Teenagers' 'incessant' use of social media is radically reducing the time they spend sleeping and exercising – and could have a detrimental effect on mental health and wellbeing.

A large-scale study, published in The Lancet Child & Adolescent Health, explored associations between the frequency of social media use and the mental health and wellbeing in adolescents.

For the study, a group of more than 12,000 teenagers in England – aged between 13 and 16 – were interviewed over a period of three years. Teenagers were quizzed on how often they checked social-media sites such as Instagram, Facebook, Whatsapp and Twitter each day.

More than half of the girls (51 per cent) and 43 per cent of the boys in Year 9 (aged between 13 and 14) checked their social media platforms throughout the day.

By year 11 (aged 16), the proportion of frequent social media users had increased to 69 per cent among boys and 75 per cent in girls.

During the research, the children also completed questionnaires on their mental health, physical activity habits and sleep patterns.

The study found that boys and girls who checked social-media sites more than three times a day undertook less physical activity and didn't sleep as much – but most worryingly, had poorer mental health and greater psychological distress.

Girls who used social media the most were also more likely to say they were less happy and more anxious in subsequent years.

The researchers said this was clear evidence of a "strong link between social media use and mental wellbeing".

In their conclusions, the researchers added that physical activity should be promoted as an intervention to the issue.

"Mental health harms related to very frequent social media use in girls is linked to a combination of exposure to cyberbullying, lack of physical activity and displacement of sleep," the report reads.

"Interventions to promote mental health should include efforts to ensure physical activity and adequate sleep in young people."

• To access the full report, click here for The Lancet Child & Adolescent Health.