Impact of the Visceral Adipose Tissue on Bone Quality in Patients with Untreated mild-to-severe Obstructive Sleep Apnoea

Obstructive sleep apnea (OSA) is an increasingly prevalent sleep disorder characterised by upper airway obstruction during sleep, resulting in breathing pauses, intermittent hypoxia, and fragmented sleep. The strongest risk factor for OSA is obesity, in particular visceral obesity. The risk of OSA progressively rises with increases in BMI (body mass index). In a population-based study of more than 1,000 subjects, OSA (defined by an apnea-hypopnea index-AHI ≥ 15) was present in 11% of men having a normal BMI, in 21% of those having a BMI between 25 and 30 kg/m2 and in 63% of those who were obese (BMI >30 kg/m2). The same trend was observed in women. As a result of this association, the highest rate of OSA is found in countries with a high prevalence of obesity, and due to the increasing levels of obesity, the prevalence of OSA is also on the increase. Many comorbidities are associated with obesity, such as insulin resistance, elevated blood pressure, and metabolic syndrome, but little is known about the relationship between fat distribution and bone impairment in these patients. For this reason, we aimed to evaluate the impact of the visceral adipose tissue (VAT) on the bone quality of OSA patients. In our prospective study, we selected forty-nine patients with untreated mild-to-severe OSA who underwent polygraphy in our dedicated ambulatory for sleep disease. All subjects performed a dual-energy X-ray absorptiometry to evaluate body composition and bone status. Anamnestic and clinical information and data from the instrumental tests performed were collected. According to the recent reference values for European adults, patients were divided by the sex-related threshold of the VAT index into two categories: VAT index within limits (normal VAT, nVAT) and increased (iVAT). 63% of patients were iVAT. Compared with nVAT, iVAT patients had a higher prevalence of arterial hypertension (52% vs 22%), diabetes (32% vs 6%) and higher values of mean nocturnal desaturation. We found that patients with iVAT had, in comparison to nVAT, lower values of the lumbar spine trabecular bone score (TBS) (mean 1.24 vs 1.39; p<0.001), TBS T-score (mean -1.82 vs -0.52; p<0.001) and TBS Z-score (mean -0.35 vs 0.75; p=0.002). Moreover, a close association was present between the VAT index and TBS lumbar spine L1-L4 (r2 linear 0.573; p<0.001) and altered values of the TBS Z-score were associated with the severity of vertebral fractures. Finally, in a linear regression-adjusted model, the VAT index predicted TBS lumbar spine L1-L4 (β -0.323; p<0.001). In conclusion, VAT impacts bone quality in OSA patients, particularly on trabecular bone microarchitecture. In these patients, the role of VAT as a metabolically active tissue should be considered and quantified: studying the body composition is important to research or prevent osteopenia, osteoporosis, or osteoporotic fracture.