**Background:** Shift workers, particularly night workers, are susceptible to sensorimotor, metabolic, and endocrine disorders due to sleep debt and circadian desynchronization. Overweight and obesity are prevalent among shift workers and are associated with structural body changes that impair postural stability, increasing fall risk. Female night workers may be especially vulnerable due to gynoid fat distribution patterns. This study aimed to investigate relationships between sleep duration (TST) and postural control in female night workers before and after shift, and to determine whether BMI influences postural control in this population.
**Methods:** This cross-sectional study recruited 36 female night workers from a Brazilian philanthropic company in São Paulo; 14 met inclusion criteria after exclusions (8 unable to complete evaluations, 7 worked double shifts, 2 napped during night work, 5 had sleep complaints). Participants were PSG technicians who had worked ≥1 year on a fixed 12-hour night shift/36-hours off schedule. Evaluations occurred over 7 days: actigraphy (Sleepwatch, nondominant wrist) and sleep diaries were used for 7 days; body mass and height were measured on day 1; postural control was assessed on day 6 (pre-shift, 19:00-19:50) and day 7 (post-shift, 08:10-09:00) using an OR6 AMTI force platform. Participants stood in bipedal support for 30 seconds under eyes-open and eyes-closed conditions (two trials each). CoP parameters (Vel_ap, Vel_ml, Vel_total, Cpath_ap, Cpath_ml) were calculated. Statistical analysis used paired t-tests, Pearson correlations, and linear regression (stepwise method) with significance at p<0.05.
**Key Results:** Participants were sedentary, overweight women (mean BMI 27.4 ± 2.8 kg/m², mean age 35.0 ± 7.7 years). Mean TST before night work was 259.9 ± 67.5 minutes (4 hours 33 minutes); sleep efficiency was 98.3 ± 1.4%. Postural control parameters showed no significant differences between pre- and post-shift measurements (all p>0.05). However, positive correlations were found between BMI and postural control parameters in the anteroposterior direction under both eyes-open and eyes-closed conditions, before and after shift. For eyes-open pre-shift: Vel_ap (r=0.593, p=0.025), Vel_total (r=0.543, p=0.045), Cpath_ap (r=0.593, p=0.025). For eyes-open post-shift: Vel_ap (r=0.764, p=0.001), Vel_total (r=0.678, p=0.008), Cpath_ap (r=0.764, p=0.001). For eyes-closed pre-shift: Vel_ap (r=0.660, p=0.010), Vel_total (r=0.613, p=0.020), Cpath_ap (r=0.660, p=0.010). For eyes-closed post-shift: Vel_ap (r=0.648, p=0.012), Vel_total (r=0.536, p=0.048), Cpath_ap (r=0.648, p=0.012). No correlations were found between TST and any postural control parameter, nor between BMI and mediolateral direction parameters. Linear regression showed BMI significantly predicted postural sway: before shift eyes-opened R²=0.352 for Vel_ap and Cpath_ap (β=0.05, 95%CI 0.01-0.10, t=2.55; β=1.62, 95%CI 0.24-3.00, t=2.55); after shift eyes-opened R²=0.583 for Vel_ap and Cpath_ap (β=0.07, 95%CI 0.03-0.10, t=4.10; β=2.12, 95%CI 0.99-3.24, t=4.10).
**Clinical Implications:** This study demonstrates that higher BMI is significantly associated with increased anteroposterior postural sway in female night workers, independent of sleep duration or visual input. The mean TST of <5 hours represents substantial sleep deprivation, yet sleep duration did not correlate with postural control. The findings suggest that overweight/obesity may be a more important risk factor for postural instability and fall risk in night workers than acute sleep deprivation alone. The anteroposterior direction was predominantly affected, consistent with theories that abdominal fat distribution anteriorizes the center of mass. The lack of mediolateral associations may reflect compensatory widening of the support base in women with lower-body fat distribution. Limitations include small sample size (n=14, 76% power), lack of control group, all-female sample, and absence of lower limb strength and sensory measurements. Despite non-significant pre-post shift differences, the observed 3.3-4.0% increases in anteroposterior sway parameters post-shift under eyes-open conditions may have practical safety implications. These results support implementing workplace interventions targeting weight management and postural assessment for female night workers to reduce occupational fall and injury risk.