Association between chronotype and body mass index: The role of C-reactive protein and the cortisol response to stress.
Level 4 - case-series / case-control
Cross-sectional laboratory observational study with mediation analysis
PubMed 31398588 · doi:10.1016/j.psyneuen.2019.104388
What was done
Twenty-eight healthy young adults (mean age 23.8 ± 3.3 years; 50% women) completed the Morningness-Eveningness Questionnaire (MEQ) to determine chronotype and underwent the Trier Social Stress Test (TSST). Baseline plasma C-reactive protein (CRP) and pre- and post-stress salivary cortisol concentrations were assessed alongside continuous heart rate monitoring. The authors evaluated correlations among MEQ score, body mass index (BMI), CRP, and cortisol reactivity, and tested CRP as a mediator and cortisol reactivity as a moderator of the chronotype-BMI relationship.
What was found
Evening tendency (lower MEQ score) was significantly correlated with higher BMI (r = -0.40, p < 0.05), higher baseline CRP (r = -0.42, p < 0.05), and greater cortisol response to stress (r = -0.53, p < 0.01). Baseline CRP significantly mediated the relationship between MEQ score and BMI (b = -0.03, 95% CI: -0.08 to -0.007, p < 0.05). Cortisol reactivity moderated this mediated pathway (b = 0.005, 95% CI: 0.0002 to 0.01, p < 0.05), with the mediated effect being stronger in individuals exhibiting higher cortisol responses.
Why it matters
These findings suggest that systemic low-grade inflammation and heightened neuroendocrine stress reactivity may be biological pathways linking evening chronotype to elevated obesity risk.
Limits
The sample size is very small (n = 28), making complex mediation and moderation analyses prone to overfitting and type I errors. The cross-sectional design cannot establish causality or directionality. The study was limited to healthy young adults, restricting generalizability to older or metabolically impaired populations.
Cited by
- supports Evening chronotypes who do not sleep according to their circadian preference have higher C-reactive protein, poorer HbA1c control, and higher obesity rates.