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Screens stymie sleep

27 August 2012

There has been an explosion on the amount of screens in our lives these days. Twenty years ago the average home contained a television screen, apart from that the other screens were mainly intended as a deterrent to flies. Now not only are the television screens bigger and there are more of them in every home, there are phones, computers, games, pods, pads, and tablets all employing screens. “Screen-time” is no longer just what actors crave, it is a description of how we occupy ourselves. Just like fire and the wheel before it, the screen will have unintended consequences for humans just because we use it so much. For instance, a new study has shown that screens effect the production of hormones that regulate sleep and your body clock.

A major factor in how human sleep is regulated is exposure to light or to darkness. Exposure to light stimulates a nerve pathway from the retina in the eye to an area in the brain called the hypothalamus. In the hypothalamus the supra-chiasmatic nucleus (SCN) initiates signals to other parts of the brain that control hormones, body temperature and other functions that play a role in making you feel sleepy or wide awake. This is essentially your body clock in action.

The SCN sets off a regulated pattern of activities that affect the entire body. Once exposed to the first light each day, the SCN begins performing functions like raising body temperature and releasing stimulating hormones like cortisol. The SCN also delays the release of other hormones like melatonin, which is associated with sleep onset, until many hours later when darkness arrives.

Melatonin is a natural hormone made by your pineal gland. This is a pea-sized gland located just above the middle of the brain. During the day the pineal is inactive. When the sun goes down and darkness arrives, the pineal is turned on by the SCN and begins to actively produce melatonin, which is released into the blood. Usually, this occurs around 9 pm. As a result, melatonin levels in the blood rise sharply, you begin to feel less alert and sleep becomes more inviting. Melatonin levels in the blood stay elevated for about twelve hours before the light of a new day when they fall back to low daytime levels at about 9 am. Daytime levels of melatonin are barely detectable.

This new research has found that screen time spent in front of back-lit screens such as you find on tablet computers, lap-tops and the like, reduces melatonin levels and may impair sleep.

This research was specifically done on people using self-luminous tablet computers to read, watch movies, or play games. Participants in the study were divided into three groups. One group viewed their screen through goggles that emitted blue light. A second group watched through goggles that were orange tinted and filtered out short-wavelength light that can suppress melatonin. The last group did not wear glasses or goggles.

In each case the tablets were set to full brightness and the participants wore devices that measured the light entering the eyes.

The results showed that a two-hour exposure to light from a self-lit tablet computer screen suppressed melatonin secretion by about 22 per cent. Additionally, the longer the exposure to the screen and the closer the user to the screen the greater the reduction in melatonin.

There was a wide variation in how much light the devices emitted so the researchers recommended that, given the impact on melatonin and therefore sleep, screens should be configured to reduce brightness and their use should be limited before bed.

It also highlights the point that a tablet is never the answer to sleep problems.