By the age of 75 the average Briton will have spent more than 12 years watching television.Those aged 11 to 15 now spend 50 per cent of their waking lives – 42 hours a week, six hours a day – in front of a screen. If you turn the TV off these ill-effects can be prevented or reversed.
Our attraction to looking at anything bright and fastmoving is an evolutionary mechanism, a survival instinct.
These images on screen trigger what psychologists call attentional inertia – we are dazzled and cannot take our eyes off the screen. But it seems we pay the price for tapping into these primitive urges.
Or perhaps memory is affected, so we forget we have eaten.
Perhaps the most compelling study, from the Dunedin School of Medicine, New Zealand, was published in 2004.
These findings were backed up by a study from Birmingham University that found women who watched TV during a meal were likely to snack more in the hours after.
One theory is that screen time interrupts the release of chemicals in the blood linked to hunger and satiation.
It elicits the orienting response – our sensitivity to movement and sudden changes in vision or sound.
Studies have shown that infants, when lying on their backs on the floor, will crane their necks around 180 degrees to watch.
It's a bit like the way that those who add salt to their food find unsalted food tastes dull.