Sleep and mental health: A two-way street

If you’ve ever experienced a mental health condition, you may have noticed that it interferes with sleep. And if you’ve ever missed a night’s shut-eye, you know how it can impact your mood.

But what’s the nature of this relationship? And how are they linked? In this article, we’ll try to answer these questions.

The size of the problem

Sadly, many of us struggle to get a good night’s sleep. Around 1 in 3 people report that they’ve experienced symptoms of insomnia. This includes trouble dropping off, as well as waking up during the night or waking up too early.

Mental health conditions are common, too. For example, around 1 in 20 adults in the United States regularly feel depressed. And 1 in 10 often feel worried, anxious, or nervous.  

In England, around 1 in 6 people have a mental health condition. Globally, the figure is about 1 in 8 people.

Getting to grips with the two types of conditions should be a public health priority. And understanding how mental health and sleep are linked could provide new avenues for treating both.

Chicken or egg?

For some time, scientists have known that mental health conditions are associated with poor sleep. 

Initially, they thought that poor mental health came first, leading to sleeping problems. This is called secondary insomnia.

Scientists widely believed that the best approach to fixing secondary insomnia was treating the primary condition — depression, for instance.

For instance, one study showed that people without depression who have insomnia are twice as likely to develop depression in the long run. Another study, this time in children, found that “Sleep problems at age 8 predicted depression at age 10.”

And a review on the topic concluded that the “best available evidence suggests that insomnia is bidirectionally related to anxiety and depression.” 

In other words, sometimes the chicken comes before the egg, and sometimes the egg comes before the chicken. 

Scientists now think that in many cases, insomnia — whether it starts before or after a mental health condition — can make mental health symptoms worse. 

To stretch the classic metaphor way past its breaking point: Regardless of which came first, sometimes, the egg exacerbates the chicken and vice versa.

Other conditions

Although most research in this area has focused on links between insomnia, anxiety, and depression, some scientists have looked at other conditions. 

Also, several sleep disorders have been linked to mental health conditions. 

Sleep apnea is one example. People living with this condition stop breathing multiple times throughout the night. It affects an incredible 1 billion people worldwide. And studies have shown that these people are more likely to have mental health conditions.

Similarly, depression is associated with restless leg syndrome. This causes irresistible urges to move the legs, particularly at night, which can cause insomnia.

 Sleep as a treatment

If poor sleep worsens mental health symptoms, could improving sleep help reduce the symptoms?

One review set out to find answers. The researchers scoured journals for randomized controlled trials — the gold standard of medical research. 

Specifically, they looked for studies in which scientists had successfully changed participants’ sleep in some way, then assessed their mental health at a later date.

In all, the team identified 65 studies, which included a total of 8,608 participants.

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The studies had manipulated sleep with a wide range of techniques, including cognitive behavioral therapy (CBT), acupuncture, tai chi, walking, medicines, and herbal remedies. 

Importantly, the authors of the review only included studies if the researchers had shown that their interventions really did improve people’s sleep.

When looking at how these sleep interventions affected mental health, there was a great deal of variety. 

But once they’d cleaned up the data, the authors found, on average, a statistically significant “small-to-medium-sized” improvement in mental health an average of 20.5 weeks later.

They saw the clearest mental health benefits in participants with depression, anxiety, or stress.

The researchers also found that the greater the improvement in sleep, the greater the improvement in mental health. They write:

Why are sleep and mental health linked?

Scientists have a range of theories about why insomnia and mental health conditions are so tightly linked. We’ll outline a few below.

No one knows which theory is correct, but it’s possible that they’re all playing a part in some way — everyone is different, and mental health conditions vary considerably.

Neurobiology

Serotonin is a neurotransmitter. It plays a role in sleep, although exactly what it does is still up for debate. One theory about how depression works is that people with depression have lower serotonin levels. 

But we should note that the serotonin theory of depression has recently received a bit of a bashing. As it stands, it’s unclear how important this neurotransmitter is in the condition. 

Regardless, there may be other neurotransmitters and pathways that link mental health conditions and insomnia. Another example is dopamine, which appears to play a part in both insomnia and depression.

A role for inflammation?

Inflammation is a healthy response to infection and injury, but it can damage your body if it lasts for a long time.

Some experts have wondered whether inflammation might disrupt sleep and influence mental health conditions.

For instance, some research shows that different types of inflammatory response are linked to both sleeping too long and being unable to get enough sleep.

At the same time, there's evidence that anxiety, depression, and other mental health conditions are associated with inflammation.

Stressors

Stress might be a factor that draws insomnia and mental health together.

The way an individual handles stress might also make a difference. For example, people with depression tend to handle stress less effectively. And the same is true for people with insomnia. 

So it might be that, for some people, how they react to stress increases the likelihood of both sleep problems and mental health conditions.

What about genes?

There is some evidence that people with depression and people with sleep disturbances share differences in their circadian genes.

These genes help control your sleep-wake cycle. And disruptions in circadian rhythms are also linked to other mental health conditions, such as bipolar disorder.

So, potentially, if circadian gene variants are associated with insomnia and mental health, genetics might explain some of this relationship in some people.

More to discover

All or none of the above explanations might be correct. Scientists need to carry out more research into this complicated relationship. But what seems increasingly clear is that sleep disturbances and mental health conditions are tightly welded together.

Understanding how this relationship works might help scientists uncover novel ways to treat both.

For instance, ICBT-i, a form of CBT that treats insomnia over the internet, may be a valuable way to address sleep and mood issues. 

A meta-analysis looked at 10 randomized controlled trials involving ICBT-i. The authors concluded that ICBT-i did improve people’s insomnia, and it also improved symptoms of depression and anxiety.

This is just a start, though. And with millions of people experiencing mood disorders and sleep problems, uncovering better ways to handle them is vital.