Formula for Calculating Optimal Sleep Duration in Adolescents

A recently proposed formula for estimating optimal sleep duration (OSD) incorporates social jetlag and standardized body mass index (BMI), both of which are challenging to measure accurately. In the current study, a formula using not standardized BMI but actual BMI to estimate OSD was proposed. Among 2,540 students in grades 5 to 11, "ideal" students were identified as those reporting no daytime sleepiness and having a standardized BMI within ±1.5. Their habitual sleep duration was regarded as their "assumed OSD." "Non-ideal" students were classified based on their reported sleepiness during class (on a scale from 1 = never to 4 = always) and their standardized BMI [high (≥1.5), medium (within ±1.5), and low (≤-1.5)]. The difference in average sleep duration between the ideal and non-ideal groups was added to each non-ideal student's habitual sleep duration to calculate their "assumed OSD." Multiple regression analysis was conducted using bedtime (on schooldays and non-schooldays), wake time (on schooldays and non-schooldays), BMI, grade, gender, self-reported academic performance, after-school activity (hours/week), breakfast frequency score, defecation frequency score, physical activity (days/week), and screen time (on schooldays and non-schooldays) as independent variables, with "assumed OSD" as the dependent variable. A significant linear formula for estimating OSD was derived: 23.375 - 0.710 * (bedtime before schooldays) - 0.286 * (bedtime before non-schooldays) + 0.714 * (wake time on schooldays) + 0.281 * (wake time on non-schooldays) + 0.513 * (sleepiness score; 1-4) + 0.009 * [gender (male: 1; female: 2)] + 0.003 * (BMI). A straightforward formula for estimating individual OSD was proposed, although further research is required for validation.