Probiotics boost serotonin levels in patients with IBS, subthreshold depression – study

By Tingmin Koe

- Last updated on GMT

A woman with stomach cramps resting on the sofa. © Getty Images
A woman with stomach cramps resting on the sofa. © Getty Images

Related tags Irritable bowel syndrome Probiotics Depression

Drinking cultured milk containing two probiotic strains could improve serotonin levels in individuals suffering from irritable bowel syndrome (IBS) and subthreshold depression, according to findings from a 12-week study conducted in Malaysia.

Serotonin is functions as a neurotransmitter and plays a role in boosting mood. Low levels of serotonin are linked to depression.

While serotonin had increased, there was no significant reduction in the serum levels of cortisol – the stress hormone, the researchers from Universiti Kebangsaan Malaysia and Sunway University wrote in Scientific Reports.

The 12-week randomised, double-blinded, placebo-controlled, parallel clinical trial involved 124 IBS patients.

They were either suffering from subthreshold depression or had normal mood, based on their depression symptoms score derived from “Center for Epidemiologic Studies Depression Revised” (CESD-R) questionnaire.

This is a self-reported questionnaire. Subthreshold depression is defined as having a score of 16 and above, while normal mood is defined as having a score of below 16.

They were randomly assigned to one of the four following groups: 1) IBS and normal mood on placebo 2) IBS and normal mood on probiotic 3) IBS and subthreshold depression on placebo and 4) IBS and subthreshold depression on probiotic.

The probiotic consumed was 125ml bottle cultured milk containing 1bn CFU of Lactobacillus acidophilus​ (LA-5) and Lactobacillus paracasei ​(L. CASEI-01). Those taking the probiotics had to take two bottles daily.

Researchers then measured the change in depression symptoms score using the CESD-R questionnaire.

They also assessed changes in patients’ IBS-related quality of life, gastrointestinal symptoms and conducted hormonal analysis of cortisol and serotonin.

A total of 110 patients completed the trial.

Findings showed that only patients with subthreshold depression and taking probiotics showed a significant rise in serotonin serum levels.

“Serotonin serum levels among IBS-SD (subthreshold depression) participants with probiotic increased significantly with mean difference of 0.166,”​ said the researchers.

Probiotics intake did not lead to any significant changes in the serum serotonin levels of IBS patients with normal mood.

While serotonin levels had improved, probiotics intake did not significantly improve cortisol levels in IBS patients with subthreshold depression.

“The cortisol serum level in IBS-SD participants did not significantly change despite an increasing pattern following probiotic intervention,”​ said the researchers.

“Our current findings were consistent with a recent trial that demonstrated no significant reduction in cortisol levels after 4-week of probiotic consumption,” ​they added.  

They also acknowledged the need for more studies to further validate the efficacy of probiotics in improving serotonin levels.

“Despite the favourable change in serotonin levels caused by probiotics, the superiority of probiotics cannot be determined merely by this study,” ​they said.

Irritable bowel syndrome is frequently linked with coexisting mental illnesses. A previous study​ discovered that 32.1 per cent of IBS patients had subthreshold depression, placing them at a higher risk of developing major depression.

Emerging findings of the gut-brain axis have led to rebranding IBS as a disorder of gut-brain interaction.

Depression scores improved

Self-reported depression scores had significantly improved in IBS participants with subthreshold depression, regardless of whether they took probiotic or placebo.

Both probiotic and placebo groups had significant reduction in their CESD-R scores.

“Both IBS-SD patients receiving probiotic and placebo experienced a decline in CESD-R scores resulting in more participants with CESD-R score of less than 16.

Post-intervention, 65.4 per cent and 74.1 per cent of participants who received probiotic and placebo respectively, were categorised as having normal mood.

“IBS-SD participants who received a placebo in our study also displayed a decrease in their depression symptoms.

“This finding implied that additional features such as positive attitude and perspective towards the interventional products received, may contribute to the treatment efficacy,” ​the researchers explained.

However, they also pointed out earlier studies using lactic acid bacteria had demonstrated no significant changes in depression scores among IBS patients. Similarly, supplementation with multispecies probiotics had not shown to be superior in alleviating the symptoms of depression.

Also, there was no significant changes seen in the CESD-R scores of participants with normal mood, regardless of whether they were on probiotics or placebo.

Quality of life

Quality of life had also improved significantly by 7.1 per cent to a score of 83.1 in IBS patients with subthreshold depression participants.

The most prominent improvements in their quality of life were seen in the incidence of feeling dysphoria or unpleasant mood, worries over health, and food avoidance.

Those on placebo also saw their quality of life improved significantly, which was the same case for IBS-normal mood patients on placebo.

Only IBS-normal mood participants on probiotics did not report significant improvements in their quality of life.

“Despite an increase in all IBS-QOL (quality of life) domain scores, the changes for IBS-NM participants receiving probiotic were minimal and insignificant.”

Remission in IBS

All four groups reported significant improvement in IBS severity post-intervention, with a higher prevalence of remission and mild IBS.

The IBS severity pattern shifted from a higher rate of moderate-severe levels, towards a higher rate of remission-mild symptoms across all groups at post-intervention, irrespective of placebo or probiotic-supplemented.  

For example, IBS patients with subthreshold depression and were taking probiotics had remission rates increased by 15.4 per cent.


Source: Scientific Reports

A randomized, double-blinded, placebo-controlled clinical trial on Lactobacillus-containing cultured milk drink as adjuvant therapy for depression in irritable bowel syndrome.

Authors: Sarkawi, M., Raja Ali, R.A., Abdul Wahab, N. et al.

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