Forty winks after lunch improves alertness, writes MUIRIS HOUSTON
IT’S A REASONABLE bet that many of you reading the column today will have new year health resolutions in mind. But how many of you have included a desire along the lines of: “I would like to sleep better in 2012?”
Most of us don’t get enough sleep. It used to be held that if you slept at least five hours a night, your ability to perform at your normal level wouldn’t be impaired and that you eventually adapted to less sleep.
That was never my experience. As a junior hospital doctor, I could manage reasonably well when working a single night on call, often with two to three hours of broken sleep. But when it came to obstetrics, which had a system of a week of nights with the days off, I just could not get enough sleep.
By the time the week was drawing to a close, I was like a zombie – which probably wasn’t good for me and certainly didn’t help my patients. Even with heavy-duty blackout curtains and calming music, daytime sleep was hard to come by.
But at least it ended after a week and I returned to day shifts. For parents with a baby who doesn’t sleep at night, the months and even years of broken sleep can lead to chronic tiredness, crankiness and a reduced ability to concentrate.
Is there a proven threshold below which our ability to function declines?
In 2003, researchers from the University of Pennsylvania carried out one of the longest sleep-restriction studies. For two weeks in a sleep laboratory, volunteers were allowed sleep for four, six or eight hours. They were then subjected to a test called the psychomotor vigilance task (PVT), which uses flashing numbers on a screen to assess the subjects’ ability to sustain attention. It checks for momentary lapses into sleepiness called microsleep.
Those who had eight hours of sleep hardly had any attention lapses and no cognitive decline over the 14 days of the study. But those in the four- and six-hour groups had PVT results that declined steadily.
By the sixth day, 25 per cent of the six-hour group was falling asleep at the computer. And at the end of the study, they were lapsing five times as much as they did the first day.
To complement the Pennsylvania study, scientists from the Walter Reed Army Institute of Research repeated the research using subjects restricted to odd numbers of sleep hours, at three, five, seven and nine hours.
In the seven-hour group, their response time on the PVT slowed and continued to do so for three days, before stabilising at lower levels than when they started.
The significance of this finding emerges when one considers our average sleep times. In the western world, this works out at just under seven hours on week nights. So it seems that even a consistent seven hours a night does not allow us to perform at the top of our game.
Does extra sleep on weekend nights help to make up the deficit? Previous research suggests one night alone isn’t enough. It seems we cannot beat our individual circadian rhythms, the biological clock that controls the rhythms of body temperature and growth hormone, both of which are related to sleep.
The answer may lie in purposely developing a siesta habit. It would certainly tie in with the circadian cycle, in which our bodily functions slow down naturally from 1pm to 4pm.
One Japanese study found that a 15-minute nap after lunch improved alertness and logical reasoning in a group of students who had been restricted to four hours’ sleep the night before.
Those denied an afternoon sleep did poorly in a test of cognitive function, while students who napped were at their best in mid-afternoon.
The optimum length of time for a siesta nap is probably about 30-40 minutes, while even 10 minutes’ shut-eye seems to help.
If it is something you can do on a regular basis, it might be one of the best resolutions you could make for the year ahead.