The data from Carpi et al in this issue of the Journal of Clinical Sleep Medicine demonstrates another possible benefit of treatment of obstructive sleep apnea (OSA) with continuous positive airway pressure (CPAP).1 Over the years, data continues to show rising negative health effects of untreated OSA, seemingly affecting everything from the skin and eyes to nearly everything internally. As these negative health effects continue to be discovered, clinicians, patients, insurance companies, and others want to know if treatment of OSA can improve these associated comorbidities.
Growing evidence shows that OSA may play a role in bone mineral density (BMD) and may be an underrecognized cause of secondary osteopenia and osteoporosis.2–5 This data is of particular concern given the high prevalence of osteoporosis and associated elevated risk of bone fractures, increased mortality, and high economic burden, costing approximately $17.9 billion per annum in the United States.6–8 A study from 2021 reported the global osteoporosis prevalence to be 23.1% of women and 11.7% of men ages 15–105 years.6 Low bone mass, a precursor to osteoporosis, affects 51.5% of women and 33.5% of men ≥ 50 years old in the United States, according to 2017–2018 data from the National Center for Health Statistics.7 This data also showed that osteoporosis prevalence increased in women, but not men, in a 10-year time span.7 The mechanism by which OSA can affect bone metabolism and structure may occur via hypoxemia, sleep fragmentation, insufficient sleep, increased sympathetic tone, alterations in hormones, and/or comorbid conditions.5
Carpi et al1 evaluated BMD and bone-related serum biomarkers in 60 male patients (age 55.1 ± 9.9 years) with severe OSA (apnea-hypopnea index ≥ 30 events/h) at baseline and after 12 months of adherence to CPAP therapy. In this study, no patients had osteoporosis, and only one patient had osteopenia at baseline. BMD significantly improved in the lumbar spine at L1 and L2 but was not statistically significant at L3, L4, and femur after Holm–Bonferroni correction for multiple comparisons. Serum vitamin D levels increased from 15.48 ± 7.03 to 20.62 ± 7.35 ng/mL (P < .001), calcium increased from 9.27 ± 0.40 to 9.55 ± 0.37 mg/mL (P < .001), and parathyroid hormone decreased from 68.69 ± 23.42 to 56.28 ± 16.67 pg/mL (P < .001). Lumbar spine BMD increase was associated with the decrease in parathyroid hormone. The authors noted that the effect sizes for the improvements in BMD were small, but larger effects occurred with the serum biomarkers. This study suggests that CPAP therapy may have a positive effect on bone metabolism in men with severe OSA, and the authors recommended screening for sleep disorders in patients with osteopenia or osteoporosis.
Limitations of the study need to be considered. A small sample size of men only with severe OSA was evaluated. With a higher and growing prevalence of osteoporosis in women, future studies should evaluate similar data in women. Since the effects of OSA on bone metabolism and structure may be related to hypoxemic burden and sleep disturbance,5 future studies on this topic should also more closely evaluate the oxygen desaturation index, percentage of sleep time with low oxygen levels, arousal index, and percentage of time spent in each sleep stage as well as average sleep duration. Several comorbidities, including diabetes, other sleep disorders, thyroid dysfunction, and heavy alcohol use, were excluded from this study, and important confounding factors such as dietary changes and physical activity were not investigated. Future studies should consider these factors. Lastly and importantly, none of the patients in this study had osteoporosis or bone fractures, raising a big question of whether these findings are clinically significant and needs to be further explored.
This article opens the question of another unexplored possible benefit of CPAP and warrants additional evaluation. This study is the first available investigating the effect of CPAP therapy on BMD. While statistically significant, we often question whether findings are clinically significant. Future research should include whether or not OSA treatment can statistically improve BMD in men and women with osteoporosis and osteopenia and reduce risk of bone fractures. If benefit is found in these populations, then comparison of the findings to current osteoporosis and osteopenia treatment would be of clinical significance. With future studies, we may be able to add improved BMD as another benefit of adequate OSA treatment.
ABBREVIATIONS
- BMD
bone mineral density
- CPAP
continuous positive airway pressure
- OSA
obstructive sleep apnea
Citation: Stahl, SM. Bone mineral density: another benefit of continuous positive airway pressure? J Clin Sleep Med. 2024;20(1):7–8.
DISCLOSURE STATEMENT
The author reports no conflicts of interest.
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