Is there really a link between probiotics and depression?

According to the mental health charity Mind, one in four people will experience a mental health problem of some kind each year in England, and one in six people report experiencing a common mental health problem (like anxiety and depression) in any given week.

Globally, depression remains a leading cause of disability. A recent UK survey found that the prevalence of depressive symptoms ranged from 3.3 per cent to 11.3 per cent (depending upon the severity), with a peak reporting of these symptoms in middle adulthood.

Treatments may include pharmaceutical medication, psychological programmes (such as talking therapies) and social programmes (such as social prescribing, for example joining a local group with a shared interest; like gardening or walking). Overall, there is good evidence for the effective use of conventional medication. 

Having said this, around 60 per cent of people with major depressive disorder experience some degree of non-response to first-line treatments and around a third continue to experience symptoms despite further treatment. Many individuals (as well as practitioners) are therefore keen to explore additional options for managing depression-related symptoms. 

As research continues to explore the role that the gut microbiome plays in human health, more evidence is beginning to emerge around the communication network between the gut microbiome and the brain, referred to as the "gut-brain axis". 

For many years, it had been widely accepted that our emotional state may affect the rate of digestion. It took many more years however, to consider that alterations in gut physiology may cause emotional changes. Since then, reports of gastrointestinal disturbance within neurological conditions have become more prominent and in some instances, digestive symptoms have been a complaint years before the onset of some neurodegenerative symptoms.

An additional factor in gut and mental health is the balance and types of microorganisms within the gut. Interestingly, having an imbalance of beneficial gut bacteria has been associated with mood disorders, therefore research into modulating the gut microbiome remains active and ongoing. The role that the gut microbes play in the communication of the gut-brain axis has been suggested to be so important, that scientific papers will often refer to this pathway as the "microbiota-gut-brain axis". 

Evidence suggests that supplementing with live bacteria to support gut and mental health may be beneficial, through the use of bacterial metabolites and their potential ability to act as neurotransmitters, immune-modulators and anti-inflammatory compounds. Given the range of actions that these microbes may offer, it may be useful to consider supplementing with a range of different bacterial strains, as each strain of beneficial microbe will exhibit different characteristics—much like different people in a workplace (all with their individual strengths).

Another important aspect for deciding upon a supplement, would be the clinical evidence that supports the product. Bio-Kult Everyday contains 14 different strains of live bacteria and has been used in a variety of human clinical trials. 

Last year, this multi-strain product was found to significantly improve mood scores in individuals with self-reported low mood. Seventy people were randomised into two groups and after four weeks, the supplemented group reported a 50 per cent improvement in low mood scores as well as improvement in concentration.

More recently, a study published this year found that after supplementing with a multi-strain product alongside usual medications, individuals with depression had significantly improved scores. The Hamilton Depression Scale (HAMD) reduced by 34 per cent after 4 weeks and after 8 weeks, the Inventory of Depressive Symptomatology (IDS) score reduced by 33 per cent alongside the Hamilton Anxiety Rating Scale (HAMA) which reduced by 48 per cent.

These results are very promising, as they show that tolerability and the estimated effect of live bacteria supplements in this subject group are positive and it encourages further research in this area!