Sleep: The secret to sleeping well and waking refreshed

must know

Caffeine

• Caffeine is readily absorbed and peak concentrations occur 30-60 minutes in young adults after ingesting it. High doses slow the metabolism down and can remain in the brain for 9-15 hours.

• Percolated coffee usually contains more caffeine than instant. If the coffee grounds are boiled during preparation, as is common in Scandinavian countries, the caffeine content can be as high as 500mg per cup.

• Tea brewed directly from crushed leaves has more caffeine than tea produced with a tea bag.

• Plain chocolate contains more caffeine than milk chocolate.

Caffeine enters the bloodstream very quickly and can take between three and seven hours to leave the body. Its effects on people can be variable – some people regularly drink caffeine-laden drinks at night-time with no ill-effects; others cannot even drink one cup in the morning without it affecting them at night. Scientists believe this may be because caffeine-sensitive individuals metabolize the substance more slowly (see opposite, for factors involved in metabolizing caffeine).

Research shows that if you are not a habitual coffee drinker, the effects will be greater; and that caffeine metabolism varies with age (children, for example, tend to metabolize it more quickly).

Although caffeine is normally associated with coffee, it is found in medicines and many other foods and drinks, namely:

• tea

• chocolate, cocoa and all other chocolate-flavoured products

• over-the-counter stimulants (e.g. Pro-plus)

• painkillers (e.g. Anadin)

• herbal preparations (e.g. Guarin)

• some cola drinks

• Lucozade

• ‘energy’ drinks (e.g. Red Bull)

To find out how much caffeine you are really consuming, see the main caffeine offenders, opposite.

The absorption and metabolism of caffeine

Varied or little effect

Heredity Caffeine metabolism is controlled by many genes and racial differences exist

Gender Exercise and stress have no reliable effect on the absorption or metabolism of caffeine

Pregnancy There are no placental barriers to caffeine so the foetus is continuously exposed

Slowers-down

Oral contraceptives, late pregnancy and liver disease cause caffeine to be eliminated more slowly

It has been thought that grapefruit juice, though not other citrus juices, slows down metabolism. The data for this has now proved controversial

Some drugs like cimetidine, disulfiram, even alcohol, may slow down caffeine metabolism

Speeders-up

Smoking induces liver enzymes which break caffeine down

Rifamprin

The main caffeine offenders

did you know?

Coffee is an ancient commodity. In AD 575, about 500 years before it became a hot beverage, the crushed beans were mixed with fat and used by Ethiopian mountain warriors to provide an energy boost during long treks and warfare.

must know

Sugar

Sugar does not give you energy. A study carried out at Loughborough University, UK evaluated the energy-giving effects of sugar on ten healthy young adults. Their sleep was restricted to five hours the night before so that they would be sleepy in the afternoon, and half were given a ‘high-energy’ drink containing high levels of sugar but low levels of caffeine, and the other half a drink containing low levels of both. When submitted to vigilence and sleepiness tests the high-sugar drinkers made twice as many errors and showed higher levels of sleepiness than the control group, as well as delayed reaction times.

Sugar

Sugar can have a negative impact on sleep patterns because of its effect on insulin and blood sugar levels. It is released into the bloodstream to give you that instant ‘high’, but then departs from your system just as quickly, leaving you exhausted. In fact, you feel so tired that your instant impulse is to have yet another sugar fix to make you feel better. And so the cycle goes on. The continuing effect of these highs and lows can leave you feeling drained, or – depending on when you last had your sugar dose – over-excited, with pounding palpitations that stop you from sleeping. The disruptive impact on blood sugar levels can also cause sleep-disrupting hormonal imbalances in women. Sugar is found not only in biscuits and sweets, but also in fizzy drinks, refined wheat, tomato ketchup, baked beans and many processed foods. Read all food labels carefully.

‘Good sleep’ foods

There is some evidence to suggest that eating slowrelease energy foods, or low glycaemic index foods, (foods that keep blood sugar levels stable), may improve general health and sleep quality (as well as helping the individual to lose fat). The idea is that the lower the glycaemic rating of a particular food, the more slowly energy, in the form of glucose, will be released into the body (see Low glycaemic index foods, opposite). Thus glucose and insulin levels are prevented from plummeting during the night, which may be beneficial for sleep. Foods such as turkey and dairy products may also be helpful, as they are high in tryptophan – the amino acid that the body uses to produce the sleep-inducing hormones serotonin and melatonin (see pages 16-17).

