The assertions were made in a letter to the editor of the European Journal of Epidemiology titled, ‘Publication biases in probiotics’ late last year.
It stated in part: “In humans the investigator hypothesis and the sponsor interest were both in favor of a probiotic effect on digestive diseases that may have led to the unreport [sic] of opposite results”.
The letter went on to say conflicts of interest were also under-reported.
ISAPP said the statements were unfounded and that it supported publication of all probiotic human trials along with the registration of trials before they begin.
“We disagree with this statement, which is not supported by any specific evidence," ISAPP said. "In addition, the term ‘opposite results’ is unfortunate, since the ‘opposite’ of a health benefit is presumably a negative health impact. This implies that probiotic investigators may be concealing evidence that probiotics may pose a threat to human health.”
“The authors presumably mean that studies failing to document a benefit from probiotic intervention (null studies) are under-reported. While this may be the case, it is well known that journals tend to accept and publish positive clinical studies to a greater extent than ones that fail to demonstrate a benefit.”
Systematic reviews
The California-based group pointed out however that many systematic reviews of probiotic clinical trials included, “null studies”.
“Indeed, in some cases the conclusion of these systematic reviews is that there is either inconclusive or insufficient evidence to merit a recommendation for probiotic use in a given indication. This is scarcely a testament to an under-reporting of null studies.”
“We submit, therefore, that there is no evidence that publication bias is more prevalent in the reporting of clinical trials involving probiotics than is the case for any other therapeutic category.”
Conflict of interest
ISAPP challenged the two letter writers to name and shame conflicts of interest abuse, if they knew of specific instances where this had occurred.
“If Million and Raoult are aware of instances where scientists in any field of study conceal data because the outcomes ‘were not the initial work hypothesis, or the funding purpose’, they should challenge those scientists directly, rather than make broad statements about probiotic research or any other discipline of scientific investigation,” it wrote.
The probiotic research literature amounts to around 7000 papers published over several decades.
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