Too much TV time may be the biggest driver of childhood obesity, research suggests.
Scientists from the Barcelona Institute for Global Health set out to uncover the lifestyle habits that cause youngsters to carry dangerous amounts of weight.
After analysing more than 1,400 four-year-olds, they found screen time is more to blame than inactivity or processed food.
TV exposes youngsters to adverts for unhealthy food, while also taking time away from exercise and disturbing sleep.
One in 10 children aged between four and five in the UK were obese in 2016/17, NHS Digital statistics show.
In the US, nearly one in five (18.5%) two-to-19 year olds carry dangerous amounts of weight, according to the Centers for Disease Control and Prevention.
Childhood obesity has been linked to everything from high cholesterol and breathing problems to bullying and low self esteem, Public Health England reports.
It also increases the risk a youngster will be overweight in later life.
To learn more about the triggers of childhood obesity, the scientists analysed participants of the INMA Environment and Childhood Project.
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The youngsters’ parents completed a questionnaire about their activity levels, sleep, TV time, plant-based food intake and consumption of “ultra-processed” goods - like pastries and soda.
To see how this affects their health, BMI, waist circumference and blood pressure measurements were taken when the children were four and seven years old.
Results - published in the journal Pediatric Obesity - reveal the youngsters who spent the most time in front of the TV at four years old were most likely to be obese or overweight when they turned seven.
Excessive TV time also raised their risk of metabolic syndrome. This is the medical term for a combination of diabetes, high blood pressure and obesity, according to the NHS.
Other sedentary activities, like reading or puzzles, did not have the same affect.
“When children watch television, they see a huge number of advertisements for unhealthy food,” study author Dora Romaguera said.
“This may encourage them to consume these products.”
Eating processed foods was also associated with obesity, but to a lesser extent.
Watching TV may also stop us from nodding off by stimulating the mind and emitting a “glow” that delays the release of the “sleep hormone” melatonin.
“Previous studies have shown 45% of children are not sleeping the recommended number of hours per night,” study author Sílvia Fernández said.
“This is worrying because shorter sleep time tends to be associated with obesity.”
Martine Vrijheid - study author - agreed, adding: “It is well known unhealthy behaviours tend to overlap and interrelate”.
The scientists stress establishing healthy habits early may support a child’s wellbeing in later life.
“Identifying habits linked to overweight and obesity in the early stages of life can help us to define preventive strategies against other conditions, such as cardiovascular and metabolic diseases during adulthood,” lead author Dr Rowaedh Bawaked said.