ACCORDING to a survey by the British Airline Pilots Association, 43pc of pilots believe their ability to fly is regularly impaired by tiredness. And a recent report of two pilots falling asleep mid-flight may not be a unique event, as 29pc of pilots in the survey reported having had similar experiences.
On the ground, according to research by the UK government, 10pc of road traffic accidents may be due to fatigue caused by lack of sleep. Inadequate sleep can also cause memory problems, depression and a weakening of the immune system. But it's the link between lack of sleep and chronic disease that is of most concern.
So, when the clocks go back this weekend, a lie-in should be just the thing – shouldn't it?
"Sleep deprivation is very common," says Dr Elaine Purcell of the Sleep Disorders Clinic at the Mater Private Hospital. "Over recent decades, the amount of sleep we're getting has gradually decreased from an average of 9 hours a night to an average of 6.5 hours.
"Not getting enough sleep has many adverse health consequences. It increases your heart rate, making your heart beat faster; it increases blood pressure; and, overall, it increases the risk of a heart attack."
Earlier this year, Wageningen University found that those who sleep for less than six hours have a 65pc higher risk of cardiovascular disease than those who sleep for 7 to 8 hours. And a number of studies have found that sleep deprivation increases inflammation – which also increases the risk of heart disease, particularly in women.
A link between inadequate sleep and type 2 diabetes has also been established. Type 2 diabetes, which is associated with diet and obesity, affects about 170,000 people here.
"Sleep deprivation has a strong affect on your metabolism and your appetite hormones," says Dr Purcell. "Not getting enough sleep increases your appetite hormones, making you hungrier, and if you're tired you're less likely to exercise. The combination of increased appetite, eating more and not exercising leads to weight gain and obesity."
Dr Anna Clarke, Health Promotion and Research Manager at Diabetes Ireland, explains how this can lead to type 2 diabetes.
"Type 2 diabetes is directly related to lifestyle factors that lead to increased weight of the individual. So, really, it's related to putting on weight that leads to obesity, especially if you're putting on that weight around your tummy.
"This can put you into an insulin-resistant state. This is where your body is producing insulin, but the fat cells around your abdomen absorb it before it can be used by the rest of the body."
The hormone ghrelin directly stimulates appetite. Lack of sleep produces more of the hormone, and one night of inadequate sleep is enough to trigger this process. Children and adolescents are particularly vulnerable.
But in addition to increasing appetite, lack of sleep also influences what we eat. Researchers at Columbia University used functional magnetic resonance imaging to understand how the sleep-deprived brain reacts to different kinds of food. Participants in the study had their brain activity monitored while they were shown images of a range of healthy and unhealthy foods. The researchers found that those participants who had endured five nights of four hours' sleep per night had a greater reaction in their brain's reward centres to pictures of sweet or salty foods than to pictures of healthy foods.
At the same time, a similar study was being carried out at the University of California, Berkeley. Healthy adults were deprived of sleep and asked to rate different foods while their brain activity was being monitored. The Berkeley researchers found that lack of sleep interfered with the parts of the brain used in decision making, which meant the sleep deprived participants were more likely to choose unhealthy foods.
So, can a Sunday morning lie-in undo some of this? Not according to Dr Purcell.
"If you're sleeping for long periods over the weekend, getting up 4 or 5 hours later than you normally would, that's the equivalent of giving yourself 4 or 5 hours of jet lag," she says. "You can start to introduce a body clock problem, and it can be harder to fall asleep that night.
'THIS is very common with the Sunday morning sleep-in after a Saturday night out. It can then be very hard to get to sleep on Sunday night, so you're getting up on Monday morning even more sleep-deprived."
In a study by the University of Pennsylvania School of Medicine, participants were allowed only four hours of sleep a night for five consecutive nights. Each day, at two-hour intervals, participants' attention, reactions times, fatigue and sleepiness levels were assessed.
Unsurprisingly, after only four hours' sleep participants were feeling sleepy and fatigued and they suffered lapses in attention and slower reaction times.
And each night of restricted sleep had a cumulative effect on this tiredness and mental impairment. After five nights of restricted sleep participants were given a night of recovery sleep.
The amount of sleep varied, but even those who had the maximum 10 hours failed to fully reduce their fatigue or restore mental performance.
A similar study by Dr Alexandros N Vgontzas at Penn State College of Medicine found that even six hours sleep per night was enough to impair mental performance, and that two nights of recovery sleep still wasn't enough to restore mental performance.
"The usual practice of extending sleep during the weekend after a busy work-week associated with mild sleep deprivation is not adequate in reversing the cumulative effects on cognitive function resulting from this mild sleep deprivation," said Dr Vgontzas at the time of the study.
However, Dr Vgontzas found that women were better able to handle mild sleep deprivation. They reported less fatigue and less mental impairment during the periods of restricted sleep, and they showed greater improvement after two nights of recovery sleep.
So, it's apparent we need more sleep. But how much do we need? Researchers at the Universite Laval in Quebec analysed the habits of 276 people over six years. They found that those who slept less than seven hours and those who slept more than eight hours were twice as likely to develop type 2 diabetes than those who slept between seven and eight hours.
A LARGER study of 54,000 people by the Centre for Disease Control and Prevention in the US found that those who slept in excess of 10 hours a night were at an elevated risk of coronary heart disease, stroke and diabetes.
Commenting on the results of the study, Dr M Safwan Badr, president of the American Academy of Sleep, said: "Sleeping longer doesn't necessarily mean you're sleeping well. It is important to understand that both the quality and the quantity of sleep impact your health."
Dr Purcell agrees. She also believes that, while excessive sleep may lead to chronic health problems, it may also be a symptom of an existing problem.
"Generally, when someone's consistently sleeping for more than nine hours, you would consider the possibility of a sleep disorder," she says. "There are many sleep disorders that cause excessive sleepiness. The most common, by far, would be sleep apnoea."
Other conditions include narcolepsy – which is rare – and restless leg syndrome. Alcohol and some medications also cause excessive sleepiness.
So, is there a right amount of sleep? At the Universite Laval, they found that seven to eight hours seemed to provide the best protection "against common diseases and premature death".
But, it's not just about the numbers. "A healthy, balanced lifestyle is not limited to diet and fitness; when and how you sleep is just as important as what you eat or how you exercise," says Dr Badr.
"Normally people just went to bed and turned off the lights," says Dr Purcell. "Now we're playing on our iPhones and iPads. They keep us up later than we should be."
Don't have a lie-in this weekend – start a new regime of getting to bed early and actually going to sleep.
More advice at www.diabetes.ie or www.materprivate.ie/service/ sleep-disorders-clinic