Probiota Asia 2018

More effort required: Less than 1% of studies on neurological diseases feature probiotics

By Tingmin Koe

- Last updated on GMT

Ger Rijkers is the professor of Biomedical and Life Sciences at University College Roosevelt, Netherlands.
Ger Rijkers is the professor of Biomedical and Life Sciences at University College Roosevelt, Netherlands.

Related tags Probiotics Clinical trials gut-brain axis Digestive health

Out of 11,018 studies conducted on neurological diseases, only 23 examined the effects of probiotics on the diseases. This was less than 1% of all studies done, a review of clinical studies has found.

“To me, that is disappointing,”​ said Ger Rijkers, professor of Biomedical and Life Sciences at University College Roosevelt. He urged for more research on the gut-brain axis.

 “We as the researchers and you as the industry should put in more effort. I think the gut-brain axis is so important and so well-known that there should be potential for probiotics in this field.”

He gave the example of dementia, where only five out of almost 5,000 studies examined the effects of probiotics on dementia. 

A review of the existing studies from and the World Health Organisation was conducted. Rijkers revealed results of the review during his presentation at Probiota Asia.

Studies involving probiotics mostly surrounded its efficacy on alleviating gastrointestinal problems.

Citing data from, seven out of 10 studies focused on the effects of probiotics on gastrointestinal problems, such as digestive system, intestinal, and colonic diseases.  

On the other hand, there was an increase in the number of studies conducted on microbiota as compared to probiotics in the past 10 years.

In fact, the number of trials involving microbiota has surpassed that of probiotics in year 2013. Since then, microbiota trials have consistently outnumbered probiotics trials.

A search on showed that 1,073 studies involved probiotics, while the figure for microbiota was 1,274.

As for bacteria types, lactobacillus was the most commonly studied bacteria - with 706 studies conducted. This was followed by bifidobacterium, with 348 studies conducted.

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Probiotics clinical trials – small and underpowered?

Rijkers refuted the claim that clinical trials conducted on probiotics were small-scale and therefore, underpowered.

 “We counted all studies that were done on gastrointestinal diseases on​. There were over 10,000 studies. On average, those studies have 71 participants. Studies with probiotics were around the same, with 74 participants, so these studies were not small-scale, they were of average size.”

In addition, the probiotics studies also involved healthy subjects, although the majority involved patients.

For instance, 43% of the probiotics studies consisted of healthy individuals. This was especially so in Europe where the regulations required the involvement of healthy subjects.

Most of the probiotics studies occurred in Europe (415), followed by the US (207).

Elsewhere in Asia, most of the probiotics studies took place in China (79).

Moving forward, he pointed out that most probiotics studies would be conducted in Europe, with 90 studies that are already recruiting or have yet to recruit participants. This is followed by the US (38) and China (18).

Problems with study registration

Only 32% of the studies were registered before the inclusion of the first participant, which Rijkers said was an area of concern.

When you register a clinical study, you should do that before the study starts, not when the study is ongoing, or when the study is completed."

“And there are studies that are registered more than two years after the first patient has been included. And that is a major sin, it should not be that way."

“You should at least register your trial before the study is completed, and fortunately, that is the case with 78% of the studies but still, you see studies that are registered after completion.”

The problem with registering the study after patients were recruited, he explained, was that the researchers “would be tempted to formulate the primary outcome of the study based on what they have found and not on what they have intended to find.”

He also pointed out other problems observed in the clinical studies conducted.

For instance, nearly 450 studies on did not have a complete data on the number of strains studied.

Others did not state the bacteria count, which he said, was another area for improvement.

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