In some areas of medicine, there is a clear trail between one health condition as it leads to another. For example, obesity is clearly linked to an increased risk of Type 2 diabetes. When it comes to sleep apnea and depression, the trail is more circular, with each condition potentially affecting the other. Here’s what you should know.

How many people with sleep apnea suffer from depression?

Sleep apnea, also referred to as sleep disordered breathing, affects approximately 25 million people in the U.S. (although the undiagnosed number is likely considerably higher). Of the three types of sleep apnea – obstructive, central, and complex – obstructive sleep apnea is the most common.

In obstructive sleep apnea, the sleeper’s throat and tongue relax so much that the airway becomes blocked. Sometimes excessive or swollen tissues of the adenoids or tonsils cause this, but in many cases common risk factors include obesity and snoring.

Regardless of the cause or type of sleep apnea, sufferers report daytime fatigue, headache or migraine, inability to concentrate, and general irritability. Sleepers also have an increased risk of cardiovascular disease and high blood pressure when they have untreated sleep apnea.

But there is another risk of untreated sleep apnea: depression. In a 2017 study, over 50% of depressed patients had an abnormal polysomnograph that indicated severe obstructive sleep apnea, with almost 100% of patients exhibiting some level of sleep apnea.

Even with this connection, it remains challenging to pinpoint exactly how many people suffer from sleep apnea and clinical depression. A review of literature put the estimated range of those suffering from sleep apnea and depression from five to 63%, which is so broad as to be almost unhelpful. Even though it is clear from the review that there’s a link between depression and sleep apnea, correlation does not equal causation, making it hard to find exact statistics of prevalence.

Why are sleep apnea and depression associated?

Still, researchers remain convinced that there’s a link between sleep apnea and depression (and sleep apnea and anxiety). There may be different connections, but the link is there. Here’s what we do know.

Poor sleep can trigger depression and anxiety

One study indicated that not only does poor sleep seem to trigger depression but it also increases the chances of clinically significant depression and anxiety. Another demonstrated the correlation between poor sleep and increased anxiety, even when controlling for other factors. The severity of the anxiety was also directly correlated with the severity of the sleep apnea – the more severe the sleep apnea, the higher the anxiety level.

Another larger study by the Centers for Disease Control and Prevention confirmed these results: the more frequent pauses in breath (apneas), the more severe the depression.

The role of inflammation in sleep apnea and depression

It has been well-documented that individuals with depression have higher levels of inflammation overall than those without it. While this excess inflammation in depressed people is modest, literature reviews have found that it can have profound effects on depression levels.

For people with sleep apnea, study findings are mixed. Certainly, obese patients with sleep apnea have increased inflammation in their body, and weight loss can address both the inflammation and sleep apnea concurrently. While researchers know the connection between inflammation and sleep apnea exists, each study recommends more research to confirm.

Sleep apnea or depression? A complicated diagnosis

What further complicates the relationship between sleep apnea and depression is that sleep apnea is often misdiagnosed as depression. One of the major symptoms of both disorders is daytime sleepiness or extreme fatigue. Because of this, patients may be diagnosed with depressive disorders and treated as such. If sleep apnea is the true diagnosis, patients will not see much improvement in symptoms, which can trigger worsening depression.

The physical mechanisms that connect sleep apnea and depression are also