A snapshot of how gut microflora influences mental health…
A healthy balance of gut bacteria is essential to your health. Weighing in excess of 1kg, the gut microflora has important and diverse roles to play in immune health and digestive function. It produces antimicrobial peptides, short chain fatty acids and essential vitamins too. In recent years, scientists have started to identify ways in which the gut microflora may also have a significant influence on brain function, behaviour and mental health; an exciting area of research now referred to as the microbiota-gut-brain axis.
Gut bacteria influence mental health from an early age
It is likely that gut microflora starts to affect mental health very early in life - current research suggests that brain development in growing infants is influenced by the delicate balance of bacteria in the gut. And the converse is also true - early life stress can have a lifelong impact on the microbial content of the intestine and can permanently alter immune functioning. That early life stress can also impact on adult mental health has also long been appreciated in psychiatry1.
Early animal studies show probiotics reduce anxiety and depression
We now know that gut bacteria are prolific producers of neuroendocrine hormones, as well as other neuroendocrine chemicals. In a 2011 animal study, mice fed probiotics displayed reduced anxiety-like and depressive-like behaviour. The researchers also noted changes in the levels of the neurotransmitter GABA (gamma amino butyric acid) in the brain following the administration of probiotics. This is significant because GABA is the main inhibitory neurotransmitter in the brain and regulates many physiological and psychological processes. Dysfunction of the GABA system is implicated in anxiety and depression2,3.
Preliminary human studies back these findings
In a 2011 study published in the journal Gut Microbes, probiotic supplementation improved symptoms of anxiety and depression in healthy human subjects. A 2015 randomised, placebo-controlled trial involving 70 petrochemical workers found supplementation with probiotics to have beneficial effects on mental health parameters as assessed via general health questionnaire (GHQ) and depression and anxiety scores (DASS). Another 2015 study found probiotics improved sad mood in healthy human volunteers4-6.
Links between gastrointestinal and mental health problems
There are long established links between gastrointestinal problems and psychiatric neurological disorders such as anxiety, depression, autism, schizophrenia and neurodegenerative disorders - a high comorbidity between functional gastrointestinal disorders and stress-related psychiatric disorders such as anxiety and depression. Research has shown that probiotics can modulate the stress response and improve mood and anxiety symptoms in patients with irritable bowel syndrome (IBS)7.
Now is the time to nurture a healthy internal ecosystem
Research into the interactions between gut microflora and the brain is still in its infancy; and the majority of studies up to now are animal-based. Clearly, more research is needed to fully understand this complex relationship, however in the last five years, there has been an amazing increase in knowledge of how bacteria signal to the brain and the implications this may have for treatment approaches to mental health. Scientists agree that modulation of the gut microflora with novel therapeutics may become a useful strategy to support the growing burden of mental health problems in the future.
For now, it’s prudent to nurture a healthy internal ecosystem, right from birth as there are significant and widespread benefits for your physical health and very likely for your mental health too. Click here to find out some simple ways to nurture healthy bacteria for good.
1. Douglas-Escobar M, Elliott E, Neu J. (2013) Effect of intestinal microbial ecology on the developing brain. JAMA Pediatr 167:374–379
2. Bravo JA, Forsythe P, Chew MV, Escaravage E, Savignac HM, Dinan TG, Bienenstock J, Cryan JF. (2011) Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA 108:16050–16055.
3. Cryan JF, Kaupmann K. Don't worry 'B' happy!: a role for GABA(B) receptors in anxiety and depression. Trends Pharmacol Sci. 2005 Jan; 26 (1): 36-43
4. Messaoudi M, Violle N, Bisson JF, Desor D, Javelot H, Rougeot C. 2011b) Beneficial psychological effects of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in healthy human volunteers. Gut Microbes 2:256–261.
5. Steenbergen L, Sellaro R, van Hemert S, Bosch JA, Colzato LS. (2015) A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain Behav Immun 48:258–264.
6. Mohammadi AA, Jazayeri S, Khosravi-Darani K, Solati Z, Mohammadpour N, Asemi Z, Adab Z, Djalali M, Tehrani-Doost M, Hosseini M, Eghtesadi S. (2015) The effects of probiotics on mental health and hypothalamic-pituitary-adrenal axis: a randomized, double-blind, placebo-controlled trial in petrochemical workers. Nutr Neurosci. Epub 16 Apr 2015.
7. Foster JA, Lyte M et al. Gut microbiota and brain function: An evolving field in neuroscience. Int J Neuropsychopharmacol. 2016 May; 19(5): pyv114. Published online 2015 Oct 4. doi: 10.1093/ijnp/pyv114
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