The study, conducted in collaboration with University Sains Malaysia (USM) between September and December 2015 and published in the journal Beneficial Microbes, focused on 53 victims of the December 2014 flood in Malaysia.
At the time, the flood was considered one of the country's worst in decades. The resulting lack of environmental hygiene led to exposure to elevated levels of pathogenic bacteria, which are known to cause a variety of physical complications, including digestive illness.
This exposure can also cause psychological problems. The researchers wrote: "Individuals in a community who developed irritable bowel syndrome (IBS) after major floods have significant mental health impairment."
Professor Lee Yeong Yeh, from USM's School of Medical Sciences, said in a media statement: "We conducted research involving 53 victims of the flood and found some significant differences in the composition of microbiota between subjects with and without abdominal abnormalities.
"Through supplementation with Bifidobacterium infantis M-63, we succeeded in significantly alleviating the mental stress of those subjects with abdominal abnormalities."
The gut-brain axis
Knowing that flood victims require medical intervention not just during disasters but also in the recovery period, Morinaga and USM sought to assess the impact of B. infantis M-63 intake on the symptoms, psychological health and overall quality of life of participants with IBS.
They also wanted to find out if any improvement they would observe was mediated by changes in the gut microbiota.
Among the participants, 20 with IBS were each administered one sachet of B. infantis M-63 powder daily for three months, while the rest, who had no digestive issues, were treated as controls and not given the probiotic.
The researchers used the quality-of-life (QOL) SF-36 Questionnaire to evaluate the participants' mental state before and after the intervention, and conducted comprehensive analysis of their intestinal microflora using their faecal samples.
Ultimately, 11 participants in the treatment group and 20 of the controls completed the study according to protocol, and in both full analysis and per-protocol conditions, improved mental well-being was reported in the former group when compared with the latter.
Among the same 11 participants in the intervention group, the researchers observed differences in anxiety and bodily pain. When compared to the controls, the intervention group also displayed a lower ratio of Firmicutes / Bacteroidetes, which correlated with a higher post-intervention mental score.
Before treatment, the supplemented participants had an average pre-intervention total mental component score of 75; this rose to 83.1 after treatment. Their mental well-being score also improved, from 70 before treatment to 86 after treatment.
Despite this, the researchers acknowledged that their study could have been compromised by a lack of randomisation and placebo, as well as a small sample size of the intervention group due to "difficulty in recruitment of community-based participants".
Additionally, the study was conducted in a "challenging rural setting after floods" on "vulnerable individuals who were badly affected by floods and had not been exposed to such interventional studies before".
As such, it was possible that the supplemented participants might have had a beneficial placebo response or confirmation bias that led them to believe B. infantis M-63 was sure to improve their condition, thereby reducing their anxiety.
The researchers concluded that the study showed "a significant improvement with probiotic B. infantis M-63 on the mental well-being of flood-affected individuals with IBS".
"This improvement is possibly mediated by restoration of microbial balance and the gut-brain axis. However, our conclusion must be interpreted in the context of our study limitations. Future larger randomised studies are needed to confirm the findings of our study."
The probiotic used in the study, B. infantis M-63, had been shown in previous trials to be effective in strengthening immune defence against foreign invaders, as well as in improving symptoms of occasional constipation and / or diarrhoea when consumed in combination with other Bifidobacteria (namely, Bifidobacterium longum BB536 and Bifidobacterium breve M-16V).
Recent findings on the benefits of probiotics for mental health have given rise to further exploration of the gut-brain axis, which Dr Xiao Jinzhong, GM of Morinaga Milk's Next Generation Science Institute, said is "at the cutting edge of recent worldwide probiotics research".
In its official release, Morinaga said awareness of and research into the gut microbiome's multi-faceted influence on health have been growing, with health concerns such as digestion, weight management, immunity, and even mental health being "linked to a person's intestinal microflora".