Falling asleep in the armchair in front of the television is seen to be as much a part of growing old as getting grey hair and going bald. But now Scots scientists have unravelled the biology behind why those entering their golden years tend to nod off in the middle of the afternoon.
Researchers at Glasgow University have found daylight triggers our brains to produce specific chemicals that keep us awake. When functioning normally, concentrations of these neurotransmitters fall as it gets dark, regulating our sleep patterns to the night-time.
But as we get older, the brain produces less of these chemicals and the body becomes less sensitive to them, making it harder for the body to tell the right time to sleep.
Dr Stephany Biello, a psychologist who led the research, claims this leads to a lack of quality sleep that the body needs to repair itself and can prevent the immune system from functioning properly.
She now hopes to develop drugs and treatments that can be used to reset the internal clock - known as circadian rhythm - that controls people’s sleep patterns.
"In the laboratory, we found that using brighter lights increased the neurotransmitter signal and when we increased the neurotransmitter concentration it produced a greater response," said Biello.
Biello plans to publish her findings later this year. She now hopes to investigate if particular wavelengths of light trigger greater responses than others. She will also investigate ways of making the neurotransmitter more effective in older patients.
She added: "Problems in synchronising this internal clock is the main reason why people over 65 have problems sleeping. It can have a serious impact on their quality of life as they are not sleeping properly at night and so fall asleep during the day. But, more seriously, it can cause the immune system not to function properly."
Sleep deprivation is known to cause a drastic reduction in the immune cells in the blood that protect the body from infection. Scientists believe hormones produced during certain stages of the sleep regulate the production of these cells.
Around half of elderly people show significant disruption to their regular sleep patterns and more than 1.5 million people in the UK use sleeping pills.
Dr James Goodwin, head of research at Research into Ageing, which is celebrating its 30th anniversary this year, said: "
We are confident this research will contribute to new understanding of how sleep is influenced by age, which could potentially improve millions of older people’s lives."