We’ve known, vaguely, for a long time that losing sleep can make us struggle to concentrate and keep smiling. Even Shakespeare knew the value of sleep, describing it as the ‘balm of hurt minds’ and the ‘chief nourisher in life’s feast’.

But research is increasingly proving that a lack of good quality sleep can seriously damage our physical and mental health. More than 20 large-scale studies have proved conclusively that the shorter your sleep, the shorter your life – and it’s not hard to see why…

How a lack of sleep affects physical health

Weight gain and obesity

Research shows that insufficient sleep is a factor in weight gain and obesity. This is probably because sleep deprivation reduces levels of leptin (the hunger-inhibiting ‘you’re full’ hormone) and increases levels of ghrelin (the hunger-stimulating hormone). It’s a vicious circle, too, as you’re more prone to sleep problems if you’re overweight.

Increased diabetes risk

People who usually sleep less than five hours a night, particularly those lacking deep or ‘slow-wave’ sleep, are at increased risk of developing diabetes. Their body processes glucose differently, reacting as though suffering from insulin resistance (a condition in which your body doesn’t react properly to insulin). Tiredness causes you to secrete more stress hormones (e.g. cortisol), making it harder for insulin to function correctly and leaving excess glucose in your bloodstream.

Increased cancer risk

Professor Matthew Walker, author of Why We Sleep, says that after just one night of only four or five hours’ sleep, your natural cancer-attacking cells drop by 70%. US researchers have discovered that when people work nights, they produce 80% less of a chemical which is a by-product of DNA tissue repair, indicating that their bodies aren’t carrying out the crucial cell restoration which should happen naturally overnight.

Increased risk of Alzheimer’s Disease

Long-term insufficient sleep significantly raises your risk of Alzheimer’s disease. During deep sleep, amyloid deposits (a toxin that accumulates in the brains of Alzheimer’s sufferers and kills surrounding cells) are ‘cleaned’ from the brain. Without sufficient sleep, these plaques build up, especially in deep-sleep-generating regions – meaning you sleep even less and are even less able to destroy the plaques. It’s a vicious circle.

Increased risk of heart disease, heart attack and stroke

Persistent sleep deprivation is associated with increased heart rate and blood pressure and higher levels of inflammation, which can all put extra strain on your heart. Over-45s who sleep less than six hours a night are 200% more likely to have a heart attack or stroke.

Weakened immunity

Sleep deprivation damages production and distribution of immune factors.

Reduced fertility and libido

Research has revealed that men and women who don’t get enough quality sleep have lower libido and less of an interest in sex. This may partly be linked to sleep apnoea, which disturbs sleep, as men who suffer from sleep apnoea also tend to have lower testosterone levels, which can lower libido. Regular sleep disruption can also reduce the secretion of reproductive hormones.

How a lack of sleep affects mental health

Increased risk of depression and anxiety

Many studies have linked anxiety and depression to poor quality and insufficient sleep. Daniel Freeman, co-author of major research on the link between mental health and sleep published in Lancet Psychiatry, says that having insomnia doubles your chances of developing depression and that treating insomnia is shown to reduce depression.

Increased risk of paranoia, hallucinations and psychotic episodes

The same study also showed that when people sleep better, they’re far less likely to suffer from paranoia, hallucinations or psychotic episodes. General mental health is much improved in people given therapy to improve their sleep.

Reduced memory, concentration and reaction times

While we can usually cope with the odd late or broken night, the effect on our mental health and abilities becomes far more pronounced after several nights or frequent occurrences of poor sleep.

Your ability to concentrate and make decisions will decline and your reaction times will slow significantly. This can be dangerous, affecting not only your health and safety, but that of others you work with, care for – or drive past.

Studies show that sleep deficiency harms your driving ability as much as, or more than, being drunk. Less than five hours’ sleep? You’re 4.3 times more likely to be involved in a crash. Four hours’ sleep? 11.5 times more likely. It’s estimated that driver fatigue is responsible for around 100,000 car accidents and 1,500 deaths each year.

A Change of Attitude

“No aspect of our biology is left unscathed by sleep deprivation,” says Professor Walker, who fears sleep loss is costing the NHS and our economy dearly. “Things have to change: in the workplace and our communities, our homes and families.” He believes that sleep “needs to be prioritised, even incentivised” and that we have “stigmatised sleep with the label of laziness” because we want to seem busy; “It’s a badge of honour.” That’s an attitude we need to change.