Janice F. Bell of the University of Washington in Seattle, and Frederick J. Zimmerman of the University of California, Los Angeles write that the results, suggest that there is a critical window prior to age 5 years when nighttime sleep may be important for subsequent obesity status. They added, Sleep duration is a modifiable risk factor with potentially important implications for obesity prevention and treatmentInsufficient nighttime sleep among infants and preschool-aged children appears to be a lasting risk factor for subsequent obesity, while contemporaneous sleep appears to be important to weight status in adolescents. Napping had no effects on the development of obesity and is not a substitute for sufficient nighttime sleep. The actual reason behind this phenomenon is not precisely known, but the authors of the study said that getting less sleep could lead to decreased physical activity due to tiredness and increased energy intake because the waking child has more opportunities to eat.