The lights are off. You’re in bed, tossing and turning, worrying about the things you have to do the next day. You reach for your phone; its glowing surface turns the bedroom into a tableau of blue, grey and black. You check e-mails, scroll through Facebook, look at Twitter.

Suddenly, you look at the clock (the one on your phone, because who has an alarm clock these days?) and realise that an hour has passed and you are no closer to sleep than you were when you picked it up.

The latest science shows that your phone might be stopping you from getting enough sleep.

Research has shown that, aside from making you grumpy and listless, lack of sleep has been linked to an increased risk of physical accident, heart conditions and diabetes, among many other conditions.

Here are four reasons why you should buy an alarm clock and leave your phone to charge in another room.

Bad light
Light is fundamental to how our bodies work. According to the National Sleep Foundation: “Photoreceptors in the retina sense light and dark, signalling our brain about the status of the outside world and aligning our circadian rhythms … to the external day-night cycle.”

Inside your eyes are cells called intrinsically photosensitive retinal ganglion cells, which absorb light to set your circadian rhythm.

They are susceptible to blue light, which your smartphone gives off. So when you are checking your phone in the dead of night, you are confusing your sleep-system, by telling it that it should be awake. This is contraindicated for a good night’s sleep.

Reduced sex drive
Playing on your phone in bed, instead of talking or engaging with your partner on the other side, might be harmful to your relationship.

In a 2012 study of 2 000 British consumers, 15% responded that they had less sex because of using their phones in bed, while about half said that they stayed up surfing the Internet in bed for more than an hour, and sleeping later.

While there has been no peer-reviewed scientific study done on the connection between bed phone usage and sex drive, there have been many undertaken on sleeplessness and lack of sex drive.

A study from the University of Chicago found that too little sleep in men was linked to depleted levels of testosterone and a diminished sex drive.

Beep sleep
Sleep is not one continuous state of unconsciousness. There are two different kinds: rapid eye movement (REM) and non-REM sleep, and they alternate in cycles.

But if you leave your phone next to your bed at night, the beeping or vibrating of your phone can disrupt these cycles, even if it doesn’t wake you up completely (though this is also possible).

Stress
A large factor in non-chemical insomnia is worrying. You lie in bed worrying about money, work, relationships — being constantly near your phone and reachable can exacerbate this stress. Researchers from the University of Gothenburg in Sweden found that young adults were more likely to develop mental health disorders because of the pressure to be accessible.

“Mobile phone exposure variables [in the study] included frequency of use, but also more qualitative variables: demands on availability, perceived stressfulness of accessibility, being awakened at night by the mobile phone, and personal overuse of the mobile phone,” they wrote in an article published in the journal BMC Public Health.

Their study included more than 4 000 people between the ages of 20 and 24, and concluded: “The risk for reporting mental health symptoms at follow-up was greatest among those who had perceived accessibility via mobile phones to be stressful.”

Lead author Sara Thomée said: “Regularly using a computer late at night is associated not only with sleep disorders but also with stress and depressive symptoms in men and women.”

Harvard neuroscientist Dr Orfeu Buxton described this as “threat vigilance” because you are always aware that your phone is at hand and you feel beholden to be available to respond to whatever work or the world demands of you.