A huge amount of information travels along the nerves that supply the gut, both from the brain to the gut and from the gut to the brain. There is so much nerve activity in the gut that it has sometimes been called our “second brain”.1-4 These connections between the gut and the brain influence so many aspects of our life: hunger levels,5 mood,6,7 how well we digest our food, how food moves through the gut8 and sleep.9 If you doubt the strength of these connections, think how stage-fright can make a person feel sick!
Sleep and the gut
It’s been known for years that not getting enough sleep can increase hunger levels and lead to obesity.5 Interestingly, our gut bacteria are affected by our body rhythms of sleep and wakefulness.9 This change can happen very quickly: studies of jet lag show changes in the balance of the gut bacteria, which reverse when the person is no longer jet-lagged.10,11 In an experiment where animals had their sleep deliberately disrupted, within a week their gut bacteria took a turn for the worse – favouring bacteria that are linked with inflammation (and at the same time their blood pressure increased).12 It even seems that our gut bacteria may be able to influence our genes that control these rhythms!13 Thus, the composition and characteristics of our gut bacteria are linked to our sleep patterns.
We know that our gut bacteria can communicate with the brain because they can influence the manufacture of several chemicals that our bodies use to send signals along our nerves, including serotonin and dopamine.14 This is important because serotonin and dopamine are key players in our moods.15 And, from the point of view of affecting sleep, serotonin is used by the body to make melatonin (aka the sleep hormone). Around 90% of the serotonin in our bodies is produced in the gut so the health of our gut is clearly going to be relevant to how well we make melatonin and hence our ability to sleep well.
On the downside, if we have an imbalance in our gut bacteria, the less helpful bacteria can make chemicals that can contribute to insomnia, such as ammonia and lactic acid.15,17
Changing the gut bacteria can improve sleep
Problems with insomnia often go alongside gut issues. People with irritable bowel syndrome (IBS) are more likely to have sleep issues than those without.18 Measures to improve the balance of the gut bacteria have been shown to improve sleep.9 For example, certain prebiotic fibres that specifically provide food for bacteria that promote serotonin can improve sleep quality.19,20
Can better sleep translate to better gut health?
Of course, getting a good night’s sleep depends on other factors than simply feeding the right gut bacteria. Most important is the timing of our exposure to light and dark.21 Changes have been seen in numbers of certain gut bacteria that correspond to our light and dark cycles.11 As noted above, recovery from jet-lag and stopping disrupting the sleep of the experimental rats resulted in changes in the gut microbiome for the better.
Get a better night’s sleep
If you experience disrupted sleep, have trouble getting off to sleep or wake up very early in the morning, or regularly get less than 6 hours of sleep, read our article on how to improve your sleep here.
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