Three-year-old children who watch more than eight hours of TV a week are at a higher risk of obesity, a study says.
Watching TV was one of eight obesity-risk factors identified
TV watching was one of eight factors, including lack of sleep and parental obesity, linked to an increased risk of weight problems in young children.
University of Glasgow and Bristol researchers said the findings supported the theory that early life environment could determine obesity.
The study of 9,000 children appeared in the British Medical Journal.
Child obesity levels have shot up in recent years.
Among two to four-year-olds obesity has doubled since the early 1990s, while the rate has trebled for six to 15-year-olds.
The eight key factors identified by the researchers were:
- Birth weight
- Parental obesity
- Over eight hours of TV a week at age three
- Short sleep duration - less than 10.5 hours per night at age three
- Size in early life - measured at eight and 18 months
- Rapid weight gain in the first year of life
- Rapid catch-up growth up to two years of age
- Early development of body fatness in pre-school years - before the age at which body fat should be increasing.
Researchers said the way these factors might increase risk were complex.
Parental obesity, for example, may increase the risk through genetics, or by shared family experience, such as food intake.
And TV watching at aged three - although the risk could easily apply to other ages in the early years - could have an effect either through lack of exercise, or eating more.
Children who slept longer were likely to be more physically active, they added.
The authors said a lot of interventions to prevent obesity had been unsuccessful so far.
But they added: "Future interventions might focus on environment changes targeted at relatively short periods in early life, attempting to modify factors during pregnancy, in infancy, or in early childhood, which are independently related to later risk of obesity."
Professor Tony Barnett, head of the University of Birmingham's diabetes and obesity group, said the findings were not unexpected.
"There are some genetic factors which play a role, but the basic message is that it is the environment," he said.
"The rise in obesity we have seen in recent years cannot be down to genes."
And Dr Ian Campbell, president of the National Obesity Forum, added: "What we have got to convince parents is that environmental factors are important to make sure their children do not become obese.
"They must stop them watching TV and playing computer games all the time - these lifestyle factors are key."