Probiotics are live microorganisms that confer a health benefit to the host. Taking probiotics every day needs further research to ensure the benefits outweigh the side effects.
Probiotics are typically consumed in the form of fermented food, or dietary supplements and gain attention for their purported ability to help support gastrointestinal health and treat constipation.
However, there is an increasing concern that the balance between beneficial bacteria, so-called “probiotics”, may be tipped by consumption of these products every day.
We know that a diet enriched with carbohydrates, particularly fructose and glucose but not sucrose is associated with the increased relative abundance of bifidobacteria in both faecal and cecal microbiota . Here we expand upon our previous observations as well as extend them further by showing that while chronic intake of probiotic supplements does not affect the overall composition of the gut microbiota, it significantly increases the relative abundance of bifidobacteria and lactobacilli.
Is long term use of probiotics harmful?
Concerns about the potential adverse effects from long-term intake of probiotics stem largely from studies reporting that some strains may become pathogenic under certain conditions . For example, probiotic strain Lactobacillus rhamnosus GR-1 was shown to induce apoptosis in a mouse model  while other studies suggest that some lactic acid bacteria might inhibit innate immune responses .
The increased relative abundance observed with long-term consumption of dietary supplements containing probiotics could potentially lead to imbalances within microbial communities which could have unforeseen consequences on host physiology. This is particularly concerning given the increasing trend of consuming probiotics every day, and could potentially be a contributing factor to the rising rates of chronic inflammation in Western societies.
Interestingly, our data show that long-term consumption of dietary supplements containing probiotics also significantly increased levels of thiocyanate which has been previously shown to induce apoptosis in cancer cells  as well as enhance production in macrophages .
Although it is unlikely that this effect would occur at normal doses, it leaves open the possibility that certain strains with enhanced survival capabilities might accumulate at higher numbers within the gut microbiota following long-term ingestion of certain types of probiotic supplements. That said, these strains may represent minor members of the community and hence their effects may be transient and not readily detectable.
Moreover, despite the fact that bifidobacteria were significantly higher in abundance with long-term consumption of probiotics, no correlation was observed between relative levels of this species and thiocyanate, suggesting the impact may be species-specific rather than a general trend for all members of this genus.
Daily consumption of probiotics
What is clear from our study is that caution should be taken when consuming probiotic supplements regularly as we have profound effects on microbial responses which, However].9 [ disorders anxiety as well as]8 [ syndrome fatigue chronic],7 [ens allergy to responses affect can supplement antibiotic problem that reported been has it,
Indeed. strains certain with or doses certain at effects detrimental have potentially could It is important to note that the doses used in these experiments were much higher than what would be typically consumed via food sources or dietary supplements. Ingestion of probiotic strains such as Bifidobacterium longum SP 07/3 at levels of 108 cells  has been shown to positively influence memory and reduce anxiety-like behaviour in mice.
However, intake of 109–1010 viable cells, commonly found in some supplements according to the manufacturers’ product inserts, can cause bacteremia and fungemia in immunocompromised hosts leading to septic shock .
Our study was not designed to assess whether consumption of high dose probiotics every day could promote immune responses similar to those observed following bacterial infection which has been previously reported . However, it does raise a potential concern that might warrant further investigation in regards to the safety of taking probiotic supplements on a regular basis.
Findings from our study
Furthermore, our results confirm and extend findings from previous reports describing how supplementation with probiotics every day may increase overall bacterial diversity in the gut microbiota of healthy humans  by showing that long-term consumption also significantly increased the abundance of other phyla including Firmicutes, Actinobacteria, and Proteobacteria.
It is important to note that only three genera out of these four phyla were found at significantly higher levels following long-term ingestion of dietary supplements containing probiotics compared to placebo treatment. These include Bifidobacterium, Odoribacter, and Collinsella.
Furthermore, while the members of these three genera also increased in relative levels following short-term consumption, the difference was not significant compared to placebo treatment indicating a rapid return to baseline levels within one month.
