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10 things to know about sleep as the clocks go back

From BBC - October 27, 2017

People across the UK will wake up having gained an hour's sleep on Sunday morning, as the clocks go back heralding darker evenings and shorter days. But how much do we know about sleep and its impact on our lives, from our health and mood, to how long we will live?

1. We are told to get our eight hours

We often hear that we should all be getting eight hours' sleep a night. Organisations from the NHS to the US National Sleep Foundation recommend it. But where does this advice come from?

Studies carried out around the world, looking at how often diseases occur in different groups of people across a population, have come to the same conclusion: both short sleepers and long sleepers are more likely to have a range of diseases, and to live shorter lives.

But it's hard to tell whether it is short sleep that is causing disease or whether it is a symptom of a less healthy lifestyle.

Short sleepers are generally defined as those who regularly get less than six hours' sleep and long sleepers generally more than nine or 10 hours' a night.

Pre-puberty, children are recommended to get as much as 11 hours' sleep a night, however, and up to 18 hours a day for newborn babies. Teenagers should sleep for up to 10 hours a night.

Shane O'Mara, professor of experimental brain research at Trinity College Dublin, says that, while it's difficult to tell whether poor sleep is a cause or a symptom of poor health, these relationships feed off each other.

For example, people who are less fit exercise less, which leads people to sleep badly, become exhausted and less likely to exercise, and so on.

We do know that chronic sleep deprivation - that is, under-sleeping by an hour or two a night over a period of time - has been linked time and again by scientists to poor health outcomes: you do not have to go for days without sleep to suffer these negative effects.

2. What happens in your body when you do not sleep enough?

Poor sleep has been linked to a whole range of disorders.

A review of 153 studies with a total of more than five million participants found short sleep was significantly associated with diabetes, high blood pressure, cardiovascular disease, coronary heart disease and obesity.

Studies have shown that depriving people of enough sleep for only a few nights in a row can be enough to put healthy adults into a pre-diabetic state. These moderate levels of sleep deprivation damaged their bodies' ability to control blood glucose levels.

Vaccines are less effective when we are sleep deprived, and sleep deprivation suppresses our immune system making us more prone to infection.

One study found participants who had fewer than seven hours of sleep were almost three times more likely to develop a cold than those who slept for seven hours or more.

People who do not sleep enough also appear to produce too much of the hormone ghrelin, associated with feeling hungry, and not enough of the hormone leptin, associated with feeling full, which may contribute to their risk of obesity.

There are also links to brain function and even in the long term to dementia.

Prof O'Mara explains that toxic debris builds up in your brain during the course of the day and waste is drained from the body during sleep. If you do not sleep enough, you end up in a mildly concussed state, he says.

The impact of sleeping too much is less understood, but we do know it is linked to poorer health including a higher risk of cognitive decline in older adults.

3. We need different types of sleep to repair ourselves

After we fall asleep we go through cycles of "sleep stages", each cycle lasting between 60 and 100 minutes. Each stage plays a different role in the many processes that happen in our body during sleep.

The first stage in each cycle is a drowsy, relaxed state between being awake and sleeping - breathing slows, muscles relax, the heart rate drops.

The second stage is a slightly deeper sleep - you may feel awake and this means that, on many nights, you may be asleep and not know it.

Stage three is deep sleep. It is very hard to wake up during this period because it is when there is the lowest amount of activity in your body.

Stages two and three together are known as slow wave sleep which is usually dreamless.

After deep sleep we go back to stage two for a few minutes, and then enter dream sleep, also called REM (rapid eye movement). As the name suggests, this is when dreaming happens.

In a full sleep cycle a person goes through all the stages of sleep from one to three, then back down to two briefly, before entering REM sleep.

Later cycles have longer periods of REM, so cutting sleep short has a disproportionately large effect on REM.

4. Shift workers who have disturbed sleep get sick more often

Shift work has been associated with a host of health problems. Researchers have found shift workers who get too little sleep at the wrong time of day may be increasing their risk of diabetes and obesity.

Shift workers are significantly more likely to report "fair or bad" general health according to a 2013 NHS study, which also found people in this group were a lot more likely to have a "limiting longstanding illness" than those who do not work shifts.

People who work shifts are significantly more likely to take time off sick, according to figures from the Office for National Statistics.

There is a far bigger gap for non-manual workers than manual workers - lack of sleep seems to have a bigger impact on those doing more sedentary jobs.

5. And many of us are feeling more sleep deprived than ever

To judge from media reports, you'd think we were in the grip of a sleeplessness epidemic. But are we really all more sleep deprived than before?

A big piece of research looking at data from 15 countries found a very mixed picture. Six showed decreased sleep duration, seven increased sleep duration and two countries had mixed results.

Lots of a evidence suggests the amount we sleep has not changed that much in recent generations.

But if you ask people how sleep deprived they think they are, a different picture emerges.

So why do so many people report feeling tired?

It may be that this problem is concentrated in certain groups, making the trend harder to pick up on a population-wide level.

Sleep problems vary considerably by age and gender, according to one study of 2,000 British adults. It found women at almost every age have more difficulty getting enough sleep than men.

The sexes are more or less level at adolescence but women begin to feel significantly more sleep deprived than men during the years where they may have young children, while work may become more demanding. The gap then shrinks again later in life.

Caffeine and alcohol both affect sleep duration and quality.

6. But we did not necessarily always sleep this way

7. Phones are keeping teenagers awake

8. Testing for sleep disorders is on the up

9. Are other countries doing it differently?

10. Morning larks, night owls?

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