The Association Between Chronotype and Weight Change Among Medical Students: A Cross-Sectional Study.

Abstract

Purpose: This study analyzed the differences in weight change among medical students with different chronotypes and evaluated the association between chronotype and weight change after controlling for confounders.

Methods: Using proportional stratified cluster random sampling, 1300 medical students (excluding freshmen) were selected from April to September 2021. Chronotype was assessed with the Chinese version of MEQ-5 questionnaire, categorized into five groups: definite morning, moderate morning, intermediate, moderate evening, and definite evening. The primary outcome was weight change value (kg), the difference between current weight and weight at admission; the secondary outcome was weight gain (≥10% increase from admission weight). Multiple linear and logistic regression models were used to analyze the independent association between chronotype, weight change value, and weight gain, respectively.

Results: Among the 1300 medical students, the proportion of definite morning, moderate morning, intermediate, moderate evening, and definite evening chronotype were 14.08%, 12.38%, 28.92%, 31.46%, 13.15%, respectively. Definite evening-type students had worse sleep quality, shorter sleep duration, more late-night snacks, higher satiety, and lower breakfast frequency (P<0.05). Compared to definite morning-type medical students, those with moderate morning, intermediate, moderate evening and definite evening chronotype showed an increasing trend of weight change (P=0.044), with definite evening-type students gaining 0.88 kg on average (95% CI: 0.10, 1.65), consistent after adjusting for confounders. The association between chronotype and weight gain was similar although not statistically significant (OR=1.96, 95% CI: 0.72, 5.36). Evening chronotype with dinner ≥ 6 PM had the highest odds of weight gain compared to morning chronotype with dinner before 6 PM (OR=2.43, 95% CI: 1.07, 5.50).

Conclusion: Definite evening chronotype was associated with greater weight increase and higher odds of weight gain among medical students, especially when dinner ≥ 6 PM. These findings highlight the importance of morning chronotype and early dinner for weight control.