Low glycaemic index foods

What to eat when

When we eat can be as important as what we eat. This is a question of balance. Hunger can keep you awake, so having a light snack before you go to bed can be advisable. On the other hand, going to bed with a stomach that is over-full may cause indigestion and feelings of discomfort that will keep you awake all night, especially if you have eaten fatty and rich foods that make your digestive system work harder.

must know

Diet

Studies on the effect of milky or malted drinks on sleep appeared to show benefits. However, evidence does suggest that non-milky herbal teas are just as effective in promoting a good night’s sleep.

As a rule it is best to eat your main meal at lunch time or early evening, and to eat small amounts of light food at night-time. Snacking if you wake during the night is not a good idea. Your body may come to expect food at this time, and you will carry on waking up in the night to satisfy your hunger.

Lifestyle

The way we live can provide a crucial pointer to our sleep problems. Stress, shift work, smoking and jet lag can all be contributing factors. It can be hard to change the habits of a lifetime, but when it comes to sleep, small changes can go a long way.

must know

Sleep in ex-smokers

Sleep disturbances and related daytime symptoms may leave the ex-smoker less able to cope with everyday stress, therefore increasing the likelihood of relapse. Studies have found that ex-smokers complaining of broken sleep are the most vulnerable.

Stress

This is by far the most common cause of insomnia, and can be short-term (caused, say, by the arrival of a new baby) or prolonged (juggling a career and family, or caring for someone who is ill).

Stress has been with us since ancient times, when our forebears used the natural ‘fight or flight’ response to deal with threatening situations such as attack. The causes of stress may be different now but the basic response is still there. ‘Fight or flight’ increases breathing rate, heart beat, and the production of the stress hormones cortisol and adrenaline; mental awareness is heightened and blood rushes to the muscles; the body is on red alert to deal with whatever crisis it is faced with. Doctors acknowledge that we all need some degree of fight or flight in our lives because it satisfies a primitive urge for survival. But prolonged stress can have damaging effects on both health and sleep. It is well documented that long-term stress can lead to anxiety and depression – two major sleep disruptors that can be the cause of many sleep-related disorders (see Chapter 6). Acknowledging when things have got out of hand and taking stress-relieving measures is the only solution (see Chapter 5).

Smoking

Despite the well-known risks of smoking, this still remains a major problem – mostly due to the highly addictive nature of nicotine itself, which can make it extremely difficult for habitual smokers to stop. Withdrawal symptoms can begin quickly – often within a few hours of the last cigarette – leading to sleep disturbances. The brain’s nicotine receptors respond very rapidly to the lack of nicotine, which is why for habitual smokers the first cigarette of the day can bring the most relief, even though smoking in the night can cause disrupted sleep.

must know

NRT

Nicotine replacement therapy (NRT), which reduces the urge to smoke, is recognized as an effective aid to stop smoking, and increases cessation rates. Unfortunately, nicotine patches can sometimes be over-stimulating, leading to insomnia. The 24-hour patches are less problematic than the 16-hour ones, however.

The combined impact of the brain’s response to the lack of nicotine and the breathing problems that all smokers invariably suffer from mean that nicotine is most definitely not good for sleep.

Sadly, smoking is a vicious cycle that creates numerous problems. Many people start the habit because they find it useful for maintaining or increasing their alertness. (When inhaled, nicotine quickly stimulates the heart, brain and adrenal glands.) This is particularly true among young people and sufferers of sleep-related disorders. The need to boost alertness with nicotine reinforces the use of tobacco. Tobacco disturbs sleep, reducing daytime alertness, which in turn reinforces the use of tobacco. Apart from keeping you awake, there is evidence to suggest that nicotine may affect sleep in other, more indirect ways too. Smoking is believed to affect blood sugar levels, which can make you irritable, and smokers are also statistically more likely to be coffee-drinkers, the combined effect of nicotine and caffeine having a disastrous long-term impact on sleep duration and quality.

Environment

Studies have shown that the sleeping environment can have a great impact on sleeping patterns. The degree of noise, vibration, light, humidity, or sharing a room with a partner who snores – all can have a significant part to play.

must know

Light and the retina

The retina consists of receptors that are sensitive to light. One group known as the ganglion cells are particularly sensitive to light, and in particular to blue light (such as that of the sky). These cells make a direct connection to the biological clock (see page 14) which controls the time that we are likely to sleep. About 20 per cent of light gets through the eyelids when the eyes are shut, which means that we can be affected by light and the time that we sleep even when we are in bed with our eyes shut!

