggests that sleeping in on the weekend isn’t enough to help the brain recover from repeated sleep deprivation.
“The concept is that the brain takes much longer — if it does recover, the recovery process is much longer than we had envisioned,” said Veasey.
“It’s not going to have a major impact on someone’s cognition in general. The little things where it does play a role… (is) in mood. So people would be expected to be less interested in activities, and it may shift someone who’s predisposed to depression over to depression.”
It may also impair a person’s attention span, said Veasey — which has huge safety implications for many shift workers.
Increased injury risk
Workplace injuries account for about 25 per cent of all injuries working-age adults experience in Canada, according to Cameron Mustard, president of the Institute for Work & Health in Toronto.
And the risk of a workplace injury is higher for those who do shift work, he said.
“The (study) we’ve completed recently did find, for both men and women, that working evenings, nights, does carry with it an elevated risk of work injury,” said Mustard.
“Of all the work injuries experienced by women, about 12 per cent are due to the higher risk that is present in working evenings or nights… For men, the proportion is about six per cent.”
While their research has not yet been able to clearly determine why this is the case, two factors around sleep disruption are likely at play — sleepiness and fatigue, he said.
“The sleepiness idea is even if you’re well-rested, if you’re awake at midnight, your body is trying to go to sleep. It’s your circadian rhythm. And there are many things that the body can habituate to… But it’s one of the more vigorous hormones in the human body. Your body really wants to go to sleep when night falls,” said Mustard.
“Related to sleepiness is fatigue. So if you’re not well-rested — which is going to be increasingly a risk if you’re working late into the night — you’re going to be increasingly fatigued.”
However, the risks inherent in shift work are still largely “invisible,” he said — under-researched and not well-understood. That’s a major problem when one-quarter of the country’s population is engaging in some form of shift work.
“About 25 per cent of Canadian workers will do some hours in their work week other than 9-to-5, Monday to Friday. And that’s a big number,” said Mustard.
“So these are police officers, these are nurses, these are truck drivers — it’s quite a wide range of occupations that have within them either the expectation or the possibility that people will be working other than 9-to-5, Monday to Friday.”
Other health concerns
Neuron damage and increased risk of injury are not the only concerns around shift work and chronic sleep disturbance.
Shift work is classified by the International Agency for Research on Cancer (IARC) as a “probable human carcinogen,” said Amy Hall, occupational hygienist at CAREX Canada in Vancouver.
“Shift work was (designated) ‘probable’ because there was quite strong experimental evidence and evidence in animals, but in terms of human studies, there was sort of a limited amount of evidence that indicated that breast cancer was an outcome of a lot of shift work — we’re talking decades,” she said.
“In terms of health effects, there is strong evidence for some things, and there’s other areas where evidence is developing.”
There is fairly strong evidence shift work results in sleep disorders and higher rates of workplace injury.
There’s also developing evidence shift work may be linked with heart disease, mental health, gastrointestinal problems and certain other types of cancer — most notably prostate cancer, said Hall.
But more research is desperately needed.
“The problem is that because there are so many definitions of shift work and it is a new and evolving area, the research, the evidence still needs development,” she said. “(And) we need more research into the types of strategies that are most effective in reducing health effects.”
More research is what Veasey plans to do. While her initial study used mice to study neuron damage, she’s planning to move on to working with humans.
“We’d like to examine post-mortem shift worker brains and then follow shift workers. And then there also will be some in-lab shift worker studies looking at when do patients really recover from their sleep loss — how long does it take?” she asked.
“If you did a week with three or four all-nighters, when does your function really, truly return to normal?”
It’s research that’s even more pressing given the large number of people who are affected.
“This is incredibly pervasive… (it) affects a lot of people,” said Veasey. “It’s that paradox where you feel like you need to skip your sleep to work harder to get that upward edge in life, and you may be actually cutting short that edge if you’re really harming the brain.”
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