Not getting a good night’s sleep can do more harm than simply making you yawn during morning meetings. More and more research shows that a lack of sleep can lead to a number of potentially hazardous endocrine disorders.
In February, the Centers for Disease Control (CDC) released a study that concluded that more than one-third of Americans (83.6 million U.S. adults) don’t get the recommended seven hours of sleep in a 24-hour period. A staggering number, but not all that surprising, given today’s ultra-fast, plugged-in society.
It’s also no coincidence that the CDC’s recently reported numbers on the lack of sleep correlate with the ever-rising numbers of obesity and diabetes. More than 29 million Americans have diabetes, and 35.1% of American adults are obese, according to the Endocrine Society’s Endocrine Facts and Figures report. And there are many culprits on which to pin these parallel phenomena – odd work/life schedules, the light from the mobile phone on the bedside table, or simply a lack of understanding of the importance of sleep.
“I think that we as a modern 24/7 society undervalue sleep,” says Peter Liu, MD, PhD, of Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, Calif., “because we don’t really understand how important sleep really is for our overall well-being. We all know, for example, that if you don’t get enough sleep, that you might be grumpy, it might affect your mood, maybe you make a few more mistakes. But we don’t realize that not getting enough actually harms your metabolic health.”
And although there is a lot of longitudinal and epidemiological data linking reduced sleep to the future development of both obesity and diabetes (as well as a host of other adverse health effects, from high blood pressure to frequent mental distress), looking at just how sleep affects the endocrine system is a relatively new field of study. Researchers are looking more and more beyond the usual suspects behind obesity and diabetes – sedentary lifestyle and poor diet – to sleep quality, and even how external and environmental factors affect sleep quality.
The CDC’s report also concluded that clinicians should engage in discussions of sleep health with their patients, so here we’ll take a look at some of the work being done in this realm, as well as some recommendations for better sleep that hopefully lead to better metabolic health outcomes.
Social Jetlag
Researchers who study sleep’s effects on the endocrine system also examine people’s circadian rhythms, mainly what disrupts these natural oscillations between bedtime and peak alertness. Each person has a preferred wake-sleep time, and recognize specific times of day that they feel more alert to do work. This subjective preference is known as a person’s chronotype (e.g., morning people vs. night owls) and is thought to represent individual differences in circadian rhythms.
“We all know, for example, that if you don’t get enough sleep, that you might be grumpy, it might affect your mood, maybe you make a few more mistakes. But we don’t realize that not getting enough actually harms your metabolic health.” – Peter Liu, MD, PhD, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, Calif.
According to a study published in The Journal of Clinical Endocrinology & Metabolism, “Evening types are also more likely to be depressed, overweight, diabetic, and hypertensive, in comparison to morning types.” The study, led by Patricia Wong, MS, of the University of Pittsburgh, looks at “social jetlag” — habitual discrepancies between their endogenous circadian rhythm and actual sleep times imposed by social obligations – and its effects on metabolic health.
“I was intrigued by the amount of literature showing that night and shift workers are at an increased risk for diabetes and cardiovascular disease,” Wong says. “Recently, there have been accumulating findings that when you disrupt people’s circadian rhythms acutely there are physiological changes that, if prolonged, could contribute to disease.”
She says that a 2012 study by Ronneberg et al. linking a self-reported measure of social jetlag to BMI in a large population influenced her interest in expanding the literature and to ask: Does habitual social jetlag, experienced in the community by daytime working adults, associate with cardiometabolic factors?
Wong and her team found that social jetlag does indeed associate with cardiometabolic factors; participants in the study who had the biggest discrepancies between their workday sleep schedules and their free-day sleep schedules had poorer cholesterol profiles, higher fasting insulin levels, larger waist circumference, higher body-mass index, and were more resistant to insulin than those who had less social jetlag.
Even controlling for unhealthy habits like alcohol consumption and smoking didn’t change what they observed in social jetlag. “We included these measures to try and control for other health behaviors that we know increase disease risk. We wanted to keep in mind the possibility that someone who experiences a lot of social jetlag might also engage in different or worse health behaviors,” Wong says. “What we find is that after statistically controlling for individual differences in these behaviors, social jetlag still associates with the outcomes and so we interpret this to mean that there is a specific effect of social jetlag on our health that is not explained by other known risk factors.”
Night Light
And it’s not just societal pressures that could be disrupting circadian rhythms; it could be a product of modern society itself, a rather ubiquitous and seemingly innocuous one: artificial light. Laura K. Fonken, PhD, of the University of Colorado, and her team published research in Endocrine Reviews that examined nighttime exposure to artificial light – the blue glow of the TV in bedrooms at night, streetlights peeking through windows – and how it disrupts circadian rhythms, which, again, has been implicated in contributing to the rise in obesity and diabetes rates.
“We originally came across this phenomenon serendipitously,” Fonken says. “We were actually investigating how lighting environment can affect mood-related behaviors and noticed that the mice exposed to light at night were gaining more weight.” She says they looked back at previous research and noted the substantial evidence that both sleep and circadian disruption are associated with metabolic disturbances, and therefore decided to pursue the correlation of increased exposure to light and night and rising numbers of obesity and metabolic disorders.
