medwireNews: A plenary session at the 58th Annual ESPE Meeting in Vienna, Austria, has highlighted how wide-ranging the risks associated with sleep and circadian rhythm disruption are.

Russell Foster, from the University of Oxford in the UK, began the session by explaining that circadian rhythms are generated by the suprachiasmatic nuclei, often known as the master biological clock, which is located in the anterior hypothalamus. This biological clock is present in every cell in the body and is entrained principally by exposure to the light–dark cycle, but also by other local modulators such as food.

“The whole point of this is that the circadian system can fine tune physiologic behaviour to the various demands of the night–day and the sleep–wake cycle”, he said.

Indeed, when and how long we sleep for is largely defined by the biological clock, along with sleep pressure (homeostatic drive) and societal pressures, such as work and family.

Foster reported that between 32% and 36% of our lives are spent sleeping, but it is only in the last 10 to 15 years that researchers have begun to look at what critical processes occur in the sleeping brain. They have discovered that these include developing memories, processing information, emotional processing, rebuilding metabolism, the regulation of tissue growth and repair, replacing energy reserves and the removal of waste products.

He continued that sleep arises from an interaction between all of the key brain neurotransmitter systems and multiple brain structures, indicating that “sleep is a global brain event.”

Foster then discussed the importance of getting light exposure at the correct time – dawn and dusk – for appropriate regulation of the sleep–wake cycle. The amount of light needed for entrainment, however, can be a source of controversy. He said that although people believe that light from computer screens can shift the biological clock when used in the evening, this is not the case, as the amount of light they generate is not intense enough. Rather, it is the duration of use leading to shortened sleep that is the problem.

And Foster stressed that sleep disruption is so much more important than just feeling tired at an inappropriate time. He said that short-term disruption (1–2 nights of sleep loss) is associated with feelings of stress and anxiety, difficulty in waking up or falling asleep, loss of empathy, impulsivity, memory impairment and clumsiness.

Sustained sleep loss can lead to increased stimulant or sedative use, immune suppression, increased risks for infection, cancer, cardiovascular disease and type 2 diabetes, as well as metabolic abnormalities and indigestion.

Both short-term and sustained sleep disruption can affect mental wellness in those vulnerable to mental illness, including increased mood instability, anxiety, paranoia, hallucinations, and exacerbation of symptoms of bipolar disorder and schizophrenia.

Conversely, data have shown that increasing exposure to light during the day (10,000 lx for 30 min/day) can reduce depression to a greater degree than fluoxetine, with symptoms reducing further still when the two are combined.

Foster also told delegates that he is currently investigating a drug that can be used for the pharmacologic replacement of light to treat people with non-24-hour sleep–wake disorders. He said that CT1500 0.2 mg/kg shifts the biological clock to a similar degree to that of natural light and could potentially be used to give back a sense of time to people who have lost their eyes due to trauma.

He concluded that sleep disruption has got to be “taken seriously”.

By Laura Cowen

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