Social jetlag (SJL), a misalignment between circadian rhythms and social schedules, is associated with obesity susceptibility. This cross-sectional study investigated how a metabolic-genetic risk score (GRS), based on Fat Mass and Obesity Associated (FTO), Melanocortin 4 Receptor (MC4R), and Transcription Factor 7-Like 2 (TCF7L2) genes, influences the relationship of SJL and obesity‑related traits in 223 adults (24-50 y) recruited from an outpatient clinic in Ankara, Turkiye. Anthropometric, clinical, and biochemical data were collected. Blood-derived DNA was genotyped using real-time PCR.SJL was calculated as the difference between weekday and free-day sleep midpoint, and sleep quality was assessed with Pittsburgh Sleep Quality Index. Participants with SJL had significantly higher Body Mass Index (BMI), waist and hip circumference, body fat mass (BFM), and insulin levels (p < 0.05). Although SJL was associated with higher BMI (26.1 ± 4.52; 24.9 ± 4.20 kg/m2, p = 0.004), this association was attenuated after adjustment for metabolic-GRS (p = 0.062). Individuals carrying > 2 risk alleles had higher BMI than those with ≤2 alleles (p = 0.036). Among participants with SJL, metabolic-GRS was positively associated with BMI (p = 0.005), BFM (p = 0.047), and visceral fat percentage (p = 0.046). In conclusion, SJL may interact with genetic susceptibility for obesity, emphasizing the importance of regular sleep patterns in combating obesity.
