The influence of chronotype on the body mass index of U.S. college students.

Objectives: The relationship between a college student's chronotype and body mass index (BMI) is important to understand for university decision makers who want to build healthy and inclusive academic communities. This study aimed to evaluate how a student's chronotype influences their BMI.

Material And Methods: Participants were college students from Oral Roberts University (n=384) with a mean age of 18.94 years, a mean BMI of 24.7kg/m, and a mean morningness-eveningness questionnaire (MEQ) score of 47.65.

Results: BMI values were significantly correlated with both chronotype (r=-.11, β=-.09, p=.03) and age (r=.12, β=.53, p=.02). The rate at which BMI increased with age depended upon the student's chronotype (β=.81-.005 / MEQ, p=.005). The later the chronotype, the higher the rate of increase. Race had no significant influence on MEQ or BMI values except in the case of students who identified as Black and female. These students were found, on average, to have significantly higher BMI values (p<.01).

Conclusion: For college students, BMI tends to increase over time and at a rate that is dependent upon chronotype. The later the chronotype, the faster the rate at which BMI increases. BMI values were found to be significantly higher for Black females. However, this result is potentially spurious, as BMI does not take into account differences in body composition between genders and race/ethnicity groups.