As much as we may understand that quality sleep habits are important to our overall health, the reality is that, for many people, getting a solid eight hours at the same time every night just isn't possible. Whether your sleep habits are thrown off by a baby that won't sleep, a job that requires you to work night shifts, or just straight up insomnia, there are lots of us who are stuck feeling chronically groggy. But while lack of sleep in itself can cause health issues, a recent study has found that your circadian rhythms could affect your breast cancer risk, according to Science Daily, meaning that women with unconventional work schedules, or those who travel often and experience jet lag, may be more likely than others to develop the disease.
Scientists are constantly investigating ways to better treat or prevent cancer, and one of the things they've discovered is that disruptions in circadian rhythms — aka our bodies' "internal clocks" — can increase the risk of cancer. And now, thanks to researchers at Texas A&M University, we may know a little bit more about why that might be occurring, at least in cases of breast cancer. In the study, published in the scientific journal Development, researchers found that the same part of the brain that controls sleep patterns also controls related "peripheral clocks" in our bodies. Within each cell's peripheral clock is a regulatory mechanism called Period 2 (aka Per2), that also plays "a crucial function" in the development of mammary glands in mammals, and which appears to have a protective effect against breast cancer in mice. When circadian rhythms are disrupted though, that process can be interfered with, putting women at higher risk of tumor development.
The scientific community has certainly come a long way overall when it comes to understanding breast cancer — although it's the most common type of cancer in women, survival rates can now be as high as 99 percent if it's caught early and hasn't spread, according to New Scientist. Yet over the years, researchers have found that shift workers are more prone to breast cancer than those who work regular daytime hours, and in 2007, the World Health Organization designated shift work as being "probably carcinogenic to humans,” according to Reuters. One theory is that disruptions in circadian rhythms affect melatonin production, which Reuters noted can "[act] as an antioxidant protecting DNA from the type of damage that leads to cancer." But in recent years, the affect of circadian rhythm disruption on Per2 specifically has also emerged as a significant factor.
In 2016, a study conducted by researchers at MIT's Koch Institute for Integrative Cancer Research found that when normal light/dark cycles are disrupted — such as when people work night shifts, or when they are jet lagged — the levels of the protein encoded by Per2 stop fluctuating as they are supposed to, which may allow lung tumors to grow faster and more aggressively. Now, the Texas A&M research suggests that a similar process can occur with breast cancer, too.
While the findings still don't necessarily prove that the shift work makes women more susceptible to breast cancer specifically because of decreased Per2 expression, lead researcher Weston Porter told Science Daily that his team's next step is to "[investigate] how [their] findings relate to humans," as that they believe "there is a direct relationship," between Per2 and breast cancer development. And Porter's findings certainly seem extremely valuable for shedding some light on why it is that circadian rhythm disruption may be putting women at risk.
Earlier this year, researchers in China analyzed 61 studies to examine the link between night shift work and cancer, according to The Independent, and found that women who work night shifts "are 20 per cent more likely to develop some form of cancer," and that "every five years spent doing regular night shift work" can increase a woman's cancer risk by about 3.3. percent, which means that the sooner the cause can be identified, the better.
Although the lack of definitive answers is scary (especially for those who work as nurses, firefighters, or other jobs in which night shifts are essential), for now, there are at least some options for mitigating preventable sleep disruptions until researchers can provide better answers. For one, it's likely a good idea to limit exposure to blue light at nighttime, according to The Telegraph, which can keep you awake unnecessarily (in other words, turn off your phone or tablet), and aim to limit lifestyle behaviors that have also been linked to a higher cancer risk, like drinking, smoking, and poor eating habits. And if you do work regular daytime hours? It's probably a really good idea to make getting full night's sleep a priority whenever possible.