Light

Light can have a profound effect upon our wellbeing, both consciously and unconsciously. The conscious effects of light have been known for many years. Numerous studies have shown that subjects exposed to bright light experience significant improvements in mood and a decrease in feelings of tiredness. Indeed, conditions such as Seasonal Affective Disorder (SAD – see page 17) are even treated by exposure to bright light. In recent years, scientists have learned that it is blue light (or natural skylight) that has the greatest effect on our sleeping patterns, because of the unique and very special influence it has on our internal bodyclock – the mechanism that determines what time we go to sleep at night and get up in the morning. (See The brain’s metronome, see page 16).

Any disruption to the bodyclock can lead us believe that it is daytime rather than night, and to react accordingly. Blue light, it is believed, also inhibits the night-time secretion of melatonin, the hormone that signals the onset of darkness (see page 16), thus preventing or disrupting sleep. (When it is dark, melatonin secretion rises and peaks at the darkest time and then goes down until dawn, when the biological clock is reset to wake.) The effects of blue light are unconscious.

There are also conscious effects of perceived light: the brighter the light in your bedroom, the more alert and less sleepy you will feel. Taking lux as a measurement of light intensity (see the table below), normal indoor lighting measures around 200 ‘lux’, while a cloudy day is around 10,000 ‘lux’ – significantly lighter, which makes it crucial to block it out as much as possible when you go to sleep. If you cannot control the amount of light you are exposed to and don’t want to hide your eyes with a pillow, consider using an eye mask.

did you know?

Blind or visually impaired people have no internal bodyclocks because their retinas are so damaged that light cannot enter the brain. They will therefore have no natural sense of when to get up and when to go to bed.

In recent years, street and industrial lighting has increased dramatically, which has had a great impact on normal daylight hours and in some people can have the effect of disturbing the timing of their internal clocks. Again, an eye mask, thick curtains, or curtains with extra lining may help.

The relative intensity of different forms of light

Note: Lux is a measure of the intensity of light.

must know

Decibels

Noise is measured in decibels (dB). A 3dB change is detectable but because of the scale used with decibels an increase of 3 means that the noise level has actually doubled.

There is some evidence to suggest that using coloured lighting may affect the ‘colour temperature’ of a room. Colours can be pleasing to some people and irritating for others so it is important not to be too assertive as to which are best. However, in general the warmer colours of sunset tend to be associated with deep sleep while the cooler colours of dawn are associated with darkness.

Humidity

One of the most common breathing-related sleeping disorders is asthma, which is often caused by allergens found in the faeces of house dust mites. The relative humidity of your surroundings will be the key factor that influences the prevalence of these mites, which can live in conditions where there is no liquid to drink as they can extract sufficient water from the environment if the humidity is high enough. Surveys in temperate climates show that mite prevalence varies according to seasonal fluctuations in indoor humidity. Mites are absent or rare in homes in dry climates unless use of evaporative coolers adds the moisture to the air that is necessary for their survival. Maintaining average daily indoor humidity below 50 per cent will prevent mite population growth and subsequent sleep-disrupting allergens. Even if humidity is lowered, it can take several months for all the allergens to disappear, however.

Noise

People can be awoken by neutral sounds louder than 45 decibels (dB), the equivalent to someone talking quietly (a lawnmower is around 105dB and the threshold for injury to the ear is around 140dB). However, sounds as low as 20dB (below the hearing threshold) can prevent you from falling asleep.

Conversely, continuous background sounds can be soporific and it seems that sounds even below 20dB can induce sleepiness – a clear danger for lorry and train drivers. Irregular high-frequency noise can have the opposite effect and be intrusive.

Noise table

must know

Vibrations

Vibration can affect sleep just as much as noise. It has been found that even quiet traffic noise of 50dB, when accompanied by vibrations, is more disturbing than when there is just noise. REM sleep is more affected than other stages of sleep. Performance the following day can be impaired.

Noise is a problem in many hospitals, particularly in intensive care units. Research has shown that noise in the latter does disturb sleep, and it could be argued that healing processes could be facilitated if natural sleep were promoted. Studies have shown that in neonatal intensive care units, for example, very low birth weight babies sleep more deeply and cry less if quiet hours are introduced. Playing ocean sounds to mask the noise in an intensive care unit has been found to work.

In controlled studies, traffic noise has been shown to increase the time it takes to get to sleep and to lead to greater irritability. Aircraft noise from airports can affect EEG results, showing lighter sleep. However, despite the fact that higher psychiatric hospital admission rates, GP visits and self-reported health problems have been reported near airports, the effects are highly variable from individual to individual, some being oblivious to the noise levels, others not.

Installing double- or triple-glazing in your home may help, as will wearing ear-plugs, though there is an obvious danger with the latter of possibly life-saving alarms not being heard.