Here is some health advice for you and everyone else in the world: go to sleep. Over the past decade, scientists have linked sleep deficiency with increased risk of heart disease, obesity, diabetes, and mood disorders, among other things. Unfortunately, how much you sleep is not the only factor when it comes to good sleep hygiene. Three new studies published within the last month suggest that when you sleep, and how consistent your sleep schedule is, also affect risk for diseases like diabetes and cancer.
The human body operates on a circadian rhythm — the hardwired 24-hour cycle that dictates when we sleep, wake, and eat. The tempo of circadian rhythm varies between people (you really can be a morning person or a night person), but there is a natural cycle for everyone. Rapid changes in living and working conditions, however, have led to a disconnect between how people live and how their bodies naturally operate. For example, you may feel best going to sleep at 1 a.m. and waking up at 9 a.m. But if you work a job that requires you to be on the clock at 7 a.m., you will either have to forfeit sleep or disrupt your circadian rhythm.
A study published in The BMJ on November 21 shows that these kinds of disruptions can have large effects on long-term health. Analyzing data on almost 150,000 U.S. nurses from two different longitudinal studies, the researchers found that working three night shifts per month increases the risk of developing type 2 diabetes by 30 percent for every five years worked. People with other risk factors, like smoking and a lack of physical activity, were almost three times more likely to develop type 2 diabetes than nurses who didn’t have additional risk factors and work rotating night shifts. “These findings suggest that most cases of type 2 diabetes could be prevented by adhering to a healthy lifestyle,” the study says. “The benefits could be greater in rotating night shift workers.”
On November 30, a review published in Advances in Nutrition examined the relationship between chronotype — whether you are a night or a morning person — and overall health. While the researchers’ conclusion was modest (“further research is required”), they note that chronotype may be an important factor when it comes to diet. “Overall, cross-sectional studies suggest that evening chronotype is associated with lower intake of fruits and vegetables and higher intake of energy drinks, alcoholic, sugary, and caffeinated beverages, as well as higher energy intake from fat,” they write. These kinds of eating habits can increase glucose levels before going to bed, which could lead to higher risk for type 2 diabetes. While the authors say that more research is needed to establish a link between chronotype and risk, the dietary habits of people with an evening chronotype in conjunction with the circadian disruption of working a night shift shows that these risk factors stack on one another.
On Monday, researchers from the University of Southern California’s Michelson Center for Converging Biosciences published a study in PNAS detailing one mechanism that could account for this relationship between circadian rhythms and risk of disease. They found that the activation of HNF4A, a protein in liver cells that “plays essential roles in the development and physiology of liver, pancreas, kidney, and intestines,” is closely tied to the body’s circadian rhythm. When the circadian rhythm is disrupted, HNF4A doesn’t function properly, which can lead to liver cancer and MODY1, a rare form of diabetes. “Humans are not evolved for night shifts, nighttime lights and intercontinental travel,” author Steve Kay told USC News. “Modern-life challenges to our circadian system present a long-term threat to our health.”
Together, these studies demonstrate that a society that structures life around economic interests rather than our innate rhythms can have unforeseen health effects. Of course, some of this is unavoidable – there will always be medical professionals working at all hours, and many people are forced to work night shifts to make enough money to survive. But with the rise of gig economy jobs like driving Uber or delivering food, more people are becoming shift workers with irregular hours. Amazon products don’t magically appear when you pay for one day shipping; someone has to fulfill that order overnight. Outside of healthcare, places where many people work the night shift – like a 24 hour fast food restaurant — are typically less well paid, too, leading to a confluence of factors that tugs you towards poor health.
The price of convenience might be more than a delivery fee; it could come at the expense of public health, too.