Teaching parents how to improve their baby's sleep appears to roughly halve the rate of childhood obesity, but the authors of a new University of Otago study are not sure why.
Study co-leader Prof Barry Taylor said the sleep lessons appeared to have cut the obesity rate by 50 per cent but they did not improve sleep duration or quality.
Taylor said parents were told not to sing to babies or carry them around when trying to get them to sleep. Instead they were told to put them down in a quiet, reasonably dark place.
"What you are trying to do is to teach them to self-regulate, to teach them how to go to sleep by themselves."
It was possible the self-regulation inherent in learning to sleep without parental stimulation meant infants were less likely to overeat.
"We think it works through some kind of subtle parenting change ... in the end we actually want babies and young children to listen to their body and eat when they're hungry."
Sleep lessons made no difference to the duration or quality of the sleep.
The study involved 802 Dunedin families split into groups that received different levels of help and advice.
One group received additional support around food, exercise, and breast-feeding; another group received the sleep programme, and some families received all of the interventions.
The extra advice around food, activity, and breast-feeding resulted in no change in obesity levels, which surprised the researchers.
The study co-leader was Prof Rachael Taylor, the director of the Edgar Diabetes and Obesity research centre.
Families in the sleep group had one class before the baby was born, and a personal visit from a sleep nurse when their baby was three weeks old. Some families requested extra help if their baby still had difficulties sleeping after six months of age.
The two-year Prevention of Obesity in Infancy study has been published in the journal Pediatrics.