Circadian-Type: Are you a Morning- or Evening-type?

 

Many physiological processes (e.g., regulation of body temperature) follow a 24-hour cycle or circadian rhythm.  These circadian rhythms are controlled by our biological clock, which is centralized in the suprachiasmatic nucleus (SCN) center of the brain. Light is an important zeitgeber that entrains (synchronizes) our circadian rhythms. When light enters the eye, it sends signals to the SCN, which, in turn, regulates a number of different processes that ultimately influence our sleep-wake timing. One of these processes is the secretion of the hormone, melatonin. In general, light exposure reduces melatonin – thus levels are very low throughout the day and increase throughout the night. There are, however, individual differences in the extent to which the diurnal rhythm of melatonin is slightly advanced or delayed. These differences in the pattern of melatonin secretion (along with differences in body temperature), are underlying factors that determine one’s circadian-type.

On the one hand, morning-types (“larks”) have a preference for earlier sleep-wake patterns, whereas evening-types (“owls”) opt for later sleep-wake patterns. Morning-types perceive the mornings as the most optimal time of day for peak performance on physical and cognitive tasks, relative to evening-types (who prefer later in the day). A number of studies have shown that morning- and evening-types differ on a number of different psychosocial outcomes, including: academic performance, alcohol/drug use, personality, and emotional adjustment.

In the proposed study, we hypothesize that circadian-type may moderate the impact of the timing of exercise on sleep outcomes. To measure circadian-type, we propose both an objective and a subjective approach. Objectively, we will index circadian-type by assessing individuals’ diurnal patterns of melatonin secretion across the day for 7 days (via saliva samples). Subjectively, participants will complete the validated Morningness-Eveningness questionnaire (MEQ). This is a 19-item survey that measures perceived preference for daily activities.

If you are celebrating Thanksgiving and/or have the day off, make a mental note of your sleep-wake patterns on days when you don’t have school/work/social commitments. This will give you some insight into your preferred/true circadian-timing, which, unfortunately, is often at odds with our social clocks.

Wanna know whether you’re a morning-type or an evening-type? Or maybe you’re in the middle of these two extremes (i.e., a neither-type)? –

Take the MEQ survey here!

Happy Thanksgiving!