How Does Sleep Influence Cancer Risk?

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IS THERE ANY BETTER feeling than waking up refreshed and rested after a really good night’s sleep? That sensation might be an indication of how good high-quality sleep is for you, not just for meeting the challenge of the day ahead, but for your longer-term health and wellness. A growing body of research into the connection between sleep and chronic diseases has noted that there could be an association between shut-eye and your chances of being diagnosed with an illness such as diabetes or cancer later on.

It seems intuitive that there might be a connection between sleep and cancer risk. After all, cancer is an overgrowth of cells that should otherwise have been regulated or repaired before they got out of control. Much of the body’s work to regulate this cellular growth occurs during sleep. “So many things are happening while we’re asleep,” says Amanda Phipps, an epidemiologist and researcher at Fred Hutchinson Cancer Researcher Center in Seattle. “It’s a time when we most efficiently repair DNA damage. The body is also doing things like controlling the growth of cells, turning on certain genes and switching off others and promoting the immune system. Sleep is a time for repair and restoration of our bodies, but it’s more than just that. It’s also building up our immune systems so we can better protect ourselves during the day.”

If that period of time when the body is busy rebooting and fortifying its defenses is chronically shortened or disrupted, it stands to reason that could eventually have serious repercussions for cancer risk down the road.

From a biological perspective, there are a lot of good reasons for us to suspect that insufficient sleep, chronic sleep debt or short sleep duration could have an impact on the development of cancer,” Phipps says. “We know in particular that when people don’t get enough sleep, when they’re chronically sleep-deprived, we see that can lead to chronic inflammation and insulin resistance.” Chronic inflammation has been associated with several kinds of cancer, and insulin resistance is a precursor to diabetes that occurs when your cells don’t respond appropriately to the insulin the pancreas makes to help your cells take up glucose from your blood. Inflammation and insulin resistance can both “set the stage for cancer by contributing to DNA damage,” Phipps says.

In addition, “inadequate sleep also results in suppressed levels of melatonin,” a hormone that promotes sleep but also “can play a role in protecting against DNA damage and acts as a tumor suppressor. When we’re not getting enough sleep, all these things can happen, which in theory could really set the stage for promoting the development of cancer,” she says.

A few studies over the years have supported the notion that lack of sleep and poor sleep quality could be connected to cancer risk, particularly for lung and colorectal cancers. A 2017 study in the journal Environmental Health Perspectives noted an increased risk of breast cancer among participants who had higher exposures to nighttime light. These findings support the notion that disrupted circadian rhythms are part of the equation.

Circadian rhythm is the “24-hour cycle of night and day or sleep and wake,” Phipps explains. “So many of our physiological functions hinge on that and they’re synced to that cycle. When we’re not getting enough sleep or we’re getting disrupted sleep and waking up in the middle of the night because of light or noise pollution, a screaming toddler or needing to use the bathroom or sleep apnea, all that really has a bearing on our ability to sustain a healthy circadian rhythm. And when our circadian rhythms get disrupted, all the physiological functions that are tied to that rhythm can also get disrupted, including control of cell growth, repair of DNA damage and gene expression. It’s not just about sleep duration, it’s also about healthy sleep patterns and good quality sleep that’s consistent in its timing.”

Although the connection between sleep and cancer risk might seem logical, zeroing in on exactly how the two are connected is challenging, says Dr. Kala Visvanathan, professor of oncology and epidemiology at the Johns Hopkins Kimmel Comprehensive Cancer Center in Baltimore. As a cancer epidemiologist and medical oncologist, Visvanathan says it’s a complicated affair to accurately measure sleep, sleep duration and sleep quality in human study participants with regard to how each translates into cancer risk and mortality later on. She says studies looking at sleep and how it relates to cancer can measure sleep in different ways – either retrospectively reporting sleep quantity and quality from years ago or asking for a snapshot of current sleep duration and quality and then trying to follow up later to see how many people developed cancer. Most studies rely on participants to self-report, which has some limitations, Visvanathan says. “If you really want to understand if sleep is associated with subsequent cancer, you need to have measured sleep before the cancer starts. That’s challenging because it would mean you’d have to have already collected these measurements in the ’60s, ’70s or ’80s,” Visvanathan says.

Still, she says “there is some benefit to self-reporting over time because you get an average idea. But the questionnaires are limited in what they can assess. For example if someone asked me, ‘How well are you sleeping?’ that might be difficult to determine.” However, she notes these sorts of questions are good at pinpointing people who are at the extreme ends of the spectrum. But to figure out exactly how sleep influences cancer risk and mortality will require finer data gathering and analysis of all those people in the middle.

So the answer about whether and how much sleep influences cancer risk isn’t complete at the moment, but Visvanathan says she thinks our current fitness technologies are going to add a lot of finer detail to our understanding of sleep and cancer risk in the near future. “In the world of Fitbits and novel technologies that measure things like heart rate and sleep, this is a great opportunity to get an even more detailed measurement of sleep.” The rise of artificial intelligence, machine learning and more sophisticated data analysis techniques will likely eventually help us leverage the vast amounts of data our health monitors are generating to fill in some of the missing details regarding the question of sleep and cancer. “It’s an exciting time to really start to understand this at a finer level,” she says.

In the meantime, we do know that adequate sleep is important to health for a range of reasons, not just cancer risk. If you’re struggling with insomnia, sleep apnea (a condition that causes people to stop breathing momentarily during sleep and wakes them up many times per night) or other forms of disrupted sleep, you may want to consider seeing a sleep doctor for evaluation and treatment. This specialist can help you determine whether you have sleep apnea or another condition that’s disrupting your sleep and possibly putting you at higher risk of other illnesses. You should also establish a set routine for sleep and wake times and a pre-bed ritual. It’s nice to sleep late on the weekend, but if you’re relying on that to make up for a sleepless week, “it doesn’t undo all the damage we may have done by depriving ourselves of sleep five days a week,” Phipps says.

Other sleep hygiene tips include making the room darker, quieter or a little cooler and getting plenty of physical exercise during the day, which also helps promote sound sleep. “More than anything, it’s a matter of trying to make sleep a priority,” Phipps says, noting that it’s important to recognize “that good sleep is important not just for long-term outcomes like cancer or cardiovascular disease, obesity or diabetes – we know that good sleep has an impact on all of those things. But also just in the short term I think we’re all familiar with how much better we feel after a good night’s sleep or how much worse we feel after getting poor sleep.” Whether you’re worried about your risk of developing cancer or not, Phipps says good sleep is “fundamental to so many things.”

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