How much screen time is too much? Effects on your eyes, sleep and body

Is there a safe amount of screen time?

For adults, there is no official daily screen-time limit. The WHO’s 2020 guidelines don’t give adults a number of hours. They recommend limiting time spent sitting, and replacing it with movement of any intensity.

That matters, because “screen time” isn’t one thing. Two hours of video calls for work, two hours of scrolling in bed at midnight, and two hours watching a film with family affect you in different ways. A better question than how many hours is what is the screen doing to your eyes, your sleep and your movement. Those three are where the research is clearest.

1. Your eyes: digital eye strain

Tired, dry or burning eyes, blurred vision and headaches after long screen sessions have a name: digital eye strain, also called computer vision syndrome. A 2018 review in BMJ Open Ophthalmology found it is very common in people who use screens for long periods.

Two things drive it:

• You blink less. When you concentrate on a screen, you blink less often and less completely, so the tear film on your eyes dries out.
• Your focusing muscles work non-stop. Looking at something close for a long time keeps the muscles inside your eye contracted.

What helps:

• The 20-20-20 rule. Every 20 minutes, look at something about 20 feet (6 metres) away for 20 seconds. It is commonly recommended to give your eyes regular breaks.
• Set up your screen. Keep it about an arm’s length away, with the top at or slightly below eye level. Reduce glare from windows and overhead lights.
• Blink on purpose, and use lubricating eye drops if your eyes feel dry.
• Get an eye test if it has been more than two years. An uncorrected or outdated prescription makes strain much worse.

What doesn’t help much: blue-light glasses. A 2023 Cochrane review found they probably make no difference to eye strain from computer use in the short term, and the evidence on sleep was uncertain.

See a doctor urgently for eye pain, sudden blurred or lost vision, or new flashes or floaters. More on this in our guide to eye strain from screens.

2. Your sleep: screens before bed

Screens before bed affect sleep in two ways: the light, and the fact that the content keeps your brain alert.

In a study in PNAS, adults who read on a light-emitting tablet for about four hours before bed for five nights took longer to fall asleep, released less melatonin (the hormone that makes you sleepy), had their body clock pushed later, and felt less alert the next morning than when they read a printed book.

What helps:

• Put screens away 30–60 minutes before bed, and keep the phone out of reach so you don’t pick it up when you wake at night.
• Dim screens and room lights in the evening. Night mode helps a little, but less light overall matters more than the colour.
• Get daylight in the morning. It sets your body clock earlier and makes it easier to feel sleepy at night.

Our daily routine and sleep guide builds a wind-down time from your own wake-up time.

3. Your body: hours of sitting

Most screen time happens sitting down. Long, unbroken sitting is linked to a higher risk of type 2 diabetes, heart disease and earlier death, and looking down at a phone or laptop for hours can leave your neck, shoulders and upper back stiff and sore.

What helps:

• Stand up and move for 2–3 minutes every 30 minutes. Take calls standing or walking.
• Raise your laptop on a stand or a stack of books, and use a separate keyboard, so you aren’t looking down all day.
• Meet the WHO activity target of 150–300 minutes of moderate activity a week, plus strength training twice a week.

Read more in what sitting all day does to your body and our guide to neck and back pain from desk work.

What about mental health?

You’ll often read that screens cause anxiety and depression. The evidence is less clear than the headlines. A large 2019 analysis in Nature Human Behaviour of data from more than 350,000 adolescents found that digital technology use was linked to slightly lower wellbeing, but the effect was very small, similar in size to eating potatoes regularly.

That doesn’t mean screens never matter. Doom-scrolling late at night costs you sleep, and poor sleep clearly affects mood. If you notice that a particular app leaves you feeling worse, that’s a good enough reason to use it less.

A simple screen-time checklist

1. Every 20 minutes, look 20 feet away for 20 seconds.
2. Stand up and move every 30 minutes.
3. Keep your screen at eye level and an arm’s length away.
4. Put your phone away 30–60 minutes before bed, and charge it outside the bedroom if you can.
5. Get outside in daylight every morning.
6. Get an eye test every two years, or sooner if your eyes are struggling.

References

1. 1.Digital eye strain: prevalence, measurement and amelioration. BMJ Open Ophthalmology, 2018.doi:10.1136/bmjophth-2018-000146
2. 2.Computer vision syndrome: a review of ocular causes and potential treatments. Ophthalmic and Physiological Optics, 2011.doi:10.1111/j.1475-1313.2011.00834.x
3. 3.Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 2015.doi:10.1073/pnas.1418490112
4. 4.Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults. Cochrane Database of Systematic Reviews, 2023.doi:10.1002/14651858.CD013244.pub2
5. 5.The association between adolescent well-being and digital technology use. Nature Human Behaviour, 2019.doi:10.1038/s41562-018-0506-1
6. 6.Sedentary time and its association with risk for disease incidence, mortality, and hospitalization: systematic review and meta-analysis. Annals of Internal Medicine, 2015.doi:10.7326/M14-1651
7. 7.World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 2020.doi:10.1136/bjsports-2020-102955

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Educational information, not medical advice. See a doctor for anything persistent or severe. All content is original to Venva.