Recently, there has been no shortage of news about circadian rhythms and sleep. Clearly, interest is growing in this topic - last Sunday's New York Times article entitled 'Yes, Your Sleep Schedule Is Making You Sick' was one of the most emailed articles for the week. Before I dive into the latest research – which holds hope for Delayed Sleep Phase Syndrome sufferers – a quick primer on circadian rhythms is in order.
A circadian rhythm is any bodily process that displays an endogenous (meaning ‘built-in’) oscillation of approximately 24 hours. Influencing nearly all aspects of physical and behavioral changes, circadian rhythms govern everything from appetite to mood to sleep. Circadian rhythms are driven by our 'circadian clock' (also referred to as the 'biological clock.')
The circadian clock is a molecular machine that exists in almost every cell in the body. Consisting of a number of proteins that come together and fall apart rhythmically, the circadian clock controls the transcription of genes and the making of proteins in a 24-hour pattern. Mutations in various clock genes alter the circadian clock and have been implicated in causing chronic sleep disorders like Delayed Sleep Phase Syndrome.
Environmental cues also affect the circadian clock. Light and darkness (both from the Earth's rotation and from artificial lighting) are transmitted into the Suprachiasmatic Nucleus (SCN). Located near the optic nerve in the hypothalamus, the SCN is a group of nerve cells that serves as a 'master clock' - coordinating all the clocks so they are in sync.
Recent research finds that the circadian clock might be influenced by lunar phases. In overnight sleep studies conducted in light-controlled rooms, sleep was affected negatively by the full moon (both later sleep onset and shorter sleep were recorded).
Physiological circadian rhythms such as body temperature, melatonin production and cortisol secretion are key factors for falling asleep. Therefore, the timing of our sleep is based on our circadian rhythms, which are driven by our circadian clock, which are influenced by both internal (genes) and external (environmental) factors. Although this is a burgeoning field, researching are noting that for night owls, sleep times are governed by their biological rhythms, which are NOT modifiable.