Obesity and Respiratory Diseases

Dr. Terence TAM - Honorary Treasurer, HKOS

Patient with obstructive sleep apnea (OSA) are at increased risk for poor neurocognitive performance and adverse medical outcomes due to repeated arousals and/or hypoxemia during sleep over months to years, and severe untreated OSA has been associated with increased all-cause and cardiovascular mortality. In both males and females, the strongest risk factor for OSA is obesity. The prevalence of OSA progressively increases as the body mass index (BMI) and associated markers (e.g., neck circumference, waist-to-hip ratio) increase. The strong association between OSA and obesity has implications for the overall burden of OSA in populations with rising levels of obesity. In adult males, the estimated prevalence of OSA (defined as an AHI ≥5 plus daytime sleepiness) rose from 11 to 14 percent over the span of two decades; in adult females the prevalence rose from 4 to 5 percent. Obesity, particularly when severe, is also a risk factor for concomitant obesity hypoventilation syndrome (OHS), a condition which is defined as the presence of awake alveolar hypoventilation (raised PaCO2) in an obese individual which cannot be attributed to other conditions, such as pulmonary parenchymal disease, skeletal restriction, neuromuscular weakness, hypothyroidism, or pleural pathology. Individuals with OHS have considerably worse health status and access more health care resources compared to the general population, with differences apparent up to eight years before a diagnosis is made.

While it is easier to appreciate the link between obesity and sleep apnea, the general medical community is often taken by surprise on the relationship between obesity to other respiratory diseases. Cross-sectional and longitudinal studies have linked obesity with asthma, and obese patients with asthma are known to suffer from more acute attacks, increased use of asthma medication, frequent visits to the emergency department (ED), and more hospital admissions than their non-obese counterparts. Chronic Obstructive Pulmonology Disease (COPD) and obesity also share a complex interplay of similarities, which seems to compound each condition. Both are associated with deterioration in lung function, hypoxia, and a low-grade systemic inflammation, which predispose to increasing medical morbidity and mortality. Physiological and metabolic factors related to COPD and obesity seems to jeopardize morbidity and mortality further when in association.

The list is not meant to be exhaustive, but only to highlight the interaction between obesity and the respiratory system, and underpin the importance of treating obesity in order to ameliorate a multitude of respiratory conditions.