According to a report from the Royal Society for Public Health, four in ten of us aren’t getting enough sleep, while one in five sleep poorly most nights. Many of us under-sleep by an hour a night, which adds up to a whole night’s missed sleep every. So what’s stopping us getting the sleep we need?

1 Exposure to light

Before the invention of artificial lighting, our favourite way to while away the evening was to sleep. Records show that in the Middle Ages, we’d head for bed shortly after dusk, wake in the middle of night for a couple of hours, then sleep again until daylight.

But in the late 1600s, the first street lighting was introduced, using wax candles in glass lamps, and it became fashionable to socialise in the evenings. We started going to bed later, and dropping our ‘second’ sleep. And sleep-times have been getting shorter ever since. Long work hours, more shift-work, long commutes, global communication across multiple time zones, and the 24-hour availability of almost everything means we sleep less now than any other time in recent history.

Exposure to light also plays a key role in regulating our natural sleep-wake cycles – scientists at Oxford University recently discovered that there is a separate sensor in the eyes which grabs light specifically to regulate the body clock. Exposure to bright artificial light means we’re low awake long after when our ancestors would be crawling into their caves to sleep. Brain imaging following light exposure shows increased activity in many areas of the brain involved in alertness, cognition, memory and mood. Inappropriately timed light exposure can therefore disrupt not only sleep and circadian timing, but also levels of alertness, performance and mood.

The bright light from a computer mimics morning light, making you feel awake, so dim the lights on computer and phones screens in the evening. Keep the background lighting soft, and don’t sit too near the TV screen. Being exposed to bright lights late at night pushes the body clock later which can make it more difficult to fall asleep at bedtime and get up in the morning. According to recent research, even a dim light in your bedroom (from a clock radio or even the standby button of a TV) could potentially interfere with the chemical structure of your brain. If you can’t block out all light, try sleeping with an eye mask. If you have to get up in the night, avoid putting on any lights (keep a torch by your bed or nightlight in the hall). Even a short burst of brightness can temporarily suppress your body’s production of melatonin.

2 Social jet lag

Our natural sleep patterns are determined by the body or circadian clock, the 24-hour cycle of biological processes that exists in both animals and plants. And while it used to be thought that the body clock was in the hypothalamus, a grape-sized nodule at the base of the brain, we now know that there is a body clock gene in every cell of the body. It’s these cells that directly influence the rhythms of the heart, lungs, liver and other organs – cranking up your metabolism and raising your body temperature when you need to be alert, and winding it down when it’s time to rest.

Working alongside the circadian rhythm is a process known as ‘sleep pressure’ which builds up the longer you stay awake. It’s particularly dangerous to be awake between 3am and 6am, when the circadian rhythm of sleepiness is at its peak, coupled with a build-up of sleep pressure because of the extended awake time. Shift-workers, doctors, firefighters and other professionals are particularly vulnerable to sleepiness-related accidents. A recent study from Stanford University found that the body clocks of people suffering from depression were so out of sync with their daily lives, it was as if they were living in a difference time zone. The study researchers say it could lead to potential breakthroughs in both how we predict and how we treat depression.

The interaction of these two rhythms also causes the ‘post-lunch’ dip. Shorter and later sleep at night leads to greater sleep pressure in the day, which cannot be counteracted by the circadian rhythm, which has shifted later by exposure to artificial light during the evening. If you add a heavy lunch, your chances of staying awake are low!

Living out of sync with the natural circadian rhythm can take its impact on health. Forcing your body to be alert and active at a time it should be asleep triggers a stress response in the body that lowers the immune system, and puts strain on the heart.

Timing your light exposure is the most powerful way to affect your body clock. Morning light is essential for synchronising our internal body on a daily basis. It can boost alertness and mood, and affect different levels of hormones . Exposure to light early the morning is crucial as it signals to your body that the day has begun, which stops the production of the sleepy hormone melatonin, and increases cortisol, the ‘awake’ hormone.

It’s tempting to catch up on sleep at weekends, but if you can, stick to the same routine seven days a week to avoid ‘social jet lag’ on Monday mornings. Have a nap after lunch to boost energy levels instead, but no longer than 20 minutes.

3 Your genes

Convinced you’re a natural lark or night owl? Scientists at the University of Surrey have discovered a gene, called Period-3, which comes in a long and short version. We all get two copies of the gene, one from our mother and one from our father. Around 10 per cent of the population who have two long versions of the gene tend to be naturally early risers, while between 10 and 15 per cent have two short copies which makes them night owls.

