General Health

Hampered sleep-wake cycle is associated with mental health issues: Study

A study states that people who are early risers are more protected from mental health disorders than those who are evening owls. 

The Circadian Rhythm aka the body’s biological clock is a physiological process that is essential to regulate the sleep-wake cycle, hormonal secretion, mealtime, digestion, body temperature and other essential activities. The duration of the Circadian Rhythm is around 24 hours and periodical. This internal clock determines how we respond to light and dark exposure and is found in the suprachiasmatic nucleus (SCN) in the hypothalamus of the brain. 

The light activates the SCN through the retino-hypothalamic route. When exposed to light, the SCN signals the hypothalamus to secrete activating hormones like cortisol and increases the body temperature thus enabling sustained alertness and activity. During dark exposure, the SCN signals the pineal gland to produce the melatonin hormone which encourages the body to sleep and rest. Sleepiness is further promoted by the dip in body temperature during the darker hours. 

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Disrupting the sleep-wake cycle can mess up the circadian rhythm. Exposure to blue light during the dark hours from various screens can give the effect of light exposure to the SCN, which can disrupt sleep. Since the circadian rhythm is involved in regulating the body temperature and other homeostatic functions, any kind of hampering can give rise to a host of physical and mental health disorders. 

Cortisol is a stress hormone that contributes to alertness as well as anxiety. Continuous release of the cortisol hormone causes chronic anxiety and weight gain which in turn fuels more cortisol production hence creating a vicious cycle. Desynchronized circadian rhythm correlates with psychological illnesses such as schizophrenia, depression, bipolar disorder, mania, and anxiety. In addition, health conditions such as sleep disorders, obesity, diabetes, cardiovascular disease, and seasonal affective disorder are observed with irregular circadian rhythms. 

A research team from the University of Exeter and Massachusetts General Hospital had previously mapped 351 genes that determine diurnal preference and hence explains the differences in circadian rhythms among different individuals. These genes need to be studied in more detail and the initial results of the study were published in Nature Communications. Another research team from the University of Exeter further went on to investigate the prevalence of various mental health disorders in individuals with disrupted sleep-wake cycles using Mendelian Randomisation methods. The results of these studies were published in Molecular Psychiatry

The team used a statistical method called Mendelian Randomisation to examine whether these genes were causally associated with seven mental health and wellbeing outcomes using data from 450,000 UK adults from UK Biobank’s biomedical database and research resource. Along with the genetic information, participants completed a questionnaire on whether they were a morning person or an evening person. They also measured a “social jetlag” (the differences in sleep pattern between work and free days) in around 85,000 UK Biobank participants whose sleep data was available through actigraphy or wrist-worn activity monitors. 

The team found that people with a diurnal preference of waking up earlier were protected from several mental health disorders. The studies revealed that morning risers are less likely to have depression and anxiety as compared to evening owls. The general well-being of the evening owls was also lower than the morning risers due to circadian misalignment. They also suggested that higher depressive symptoms were seen in shift workers compared to non-shift workers. The team even found out that people who were more misaligned from their natural body clock were more likely to experience social jetlag. 

This study concludes that early-type risers or morning people have lower levels of depression and improved general well being due to lower circadian misalignment. However, further work is required to establish the relationship between genetic diurnal preference and mental health issues mediated through circadian misalignment. If the relationship is determined, mental health and wellbeing in evening people can be improved by introducing further flexibility to the working day. 

Author: Parvathi Nair

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