Chronobiology: Stepping out of time - Eisenstein - 2013 - Article

According to Elizabeth Klerman, who studies human circadian rhythms, desynchronisation of the natural circadian rhythm can cause chronic sleep problems. Researchers are now attempting to understand the severity and prevalence of this problem and developing strategies to reset the biological clock.

Derk-Jan Dijk, director of the Sleep Research Centre in Guildford, argues that the entire body is a clock. Different body tissues have their own cyclic rhythm that is governed by genetic processes. Although these rhythms vary from tissue to tissue, they are tuned to one regular rhythm. This rhythm appears to be derived from the suprachiasmatic nucleus (SCN). The SCN receives signals from melanopsin receptors in the eye, which are activated by light. In reaction to these signals, the SCN sends hormonal signals tot he rest of the body. Exposure to light is therefore crucial fort he natural biological rhythm.

However, other factors can affect the circadian rhythm as well. Some blind individuals, who do not have melanopsin receptors, do show a circadian rhythm in response to other external signals. Other blind people, however, have difficulty employing a regular rhythm.

Furthermore, although the circadian rhythm is largely governed by light, considerable differences exist between individuals. Some people are typical early birds, whereas others can be characterised as evening owls. Researchers have not yet identified a proper technique to measure the individual internal clock. Melatonin levels can be measured as an indication for the biological night. However, regular measurements are needed for this technique to be reliable, which poses difficulties in large-scale population studies. Therefore, the most widely employed method is the self-report instrument.

Based on such a large-scale study, researchers from Munich demonstrated that the rhythm changes drastically over the lifespan. Moreover, the study provided insight into artificially altered rhythms in modern daily life. Most people work inside and use artificial light; they exhibit much bigger differences in their rhythm than people in rural areas who work outside and are exposed to natural light.

People who work in night shifts or experience large shifts in their rhythm for other reasons can experience problem on the long term. Furthermore, many people suffer from a ‘social jetlag’, when their weekend rhythm differs significantly from their week work rhythm. These shifts do not only cause fatigue on the short term, but are also associated with cardiovascular disease, obesity and other health issues.

Blue light is the most important factor in disturbing the circadian rhythm. The SCN is most sensitive to this type of light. Red light, on the other hand, hardly has an effect on the melanopsin receptors. Therefore, adapting artificial light use to the most suitable light for the time of the day could improve the maintenance of a healthy circadian rhythm.

This has been studied in astronauts in the International Space Station. Regulation of blue light helped to maintain a regular sleep-wake rhythm. This finding suggests that regulation of blue light in office could be a solution to large-scale sleep problems. However, the effect of implementing blue light accomodations in large groups has not yet been studies. Possibly, an individualized approach with a combination of melatonin medication and light adaptations is most effective for people who are exposed to large shifts in their natural rhythm.

Researchers argue that we need a better understanding of natural sleeping patterns in order to help people sleep better and at the same time be productive an happy. To achieve this, large-scale studies are essential.