Why can’t we sleep when the weather is warm?

Have you been tossing and turning in bed on a hot night? Wondered about the effectiveness of a nightcap in an attempt to chase the all-important zeds and set into motion the restorative power of sleep?

Sleep researcher from the University of Melbourne’s School of Psychological Sciences Christian Nicholas explains that our sleep/wake cycles are set by our hormones and brain neurotransmitters that together finely tune our 24-hour body clock or the circadian rhythm.

“These rhythms are modulated by external factors like sunlight and temperature,” Dr Nicholas says, “even though our core body temperature fluctuates around the 37 degrees Celsius mark, and the pattern of fluctuations is part of our circadian rhythm. 

“Body temperature is at its highest in the early evening and lowest in the early morning. A mild drop in body temperature occurs in the evening, which helps induce sleep. An accompanying series of neurological and hormonal changes help the body prepare for and then initiate that all-important, high-quality, deep restorative sleep.

“When the temperature is more extreme – very cold or very hot – the ambient temperature is further away from our core body temperature set point, making us feel uncomfortable and making it more difficult to fall asleep and stay that way.

“If you have travelled across time zones, you’ll know the feeling of jet lag. And you may be familiar with melatonin, which some people take to help reduce jet lag by shifting the circadian rhythm. Our bodies naturally secrete melatonin, and this production is supressed by light and helps you get to sleep. Which is why you often hear the advice to turn off or down TV or computer screens an hour before going to bed.”

Dr Nicholas and his local and international collaborators investigate the acute and chronic effects of alcohol and smoking on sleep by investigating brain wave patterns during sleep. The research involved testing young adults who were given vodka and orange juice to achieve a blood alcohol level of 0.1 per cent. They were monitored with electrodes placed on their scalps to measure their sleeping brainwave patterns or electroencephalogram (EEG).

“Alcohol seems to produce brain waves associated with poor or unrefreshing sleep,” he says. “These patterns have also been seen in individuals with chronic pain conditions, fibromyalgia and depression. So if sleep is being disrupted regularly by pre-sleep alcohol consumption, particularly over long periods of time, this could have significant detrimental effects on daytime wellbeing and neurocognitive function such as learning and memory processes,” Dr Nicholas says.

“While alcohol, which is commonly used as a sleep aid, may help you to get off to sleep a little quicker, the evidence shows it actually considerably disrupts and reduces the amount and quality of sleep you get.”

www.psych.unimelb.edu.au