They found infants who slept less than 12 hours a day were at double the risk of being overweight by their third birthday than children sleeping longer.
“The combination of too little sleep and too much TV is associated with markedly elevated risk of obesity,” explained Dr. Elsie M. Taveras, an assistant professor of ambulatory care and prevention at Harvard Medical School and lead author of the study, published in the medical journal Archives of Pediatrics & Adolescent Medicine.
It is thought lack of sleep affects the regulation of hormones governing hunger and energy expenditure.
The US team studied 915 infants who were weighed and measured several times up to three years of age.
Mothers reported how many hours their child slept per day on average at six months, one year, and two years. Parents were also asked to report the average number of hours their children watched TV.
At the age of three years, 89 children in the study – 9% – were overweight.
Those getting fewer than 12 hours sleep were twice as likely to be overweight at the age of three.
Also, babies who watched two or more hours of television a day had a 16% increased risk of being overweight, compared to a 1% risk for babies who didn’t watch TV.
Taveras said: “Our findings lend support to childhood overweight prevention interventions that target both reduction in television viewing and ensuring adequate sleep duration.”
“The combination of low sleep and high TV might be acting independently to be a higher risk for obesity.”
In the UK, Government-backed surveys suggest around one in five children is overweight or obese by the age of five.