New research indicates that children who spend less time sleeping are more likely to be overweight - even obese - as adults.
The University of Otago followed the development of more than 1,000 children born in Dunedin between 1972 and 1973.
The study has been published in the United States journal Paediatrics.
It shows children between 5-years-old and 11-years-old who spent less time in bed had a higher Body Mass Index and were more likely to be obese when got older.
It suggests that tired children may have less energy and therefore tend to be less active.
Lead author of the study Erik Landhuis says it may be hormone related.
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