But the rest of the population have both long and short, which means that it’s our daily habits that determine whether you become a lark or owl. So for most of us, staying up late is more likely to be a habit than an innate drive In a recent Colorado University study, a group of ‘night owls’ camped outdoors for a week with no electric lights or torches. Within a week the body clocks of the whole group had shifted – on the whole, they went to sleep two hours earlier (around 10pm instead of midnight), and woke two hours earlier (6am instead of 8am). The key is the increased exposure to sunlight they had on the trip – around 400 per cent more than normal. Light exposure is crucial to regulating the body clock, especially in the early part of the day. Light is measured in lux and at home or work, you’re exposed to around 50lux. Outside, however, you get between 10,000 and 25,000 lux. So make time for a walk early in the day.

4 Getting older

Sleep patterns change throughout life, with distinct ‘ages’ of sleep occurring in babies, children, adolescence and young adulthood, middle-age and later life. As much as 16 hours a day may be spent asleep in the first few weeks of a baby’s life. It’s thought that sleep is vital for cognitive development, allowing them to consolidate the vast amount of information they take in from the world around them. Over the next few months, sleep patterns gradually consolidate into fewer but longer bouts. By six months, a 24-cycle is beginning to emerge of a long sleep at night, and shorter day-time naps.

Brain development means that children continue to need as much sleep as possible as they grow up. Young children sleep between 11 and 12 hours a night, reducing as they get older to around 8-9 hours by their early teens. A 12-year-old will be tired at 10 o’clock – that time is pushed back by 20 minutes every year until at 20, he feels tired at midnight.’

Sleep patterns change dramatically during adolescence, as teenagers experience a two to three hour change in the timing of their clocks, going to bed later and waking later. Teenagers are essentially living in another time zone so having them get up for school at 7am is like asking adults to wake at 4am. It’s not surprising that teenagers are unresponsive and irritated.

Then, at the age of 21, the body clock starts to shift back again. By the age of 50, people are waking up at the sort of early-morning hour they woke at when they were young children. In middle-age, the risk of clinical sleep disorders increases for women, partly due to menopausal night sweats and mood disorders – post menopausal women have nearly double the rate of insomnia complaints as pre-menopausal women. Weight gain (which can trigger breathing problems at night) and the stresses of life also disrupts sleep at this age.

Sleep problems increase for both sexes as we age – we’re more likely to experience broken sleep as we get older, and rely more on daytime naps. It takes older people a little longer to fall asleep, and there is a reduction in sleep ‘depth’ with less REM sleep.

Whatever your age, staying active can help. Research shows people sleep better if they are active for 150 minutes a week (around 20 minutes a day, or 30 minutes five times a week). But avoid strenuous activity late in the evening as it has the opposite effect, keeping you awake. And if you really want to sleep well, avoid alcohol. It may make you feel sleepy, but even a small amount of alcohol can interfere with the normal sleep process.

5 Society pressures
‘I’ll sleep when I die’. ‘Sleep is for wimps’. There’s still a badge of honour in not sleeping much. But research is showing that having your sleep cycle disrupted by shift work over a long period of time raises your risk of high blood pressure, diabetes, depression, cancer, heart attack and stroke. It may also affect the immune system, leaving you more vulnerable to viruses and infections, and impact on the health of the brain, raising your risk of Alzheimer’s. Lack of sleep also makes you less emotionally and psychologically resilient, so stress is more likely to become anxiety, and low mood to turn into depression. So rather than admiring people who get by on as little sleep as possible, to live our best life, we need to treat healthy sleep habits as seriously as eating a balanced diet and getting regular exercise.

The Sleep Cycle

• We sleep in 90-minute cycles throughout the night.
• 75% of our sleep is called NREM (non-rapid eye movement sleep). This comes in four stages.
• Stage 1 is very light sleep when we are easily woken up. It lasts around 7 minutes.
• Stage 2 is deeper sleep, when we might have the sensation of ‘falling’ and jerk awake. This lasts around 12-15 minutes.
• Stages 3 and 4 bring deeper, more restorative sleep, when muscles relax, tissue growth and repair occurs, hormone levels are replenished, and the body builds up energy for the next day. The brain waves slow right down as blood is redirected to the muscles. This lasts around 30 minutes. It’s this stage we miss out on when we cut back on sleep, and some studies have found that missing out on this stage of sleep is linked with weight gain.
• REM (rapid eye movement) is the final stage of sleep, when the brain is very active, the eyes dart back and forwards, and dreams occur. The body is paralysed at this point to stop us acting out our dreams. It is thought that this stage helps ‘process’ memories and improve brain performance the next day. The first cycle of REM lasts ten minutes, but it gets longer with each cycle, finally lasting for up to an hour. Lack of REM sleep can make it difficult to concentrate and may impair memory. It’s also thought that alcohol suppresses REM sleep, which is why brain fog is a common symptom of a hangover. You also tend to miss out on REM sleep when you cut back on sleep.