Infants and preschool toddlers who have difficulty in getting enough sleep at night have a higher risk of developing obesity later in childhood years. The researchers also found that the daytime sleep is not a good enough substitute for lost nighttime sleep in terms of preventing obesity.

The study involved observing 1,930 children from the US, ages 1 month to 13 years, who were divided into two groups. Half of them were younger (ages 1 month to 59 months) and older (ages 5 to 13 years).

Data on the children was collected at the beginning of the study in 1997 and repeated in the year 2002.

In the group of younger children, lack of sufficient nighttime sleep at baseline was linked with increased risk for later overweight or obesity. Among the older children, the number of sleeping hours at baseline was not related with weight at follow-up.

Janice F. Bell of the University of Washington in Seattle, and Frederick J. Zimmerman of the University of California, Los Angeles wrote, “Findings suggest that there is a critical window prior to age 5 years when nighttime sleep may be important for subsequent obesity status.”