The toll of the body clock
Story Clarisa Collis
It’s often said that life is too short, yet it’s the longest experience we’ll ever know.
Keeping track of every second, including an average of 25 years spent sleeping, are the age-old hands of time that have their axis in the brain.
There, set in a dense cluster of cells in the brain’s hypothalamus, is a master body clock that has evolved to keep time with the 24-hour solar cycle.
Taking cues from changes in light and dark information in the world around us, this master clock is synchronised to the day/night cycle and coordinates time in other peripheral body clocks inside organs throughout the body.
Monash University’s Professor Shantha Rajaratnam says this complex network of internal clocks measures time to regulate the sleep-wake cycle needed to optimise the body’s physiological environment and, ultimately, its health and functionality.
Our master body clock controls the release of the hormone melatonin at night, promoting night-time sleep in humans.
Interfering with this innate, natural rhythm in modern times, however, is the omnipresent potency of artificial light that’s associated with a constellation of damaging sleep disorders.
Professor Rajaratnam, program leader in the Cooperative Research Centre for Alertness, Safety and Productivity – a consortium comprising 29 organisations spanning universities, research institutes, industry, policy, regulatory agencies and insurers – is focused on one particular sleep disorder.
A sleep and circadian medicine expert, he says delayed sleep phase disorder (DSPD) epitomises the health risk that stems from internal body clock disturbance.
This is because DSPD, characterised by an inability to fall asleep and wake up at socially acceptable times, is linked to a range of unhealthy side effects.
“The abnormally late body clock that delays sleep timing and results in inadequate sleep over time causes significant health impacts,” says Professor Rajaratnam.
Research funded through the National Health and Medical Research Council found that patients with DSPD who have a delayed body clock were four times more likely to have depressive symptoms than patients without a delayed body clock.
This research project led by Professor Rajaratnam further highlighted the importance of an objective diagnostic test for the disorder.
Of 182 people with delayed sleep habits in a randomised controlled trial, 43 per cent of participants diagnosed with the disorder by a clinician did not have abnormal body clock timing relative to their required sleep time.
To overcome the dilemma of inaccurate diagnosis, the trial at three sites – Monash, the University of Sydney and Flinders University – suggests biological testing be used for DSPD.
This test, which shows potential for widespread clinical application, measures concentrations of melatonin in saliva, helping to separate the influence of body clock malfunction from other factors contributing to delayed sleep.
“In a healthy adult, melatonin levels typically start to increase at about 9pm, or about two hours before sleep – whereas in a person with DSPD, the rise in melatonin occurs much later, for example at midnight or later,” says Professor Rajaratnam.
A follow-up Monash study has also shown that administering melatonin is an effective treatment for the disorder.
Now driving the ongoing DSPD research is the finding that there are two distinct phenotypes of the disorder: circadian and non-circadian.
Professor Rajaratnam says possible causes of non-circadian DSPD include insomnia, light exposure, poor sleep habits and psychological or psychiatric conditions, such as anxiety disorders.
Monash University’s Dr Sean Cain is exploring how the circadian system’s sensitivity to light may predispose individuals to DSPD, and the genetic basis for individual differences in light sensitivity.
“The virtually ubiquitous use of light-emitting electronic devices may be wreaking havoc with our circadian systems, especially in people who are more sensitive to light,” says Dr Cain.