The interaction between obesity and OSA is complex. Although it is often assumed that obesity is the major cause of OSA, and that treatment of the OSA might mitigate further weight gain, new evidence is emerging that suggests this may not be the case. Obesity explains about 60% of the variance of the apnea-hypopnea index (AHI) definition of OSA, mainly in those < 50 years and less so in the elderly. Moreover, long-term treatment of OSA with CPAP is associated with a small but significant weight gain. This weight gain effect may result from abolition of the increased work of breathing associated with OSA. This suggests complex two-way interactions between obesity, OSA, and age. It’s plausible that in younger individuals, obesity is a primary driver of OSA, while in older individuals, other factors become more significant contributors to OSA severity. The observation that CPAP therapy can lead to weight gain raises further questions about the metabolic consequences of OSA treatment.
It is possible that the increased energy expenditure due to labored breathing during apneic events contributes to a negative energy balance in untreated OSA. Correction of OSA with CPAP may then reduce this energy expenditure, leading to a positive energy balance and subsequent weight gain. Furthermore, the improvements in sleep quality and reduction in daytime sleepiness associated with CPAP might also influence appetite and physical activity levels, further contributing to weight gain. Future research should focus on elucidating the mechanisms underlying the complex relationships between obesity, OSA, age, and the metabolic effects of OSA treatment. This will be crucial for developing more targeted and effective strategies for managing both conditions.
Unfortunately, weight loss by either medical or surgical techniques, which often cures type 2 diabetes, has a beneficial effect on sleep apnea in only a minority of patients. A short jaw length may be predictive of a better outcome. Slight fall in the overall AHI with weight loss, however, may be associated with a larger drop in non supine AHI, thus converting some patients from non positional to positional (ie, supine only) OSA. Patients with moderate to severe obesity-related OSA, the combination of weight loss with CPAP appears more beneficial than either treatment in isolation.