USNEWS：睡眠和肺癌之间有联系吗－褪黑素真有大作用！

WE ALL KNOW THAT getting a good night’s rest is helpful for overall health and wellness. But that basic rule of thumb may be even more true than we realize when it comes to cancer. Emerging science has begun to suggest that the critical function of sleep may have more to do with whether you develop cancer, particularly lung cancer, and how quickly it progresses.

Scientists are still unraveling whether and how sleep and the development and progression of various kinds of cancer are linked, but there is some evidence indicating that there’s a connection between lung cancer and sleep related to two other conditions: disruption of circadian rhythm and obstructive sleep apnea.

The National Sleep Foundation defines circadian rhythm as “basically a 24-hour internal clock that is running in the background of your brain and cycles between sleepiness and alertness at regular intervals. It’s also known as your sleep/wake cycle.”

Although we still have a lot to learn about how circadian rhythm works, recent studies into the effects of shift work on the body have indicated that working nights may well elevate your risk of certain types of cancer. Although much of this research has focused on breast cancer, there is some indication that disrupting your circadian rhythm could also be associated with a slightly greater risk of developing cancers of the digestive system and the lungs.

Inflammatory immune response may be the mechanism underlying these connections, says Dr. Reena Mehra, director of sleep disorders research at the Cleveland Clinic. “We’re a young field and the research is emerging, but ultimately the goal is to see if we can do something to intervene to mitigate development of cancer, progression of cancer and better treat cancer” by leveraging our understanding of the circadian rhythm and how it’s connected to health. (So-called chronotherapy is a developing field of treatment for a few types of cancer that times the delivery of drugs and other treatments in sync with the circadian rhythm to improve the body’s response.)

With lung cancer in particular, another area of concern is a condition called obstructive sleep apnea. People with this condition actually stop breathing while they’re asleep, which leads to low levels of oxygen in the blood. “The best way to resolve that event is by awakening,” says Dr. David Gozal, professor of pediatrics, neuroscience and neurobiology at The University of Chicago and a pediatric sleep medicine physician at the University of Chicago Medical Center.

Gozal and his team have conducted a few studies in animals looking at the effect of these drops in oxygen in the body – called intermittent hypoxia. A 2016 study published in the journal CHEST found that in mice that had both lung tumors and sleep apnea, “the tumor proliferated faster and was much more aggressive locally,” he says. That model didn’t look at metastatic disease – stage 4 cancer that has spread to other organs – but Gozal says the theory why sleep apnea seemed to worsen the prognosis is that these sleep interruptions lead to a change in “the way the immune system responds to the presence of the tumor.” It appears that waking up often causes “these cells to lose some of their ability to identify and fight or destroy cancer cells.”

Further, Gozal found that “many of the cancer cells, when they’re exposed to intermittent hypoxia, have a tendency to become less well-differentiated. In other words, they become more stem-cell like, which is a bad sign for cancer. The less differentiated these cells are, the more aggressive they are and the more likely they are to proliferate faster and invade other tissues and be very aggressive. When you wake up many times trying to catch your breath, there is clearly an effect on the tumor growth,” he says. Again, it seems that disruption of sleep alters how the immune system works and that “plays against our defenses against cancer, facilitating both the proliferation and the local invasiveness of these tumors.”

Even if you don’t have sleep apnea, simply having lung cancer can impair lung function in some people, which can also lead to disrupted sleep. Mehra says in some patients, a condition called pleural effusion leads to an accumulation of fluid around the lungs that can make breathing freely more difficulty. And patients with endobronchial disease sometimes develop a tumor invading the airway. “There’s so many subtypes of lung cancer and also types of [symptoms] that can sometimes be sleep disruptors.”