DEAR DOCTOR K: I recently saw a headline that said children who sleep less weigh more. Is that true? How much sleep should my preschooler and first-grader get each night?
DEAR READER: I believe you’re referring to a study recently published in the medical journal Pediatrics. Researchers found that children who don’t get enough sleep may also have a higher risk of being overweight.
Researchers from Harvard-affiliated Massachusetts General Hospital for Children kept track of more than 1,000 children from the ages of 6 months to 7 years. They asked mothers how much sleep their children got at the age of 6 months, 1 year, and then every year until the end of the study.
Between ages 7 and 8, researchers measured the children’s body fat and body mass index (BMI). They found that kids who were the most sleep-deprived were about 2 1/2 times as likely to be obese as those who consistently got enough sleep. They also scored higher on other measurements of body fat.
This study further confirms a link between sleep and weight. Many previous studies have also shown that when children and adults don’t get enough sleep, it increases their risk of being overweight and having heart disease.
How much sleep should your children get? These are the recommended daily amounts for young kids:
— 6 months to 2 years: 12 hours
— 3 to 4 years: 10 hours
— 5 to 7 years: 9 hours
Here are some ideas for improving the amount and quality of your child’s sleep:
— Set and enforce a regular bedtime.
— Limit TV, especially before bedtime. The kind of light emitted by a TV can make it harder to fall asleep.
— Have soothing bedtime routines, such as bathing, quiet time and reading stories.
— Consider room-darkening curtains or a white-noise machine.
Why would sleeping less increase a child’s (or an adult’s) weight? We don’t know for sure that it does. But in recent years we’ve discovered some ways that it could. Most of the studies have been done with adults, not kids. In adults, experiments that restrict sleep to four to five hours each night lead to a fall in blood levels of the hormone leptin.
Leptin travels in the blood, reaches the brain and has two effects. First, it decreases appetite. Second, it speeds up metabolism, which leads the body to burn more calories. So lower-than-normal levels of leptin would increase appetite and cause the body to burn fewer calories.
Restricting sleep increases blood levels of another hormone, ghrelin. This hormone is made in the stomach. When it reaches the brain, it increases appetite — particularly an appetite for high-calorie foods.
Low blood levels of leptin and high blood levels of ghrelin are a kind of double whammy: They cause a person to consume more calories, and burn those calories less efficiently.
Of course, sleep isn’t the only factor when it comes to childhood obesity. Along with making sure your children get enough sleep, make sure they are active for at least an hour a day. Limit sweetened drinks, and feed them a healthy diet with plenty of fruits and vegetables.
Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.