We’re often told there’s no objective test of insomnia. Brain waves aren’t very revealing when it comes to distinguishing insomniacs from normal sleepers. Tests of heart rate variability and metabolic rate have shown slight average differences between groups of people with and without insomnia, but they would not distinguish an individual insomniac from a normal sleeper.
Now a research group in Switzerland is claiming they’ve found an objective marker of insomnia: brain-derived neurotrophic factor, or BDNF.
What Is BDNF?
BDNF is a protein that promotes the survival of nerve cells and the growth of new neurons in the brain and spinal cord. It facilitates communication between neurons, which is important for learning and memory. In addition, BDNF is active in areas of the brain that control appetite and—importantly for this blog post—sleep.
BDNF, Stress, and Mood Disorders
But let’s forget about sleep momentarily and consider the impact of stress and mood disorders (two factors known to have a relationship to sleep) on BDNF levels. Acute stress—meaning stress that is relatively intense and short lasting—leads to an increase in BDNF levels. This increase in BDNF appears to play a part in helping us respond to a stressor, whether internal or from without. Our bodies fight off an infection. We escape from an attacker. BDNF levels return to normal.
But chronic stress (think of chronic inflammation or repeated sexual assaults) tends to decrease BDNF levels. In turn, low levels of BDNF, combined with predisposing and other precipitating factors, increase people’s susceptibility to mood disorders such as major depressive disorder. The neurotrophic hypothesis of depression holds that stress-related mood disorders occur due to a stress-induced decrease in BDNF expression.
Sleep and BDNF
It’s axiomatic now that stress has a relationship to sleep, negatively impacting sleep quality. In turn, poor sleep makes us less resilient to stress. Depression, too, has a close relationship to sleep: sometimes depression gives rise to insomnia and in other cases insomnia leads to depression. But until recently, there was little research on the impact of sleep and stress-related insomnia on BDNF levels.
So the Swiss researchers tackled the problem, assessing levels of BDNF in the blood serum of adults with and without insomnia. A total of 50 participants were screened for insomnia and divided into insomniacs (26) and normal sleepers (24). Here are the key findings:
- Participants currently suffering from insomnia symptoms had significantly lower serum BDNF levels than the normal sleepers.
- BDNF levels were significantly correlated with insomnia severity. The greater the insomnia severity, the lower the level of BDNF.
BDNF, Tiredness, and Fatigue
The same team examined the BDNF levels in 12 men who had recovered from occupational burnout. The investigators found that BDNF levels were significantly lower in the men reporting tiredness and fatigue (daytime symptoms associated with insomnia) than in men who did not report these symptoms.
Based on their results, the researchers have come up with a hypothesis. They suggest that chronic stress deregulates the body’s stress system, leading in the long term to insomnia and decreased BDNF levels. Thus low levels of BDNF may be an objective marker of insomnia. They also might account at least in part for the tight relationship between insomnia and depression.
Acute Sleep Deprivation Increases BDNF
There’s some good news in all of this. Remember that while chronic stress lowers BDNF levels, acute stress increases levels of BDNF.
Many studies have shown that acute sleep loss—loss of an entire night’s sleep, for example—leads to a rapid increase of BDNF in the brain. Even partial sleep deprivation, an acute stressor for the brain, seems to work this way. And increased brain BDNF is associated with improved sleep.
If this sounds like talk about sleep restriction, it should. In fact, the sleep investigator who sent the article on which this post is based made the claim outright, saying, “This is why sleep restriction works.”
Find more information about sleep restriction in my book, The Savvy Insomniac, and by clicking Blog at the top of this page. Type “sleep restriction” into the site search box and graze away.