For VOA Learning English,this is the Health & Lifestyle report.Getting a good night's sleep tonightcould guard children against weight gain in the future.According to a new study,putting preschoolers in bed by 8 p.m.could reduce their chances of becoming overweightor obese later in life by half.Preschoolers are children around the age of 4 or 5.The term 'obese' refers to calculations of your Body Mass Index,what doctors call BMI.They use a person's height, weight and age to assess their amount of body fat.BMIs help tell whether a person is underweight,normal, overweight or obese.The World Health Organization saysobesity can lead to serious long-term health problemslike diabetes, heart disease and stroke.Researchers from the Ohio State University's College of Public Healthhave found that young children who go to bed after 9 p.m.are twice as likely to be obese later in life.The researchers wrote their findings in The Journal of Pediatrics.The lead author of the study is Sarah Anderson.She is an associate professor of epidemiology.She studies how diseases spread and how they can be controlled.Anderson says that, for parents, the results of the studysupport the importance of creating a bedtime routine.She says that having a usual bedtime routineis something "families can do to lower their child's risk" of becoming overweight.A usual, early bedtime, Anderson adds,"is also likely to have positive benefits on behaviorand on social, emotional and cognitive development."Researchers used data from 977 children for the study.These children are part of a larger projectcalled the Study of Early Child Care and Youth Development.The project follows healthy babies born in 1991 in 10 U.S. cities.The children were 4 ? years oldwhen their mothers reported their usual weekday bedtime.Researchers then divided the children into three groups:those who went to bed by 8 p.m. or earlier,those who went to bed between 8 p.m. and 9 p.m.and those whose bedtimes were after 9 p.m.When these children turned 15 years old,the researchers looked at their rates of obesity.Of those with the earliest bedtimes,only one out of 10 was obese.Of those who went to bed between 8 and 9 p.m.,16 percent became obese.And out of those with the latest bedtimes,23 percent became obese.Anderson said putting children in bed earlydoes not mean they will immediately fall asleep.But, she adds, it makes it "more likelythat children will get the amount of sleep they need to be at their best."But Anderson says it is important to understandthat having early bedtimes may be harder for some families than others.She says that, "families have many competing demandsand there are trade-offs that get made."For example, she says, if some parents work late,that can push the children's bedtimes to later in the evening.Obesity among children in the United States is a major health concern.About 17 percent of children and teenagers in the U.S. are considered obese.That is according to the Centers for Disease Control and Prevention.The World Health Organization reported in 2014that the number of overweight babies and young children worldwidehad increased from 31 million in 1990 to 44 million in 2012.If that trend continues, the WHO warns,there will be 70 million obese children in the world by 2025.