by Amy Haddlesey
As students, we are no strangers to staying up late to do schoolwork or the hardships of getting up early for an 8:30 class. A good portion of the population will find one of these activities easier than the other, which means that people can fall into one of two camps: night owls or early birds. The population is said to have a normal distribution when it comes to how we organize our behaviour within the 24-hour day, with most of us in the middle of the two extremes, but there are still individuals that find themselves leaning towards one or the other. The term ‘chronotype’ is used to describe your preference for wakefulness, which is divided into late chronotypes (LCs), intermediate chronotypes (ICs), and early chronotypes (ECs). ECs are characterized by their difficulty with staying up late, and LCs are characterized by their difficulty with getting up early. Chronotype is both age and sex-dependent. Interestingly, a higher percentage of females are ECs.
Chronotype-specificity is dictated by the interplay between neural circadian rhythms and homeostatic oscillators. Both essentially involve regulating the cellular processes involved in telling our bodies when to sleep, wake, and eat. While circadian rhythms, or the “body clock”, can respond to or be affected by external factors (eg. sunlight), the homeostatic oscillators are considered internal, independent regulators. However, it is the interplay between the two that regulates the overall fluctuation between sleep and wakefulness over the course of each day. Recent research into the genetic basis of our inner clocks has revealed that our circadian rhythms are important time reference systems that interact with the environment. Understanding how circadian clock function is most affected could lead to helpful interventions in mediating clock dysfunction improving human health and welfare. In this study, more than 80 different genes were shown to be expressed differently between late and early chronotypes in fruit flies. Furthermore, it wasn’t expression alone that separated the groups; there were also different genetic variations present between late and early chronotypes. Overall, there are many factors at play in determining your preference for how you organize your day that may be beyond your control.
Studies have found that the differences between chronotypes extend beyond sleeping preference. Different chronotypes are also associated with differences in cognitive performance, gene expression, endocrinology, and lifestyle. Most notably, LCs tend to suffer from a conflict between internal and external time (‘social jetlag’) that may cause them to suffer more mental stress. In other words, a night owl’s tendency to sleep through the day and stay up late comes into conflict with the typical hours of the social day, which may cause LCs to experience jet lag-like symptoms as they try to adjust. Similarly, LCs may have to adjust to working hours or school hours as well. One paper suggested that with an increased understanding of chronotype-specificity, work schedules could ideally be designed to fit your wake/sleep schedule. It is important to note, however, that most workplaces have to fit into regular business hours, and so it’s unclear how many workplaces could be suited to this “customizable” workday and how large of a range can be accommodated. With that said, there are some businesses that set formalized flex hours, where there are certain hours you must be in the office, but you can shift the surrounding hours to your own preference (come in late so you leave later versus coming in early so you leave earlier).
As much as we try, we can’t always control our schedule and that means we are sometimes forced to conform to a routine at odds with our chronotype. A recent study involving adolescents has shown evidence linking chronotype and academic performance. During adolescence, our chronotypes are typically at our latest, as might be expected with the typical tendency of teenagers to stay up later and sleep in later when compared to other age groups. As discussed, a late chronotype can mean a mismatch between our circadian clock and the early school clock. As a result, it was found that late chronotypes generally have lower grades. This finding is especially interesting when there isn’t an agreed upon relationship between early and late chronotypes and IQ. Instead of a difference in IQ, these lower test grades could be due to the circumstantial or ‘social jet lag’ discussed earlier causing sleep deprivation in LCs. The effect of chronotypes seem to be strongest in the morning and disappear in the afternoon, which is in line with views that LCs struggle to adjust to an earlier schedule.
So what can we do with this information? There are many strategies recommended to improve sleep quality including a consistent sleep schedule or reducing your exposure to blue light before bed. However, it may be that these findings indicate a need for schedules better suited to our natural bodily rhythms that could lead to positive outcomes for public health and productivity. It’s hard to imagine what tangible programs or policies could be established with this information, but it’s an interesting subject that may be worth our attention.