It turns out that exposure to artificial light at night creates a kind of domino effect: light reduces sleep quality which throws off circadian regulation which throws off metabolic regulation. “What we try to highlight in the article is the reciprocal relationship between sleep loss, circadian disruption, and endocrine disturbances,” Fonken says. “Light at night has the potential to affect all of these processes and these factors can in turn lead to weight gain.”
“Catch-Up” Sleep
Most of the previous studies in this field look at what happens when you disrupt a normal sleeper’s circadian rhythm in a laboratory. But what about people whose circadian rhythms and sleep patterns are chronically erratic? Liu says that before his study that examined the effects of “catch-up sleep” on the weekends – published in Clinical Endocrinology – researchers recruited normal, healthy individuals who self-reported getting enough sleep and having normal bed times.
“What we did for the first time was we purposefully recruited individuals who self-reported not getting enough sleep,” Liu says. “They reported they didn’t get enough sleep Monday to Friday, and then on the weekend they caught up on their sleep. And the idea for the study came to me, because I am unfortunately one of these people.”
Liu says he and his team wanted to examine the effects of extended sleep and how it would affect insulin resistance, since past studies had shown that when a healthy individual’s sleep is restricted, his or her insulin sensitivity declines. They found that the participants who don’t get enough sleep during the week were able to improve their insulin sensitivity when they caught up on their sleep over three nights (simulating a weekend).
What’s more, the participants were able to sleep 10 hours each night in the laboratory, something they were unable to do over weekends at home, which made the authors note the possibility that their habitual attempts at ‘catch-up’ sleep were suboptimal. “So that means that every one of us, even though we might get nine hours, maybe we need that extra hour, or an extra couple of hours,” Liu says.
Wake Up Call
When NBC Nightly News reported on the CDC’s study and its conclusion that we need to find ways to get better sleep, anchor Lester Holt editorialized, “That may be easier said than done.” Researchers who study sleep’s effects on the endocrine system have ideas and recommendations for getting better sleep, but they warn that more research needs to be done before they can offer definitive answers.
Wong, for instance, is careful to say that correlation does not equal causation, and that she and her team can’t say for certain “what is causing what.” Other studies have suggested eating at later times could contribute to weight gain, and thus individuals with social jetlag could presumably be eating at later times and that this itself could contribute to some of the findings they observed. “We did not have data on what times people ate,” she says, “and so that is why we could not consider this possibility in our analyses.”
She says that one way to potentially test for whether social jetlag is causing the health effects is to conduct longitudinal analyses and see, if over time, social jetlag predicts more risk for the onset of diabetes or cardiovascular disease. Another method is to experimentally test whether inducing social jetlag in people will change their physiological measures compared to when they don’t have social jetlag.
“I think that if more studies come out and replicate what we find,” Wong says, “we should start considering whether individuals can be protected from disease risk if they were able to work/sleep at times more ideally fit with their underlying biological rhythm.”
Sweet Dreams
In their review, Fonken and her team point to a number of ways to prevent exposure to excessive nighttime light, such as blackout curtains or simply removing televisions and computers from bedrooms. They note that solutions are more difficult for shift workers and their employers, but they also note that there is ongoing research into blocking the blue light of the spectrum (to which our eyes are most sensitive) with specially designed goggles and light fixtures.
“That is a major issue with developing a solution for people adversely affected by nighttime light exposure,” Fonken says. “Overall, electrical lighting has benefited society in many ways; we don’t mean to give the impression that we think nighttime light exposure is all bad. Trying to avoid the negative consequences of light at night can be challenging because the negatives need to be balanced with the positive effects of using electric lights.”
She goes on to say that public interest in circadian disruption seems to be growing. People are using the app f.lux – which adapts your computer screen to the time of day – as well as lamps designed to limit circadian desynchrony. “Coming up with better lighting designs for facilities with a lot of shift workers could be a potential strategy to improve some of the negative effects of nighttime light exposure,” Fonken says.
For Liu, even though his team’s study concluded that catch-up sleep improved insulin sensitivity, that doesn’t mean people shouldn’t try to sleep well every night. “I think a good analogy would be eating well,” Liu says. “As a doctor, I tell people to eat well all the time. I don’t say to them, ‘Look, if you eat well on the weekends, then during weekdays Monday to Friday, you can go and eat whatever junk food you like.’”
“Recently, there have been accumulating findings that when you disrupt people’s circadian rhythms acutely there are physiological changes that, if prolonged, could contribute to disease.” – Patricia Wong, MS, University of Pittsburgh, Pittsburgh, Pa.
He stresses that people should plan to get a good night’s sleep, just as someone would plan to eat a healthy meal or go to the gym that day. For now, Liu and his team are looking at the specific hormonal mechanisms by which sleep restriction causes insulin resistance as well as other metabolic and behavioral abnormalities, since, as he says, this provides the evidential basis to convince the scientific community and convince the lay community that sleep has these adverse effects.
Liu says that they’re also recognizing more and more that one reason people don’t sleep as well as they should is because they can’t disengage from technology. “I don’t know about you,” Liu says, “but the first thing I did this morning when I woke up was I switched on my phone and I checked my email, even before I got out of bed. The last thing I did before I went to bed last night was I was on the computer checking email and doing work. We as a society need to learn how to switch off and disengage from technology.”
— Bagley is the associate editor of Endocrine News. He wrote about the Early Career Forum at ENDO 2016 in the March issue.
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