In addition, high levels of television viewing combined with less sleep elevates the risk, so that children who sleep less than 12 hours and who view two or more hours of television per day have a 16 percent chance of becoming overweight by age 3.

Mounting research suggests that decreased sleep time may be more hazardous to our health than we imagined, says Elsie Taveras, MD, assistant professor in Harvard Medical School's Department of Ambulatory Care and Prevention and lead author on the study. We are now learning that those hazardous effects are true even for young infants.

Results are published in the April 2008 issue of Archives of Pediatric and Adolescent Medicine.

The study team identified 915 mother-infant pairs from Project Viva, a long-term study of the effects of diet and other lifestyle factors on maternal and child health over time. Infant weight and measurements were taken at several in-person visits up to three years of age. Mothers reported how many hours their child slept per day on average at 6 months, 1 year, and 2 years postpartum. Parents were also asked to report the average number of hours their children watched television on weekdays and weekends.

The combination of low levels of sleep and high levels of television viewing appeared to be synergistic and was associated with markedly higher BMI scores and increased odds of becoming overweight.

Although previous studies have shown a similar link between sleep restriction and overweight in older children, adolescents, and adults, this the first study to examine the connection in very young children, says Matthew Gillman, MD, SM, Harvard Medical School associate professor and director of the Obesity Prevention Program in the Department of Ambulatory Care and Prevention. Gillman is also the study's senior author.

Television viewing is also a known risk factor for children becoming overweight.

These study results support efforts to reduce television viewing and to promote adequate sleep in efforts to prevent and reduce unhealthy childhood weight-gain. Children who are overweight are often at higher risk for obesity and related conditions, such as hyperlipidemia, hypertension, asthma, and type II diabetes, later in life.

Getting enough sleep is becoming more and more difficult with TV, Internet, and video games in the rooms where children sleep, says Dr. Taveras. Our findings suggest that parents may wish to employ proven sleep hygiene techniques, such as removing TV from children's bedrooms, to improve sleep quality and perhaps sleep duration.

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