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October 2, 2025

Acute Effect of Continuous Positive Airway Pressure (CPAP) on Weight in Patients with Obstructive Sleep Apnea: A Randomized Study

GLGiovanni F. de LimaHospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo SHSara HerculanoHospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo MFMariana D. FernandesEscola Bahiana de Medicina e Saúde Pública

Key Points

CPAP significantly increased body weight by 0.37 kg compared to the Control group, highlighting its impact on weight.
In the CPAP group, urinary volume decreased significantly from 825 mL to 556 mL after treatment, suggesting changes in fluid management.
The study utilized a randomized design with polysomnography to assess patients with severe obstructive sleep apnea over two nights.
These findings may indicate that fluid accumulation is a key factor in weight gain experienced during CPAP therapy.

Abstract

RATIONALE: Continuous positive airway pressure (CPAP) may lead to weight gain in patients with obstructive sleep apnea (OSA), but the mechanisms are still unclear. OBJECTIVES: To investigate the effects of the first night of CPAP therapy on body weight and nocturnal urine output in treatment-naïve patients with severe OSA. METHODS: The study was conducted during 2 consecutive nights. During the first night, a baseline polysomnography (PSG) was performed. Weight, urinary parameters, and body composition change during baseline PSG were compared to the second PSG, which was randomized to either CPAP titration or repeat PSG without any intervention (Control group). Body weight and bioelectric impedance were assessed in the evening before bedtime and in the morning, after voiding. Overnight urinary volume and osmolality, antidiuretic hormone, type-B natriuretic peptide (BNP) were determined in the morning after each PSG. RESULTS: Thirty-eight patients (60% men; aged 54±9 years; body mass index: 35.0±6.2 kg/m2; apnea-hypopnea index: 71±25 events/h) completed the study (n=19 per group). CPAP led to a significant increase in body weight (0.37±0.55 Kg) compared to the Control group (-0.30±0.46 Kg), P0.999) but reduced significantly in the CPAP group from 825±389 to 556±334 mL, respectively, P<0.001. Urinary osmolality remained stable between Visits 1 (575±221 mOsm/kg) and 2 (523±225 mOsm/kg) (P=0.756) in the Control group but increased in the CPAP group from 629±183 to 746±154mOsm/kg, respectively, P=0.005. While total body water reduced overnight in the Control group, CPAP significantly attenuated the overnight reduction in total body water (P<0.001). No significant changes in antidiuretic hormone and BNP were observed. CONCLUSION: CPAP led to weight gain and fluid accumulation after a single night. These findings provide strong evidence that fluid accumulation is involved in weight gain associated with OSA treatment with CPAP. TRIAL REGISTRATION: ClinicalTrials.gov; No.: NCT05253963; URL: www.clinicaltrials.gov Key words: Body Composition; Bioelectrical Impedance Analysis; Diuresis.

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