Discovery that body temperature has a vital role in the onset of sleep

May 28 2004

Insomnia affects up to a quarter of the population in Australia and can have a severe impact on the quality of life and health of long term chronic sufferers, who often cannot stay alert enough to remain in the workforce.

A breakthrough by researchers at the University of South Australia is helping to get to the core of sleep problems, with the discovery that body temperature has a vital role in the onset of sleep.

The research shows that the body needs to drop its core temperature in order for sleep to initiate normally, according to Research Fellow Dr Cameron van den Heuvel at UniSA’s Centre for Sleep Research.

“About one to one and a half hours before falling sleep, the body starts to lose heat from its central core and that brings on increased feelings of tiredness in normal healthy adults. These physiological changes happen well before going to bed and may be occurring before people realise them,” Dr van den Heuvel said.

“Temperature regulation is a significant factor in each of the two types of insomnia. The difference is when the insomnia occurs. People with sleep onset insomnia have difficulty initiating sleep at the beginning of the night, taking two to four hours each night in the worst cases; while people with sleep maintenance insomnia fall asleep easily but have trouble staying asleep, waking up multiple times during the night. Sleep onset insomnia is most common in the 20-30 year age range whereas sleep maintenance insomnia affects mostly retirees and the elderly. In both types of insomnia, sleep is not restful and sufferers are tired during the day.

“Studies of sleep onset insomniacs show that they consistently have a warmer core body temperature immediately before initiating sleep, when compared with normal healthy adults. This results in a state of heightened arousal that prevents them from falling asleep when they go to bed, probably because they have to wait for their bodies to lose the heat that’s keeping them awake. We’re only talking about a half to one degree but that small temperature change can result in significant differences in arousal between insomniacs and people without sleeping problems.

“While sleeping tablets are effective in some people some of the time, many insomniacs have impaired thermo-regulatory systems that limit their ability to lose heat and affect their responses to commonly prescribed drugs that would normally increase sleepiness,” Dr van den Heuvel said.

“When used by healthy young adults these drugs cause them to lose heat, become sleepier and fall asleep. This temperature change is important for the drugs to work successfully and is consistent across a range of drugs that we’ve investigated.

“To drop the core temperature, the body needs to act like a radiator, with heat from the central core transferring to areas such as the hands, face and feet, causing the peripheral skin temperature to rise and then lose heat to the surrounding environment,” Dr van den Heuvel said.

In a significant breakthrough, UniSA researchers have discovered that the failure by insomniacs to regulate their core temperature sufficiently can be narrowed down to an inability to lose heat from their periphery.

“The exciting part of this research, funded by the National Health & Medical Research Council, is that these results may provide a new therapeutic target, whether it is by drugs or another mechanism that we can potentially exploit,” Dr van den Heuvel said.

One mechanism called biofeedback being researched by UniSA psychologist, Dr Kurt Lushington, involves training people to raise or lower their hand temperature by visualising images such as lying on a beach. Some 75-80 per cent of those studied successfully raised or lowered their temperature by one and a half degrees or more. The next step will be to enrol insomniacs in a similar study to determine its suitability as a treatment.

Dr van den Heuvel said that thermoregulatory changes were not always the primary cause of insomnia. Conditions such as pain, anxiety and depression could also cause disturbed sleep and when these were treated, normal sleep was typically restored.