Symptoms of major depression and obstructive sleep apnea can overlap in many patients. The question that always arises is: Which comes first? Or are they two separate conditions that just happen to co-exist a lot? This interesting study looked 31 patients who had a formal depression diagnosis but were screened out for obstructive sleep apnea. Compared to healthy controls, these patients had significantly higher rates of flow limitation, which is a milder form of partial breathing obstruction that doesn’t qualify to be classified as an apnea or hypopnea. Flow limitation describes flattening of the nasal airflow tracings, which is associated with interrupted and poor quality sleep. Overall, patients with major depression were 5.86 times more likely to have a diagnosis of obstructive sleep apnea. Interestingly, all the patients that were screened out for significant obstructive sleep apnea also had a depression diagnosis.
What this paper suggests is that milder forms of sleep-related breathing disorders may contribute to symptoms of major depression. The study authors didn’t treat these patents with flow limitations, but sleep doctors will tell you that by normalizing these flow limitations, sleep quality can be significantly improved. Clinically, I see depression symptoms improve often after using CPAP or dental appliances, even if they don’t have obstructive sleep apnea but have narrowed upper airway passageways.