PROJECT SUMMARY Preventing overweight in preschoolers may be an effective way to reduce the lifetime risk of obesity. Though adequate, quality sleep is increasingly recognized as essential for maintaining a healthy weight, the risk factors for insufficient sleep in preschoolers are poorly understood. While media use has been associated with insufficient sleep in preschoolers, most studies are limited because of unmeasured confounding related to household chaos and a sole focus on total media use quantity or bedroom media use without considering media content. Furthermore, insufficient sleep likely leads to overeating in adults, yet few studies have considered that effect in preschoolers. My long term goals are to become an expert in how preschoolers engage with media and how media use impacts sleep and obesity risk, while emphasizing the use of wearable devices to objectively measure media use and sleep. My objectives for this mentored research scientist development award are thus to become an expert in 1) conducting prospective research studies on obesity prevention in early childhood, 2) media use behaviors in preschoolers, 3) using wearable devices to objectively measure media use and sleep in preschoolers, and 4) mastering advanced statistical methodology needed for establishing causal inference in health behavior research. I will complete my training with coursework, participation in the plenary sessions, workshops and short-courses at targeted scientific meetings, and through the completion of a novel, prospective research study to examine the causal relationships between media use, sleep, overeating and weight gain in preschoolers. My research is particularly novel because I consider how the content of media preschoolers engage with modifies the relationship between media use and sleep. My innovative research design accounts for household chaos with a validated measure, includes the novel application of a valid, wearable audio recording device to objectively measure media exposure, and includes a laboratory-based assessment of overeating (i.e., eating in the absence of hunger) to define the association of nighttime sleep on subsequent overeating. Importantly, my program will be conducted under the guidance of an expert mentorship team that consists of a pediatrician and behavioral epidemiologist (Dr. Sargent), an epidemiologist in early child health (Dr. Karagas), a behavioral researcher in early childhood obesity prevention (Dr. Benjamin Neelon), and a statistician in behavioral research (Dr. O’Malley), as well as three advisors with specialized training in sleep and child eating behaviors. In Year 5 I will submit an R01 proposal for a prospective study properly powered to define the causal relationships between media use and excess weight gain while considering mediating...