Chronic insufficient sleep may increase overall body fat in children, according to a recent study.

Researchers from Massachusetts General Hospital found that children who consistently received less than the recommended hours of sleep during infancy and early childhood had increases in both obesity and in adiposity or overall body fat at age 7.

"Our study found convincing evidence that getting less than recommended amounts of sleep across early childhood is an independent and strong risk factor for obesity and adiposity," Elsie Taveras, lead author of the study and chief of General Pediatrics at MGHfC, said in a statement. "Contrary to some published studies, we did not find a particular 'critical period' for the influence of sleep duration on weight gain. Instead, insufficient sleep at any time in early childhood had adverse effects."

For the study, researchers analyzed data from Project Viva, a long-term investigation of the health impacts of several factors during pregnancy and after birth. Information used in this study was gathered from mothers at in-person interviews when their children were around 6 months, 3 years and 7 years old, and from questionnaires completed when the children were ages 1, 2, 4, 5 and 6.

In the questionnaires, mothers were asked how much time their children slept, both at night and during daytime naps, during an average day. Measurements taken at the seven-year visit included not only height and weight but also total body fat, abdominal fat, lean body mass, and waist and hip circumferences - measurements that may more accurately reflect cardio-metabolic health risks than BMI alone.

Curtailed sleep was defined as less than 12 hours per day from ages 6 months to 2 years, less than 10 hours per day for ages 3 and 4, and less than 9 hours per day from age 5 to 7. Based on the mothers' reports at each age, individual children were assigned a sleep score covering the entire study period - from 0, which represented the highest level of sleep curtailment, to 13, indicating no reports of insufficient sleep.

Researchers found that children with the lowest sleep scores had the highest levels of all body measurements reflecting obesity and adiposity, including abdominal fat which is considered to be particularly hazardous. The association was consistent at all ages, indicting there was no critical period for the interaction between sleep and weight. Lower sleep scores were more common in homes with lower incomes, less maternal education and among racial and ethnic minorities; but the association between sleep and obesity/adiposity was not changed by adjusting for those and other factors.

"While we need more trials to determine if improving sleep leads to reduced obesity, right now we can recommend that clinicians teach young patients and their parents ways to get a better night's sleep - including setting a consistent bedtime, limiting caffeinated beverages late in the day and cutting out high-tech distractions in the bedroom," Taveras said.  "All of these help promote good sleep habits, which also may boost alertness for school or work, improve mood and enhance the overall quality of life."

The findings were recently published in Pediatrics.