As we reported recently, a study published in the Journal of Clinical Sleep Medicine has found that sleep apnea may be a major cause for depression, meaning that many cases of severe clinical depression could be solved with a simple continuous positive airway pressure system (CPAP) — but just why is sleep so intricately related to depression?

The findings are good news for many depression sufferers, as depression is tough to treat but sleep apnea has many established treatments, including a CPAP mask that keeps the airways open and ensures a restful sleep.

While feeling sad every now and then is just part of life, depression sufferers experience something profoundly different: tremendous fatigue, a lack of interest in anything, and a fundamental hopelessness that becomes debilitating.

Unlike most feelings of sadness which fade, depression is a persistent sadness that is often accompanied by anxiety and general hopelessness about life and disinterest in things that the person once enjoyed.

And it’s not an uncommon ailment either: an estimated 20 million Americans suffer from it, according to the National Sleep Foundation.

One thing that has been mysterious about depression is its cause, and also its solution. The pharmaceutical industry makes huge profits off selling antidepressants, many of questionable efficacy. Some may appear to help depression sufferers, but some don’t seem to benefit at all. And even the best only manage depression rather than cure it.

That’s why this recent study on sleep apnea is so important: it indicates that there may be a strong relationship between sleep and depression. In fact, there seems to be a cyclical relationship between the two, as depression can often interfere with consistent, restful sleep while lack of sleep can enhance depressive disorders. Also, some people don’t have a problem with sleep until they come down with depression, but for others, it was the sleep problems that came first.

Previous studies have already shown that sleep problems are often related to severe depressive illness, but their relationship was still largely theoretical — why was sleep so closely linked with depression, and what can be done to stop it?

Insomnia is a very common symptom in patients who suffer from depression, with studies indicate that there is a ten-fold risk that those with insomnia have for depression compared to sound sleepers.

Obstructive sleep apnea has been linked to depression in the past. There was a study of 18,980 people in Europe that was conducted by researchers at Stanford University back in 2003 that indicated that depression sufferers were five times more likely to suffer from a sleep disorder, with OSA being the most common problem, and the a CPAP machine could solve this. A 2007 study of OSA patients that used a CPAP machine for a year showed improvement in depression. This most recent study confirms what many are starting to realize: sleep apnea may be a big reason behind the depression that many suffer from, and the best answer could simply be to put on a mask and hit the sack.

Obstructive sleep apnea is characterized by airways that become constricted during deep sleep. It can result in a stoppage of breathing for a few seconds to a few minutes, and then the brain suddenly realizes what is happening and wakes up the body to resume breathing, interrupting sleep. In OSA sufferers, this by definition happens at least five times per night, preventing them from getting the deep REM sleep they need each night. Those that don’t get enough sleep often wake up feeling fatigued.

But many don’t realize they have sleep apnea. Unless they have a partner who can tell them that they snore loudly in the night or have noticed that they have these periods where they stop breathing, most aren’t aware even when they wake up that there is a problem. As a result, they go through each day feeling fatigued, thinking it is normal, and it can drag down their psyche.

We often underestimate just how important sleep is to our health. Many try to fit as many awake hours into the day as possible, leaving just a few hours for sleep rather than getting the recommended eight hours that scientists believe the body needs to completely recover and recuperate. And it’s not just the body that needs to rest: the brain also needs sleep in order to function properly, and when it doesn’t get that adequate sleep because of sleep apnea, it begins to affect one’s psyche.

The study helps illustrate just how closely intertwined sleep apnea and depression are. People with depression usually suffer from either one end of the extreme or the other: i.e., they are either insomniacs who find it impossible to get to sleep or their are hypersomniacs, who can’t seem to get enough sleep and will spend the day lying in bed. And people can suffer from both; research has found that people who suffer from both hypersomniac and insomnia are more likely to have severe and longer-lasting depression.

Then there are other disorders somewhat related to sleep that also factor into depression. You may have heard of restless legs syndrome, which is a neurological condition that causes one’s legs to feel uncomfortable while lying down at night, making it difficult to get to sleep. This condition is also heavily associated with depression, with 40 percent of RLS sufferers complaining of depression-related symptoms.

Wondering if you have depression that could be related to sleep apnea? There are a few telltale signs.

Feelings of hopelessness are one of the most common, as well as a loss of interest in activities that were once interesting. Then there is fatigue and a difficulty in concentrating. The aforementioned problems with sleep, whether insomnia or hypersomnia, are also strong signs. You may find that you are sleep in the daytime or just generally lack energy. You may notice weight gain, or that you don’t have an appetite at all. You may have lost your interest in sex. In more extreme cases, a severely depressed person will have thoughts of death or suicide — sometimes merely as a wandering daydream, other times as serious suicidal ideation. In those cases, you should contact a medical health professional right away.