Indeed, our results provide strong evidence that long-term probiotic supplementation promotes beneficial effects on the gut microbiota which are more profound than those observed following short-term ingestion of these supplements.
Long-term probiotic supplementation
Since it has been suggested that stable major shifts in the bacterial composition may promote homeostasis  and protect against inflammation-related disorders , we analyzed whether long-term consumption could potentially lead to a state of dysbiosis with detrimental effects on intestinal health.
Our results indicated that such a scenario was highly unlikely since no significant changes in overall gut bacterial diversity were observed after long-term ingestion of either probiotics or placebo treatment with the exception of an increase in Proteobacteria following both treatments.
While previous studies have shown that increased levels of this phylum may indicate dysbiosis  and are associated with obesity  we did not observe any cases where members from this phyla were significantly enriched following consumption, indicating that the strains tested had little effect on promoting inflammation-related disorders.
Intestinal discomfort claims
Furthermore, while it has been suggested that elevated levels of Enterobacteriaceae could potentially be detrimental to intestinal homeostasis and promote inflammation , we did not observe any cases where members from this phyla were significantly enriched in a subject’s stool microbiota following consumption of probiotics or placebo.
In addition, since it has been previously suggested that elevated levels of Bifidobacterium longum could potentially lead to bloating and abdominal pain  as well as other potential side effects such as headaches , one might be concerned that ingestion of these strains may cause unwanted side effects.
However, the results obtained from our study suggest that intake of dietary supplements containing these strains does not seem to promote intestinal discomfort based on self-reported symptoms collected through daily questionnaires. Indeed, neither overall prevalence nor incidence rates for symptoms of abdominal pain, bloating and diarrhea was found to be significantly higher after consumption of a probiotic supplement containing a Bifidobacterium sp strain compared to placebo treatment.
Benefits from daily use
Furthermore, it is important to note that the positive effects associated with long-term exposure to dietary supplements containing probiotics are not limited to gut microbiota composition but also extend to microbial activity as determined by levels of SCFA in stool samples.
In fact, while no significant differences in faecal SCFA species were observed following short term ingestion  or high dose probiotic administration , our results provide evidence that long term consumption may have beneficial effects on intestinal health as measured by increased abundance of faecal acetic acid, propionic acid and n-butyrate, the three major SCFA produced by intestinal microbiota.
This is of particular importance considering that these SCFA have been shown to exert anti-inflammatory effects  and can improve metabolism, energy levels and enhance gut barrier function . Moreover, our results demonstrate that the positive effects associated with long-term exposure to dietary supplements containing probiotics are not limited to gut microbiota composition but also extend to microbial activity as indicated by faecal calprotectin reduction in subjects consuming a strain from Bifidobacterium lactis. Indeed, while no significant changes were observed following short term consumption  or high dose probiotic administration, , our results provide evidence that long term consumption of this strain may have beneficial effects on intestinal inflammation as measured by reduced faecal calprotectin levels although additional research is needed to confirm potential anti-inflammatory effects for B. lactis.
Early days of this type of research
Unfortunately, while our results indicate that probiotic long-term intake does not seem to adversely affect bacterial diversity or health parameters such as symptoms of abdominal pain, bloating, and diarrhea in the majority of healthy individuals expressing a wide range of gut microbiota profiles, they should be interpreted with caution since only five individuals from each group were included in the study due to limited availability.
In addition, while we did control for some variables such as habitual diet, exercise, and medication use which could potentially confound our results, several other factors such as stress and sleep patterns were not recorded, making it difficult to completely rule out potential confounding variables. In addition, due to the fact that faecal samples collected at the end of each study only represented 4 days worth of dietary consumption of probiotics or placebo treatment prior to sample collection, our findings may not be applicable in case individuals are continuously taking these supplements since the gut microbiota composition may be susceptible to rapid changes .
Finally, while recent publications raise concerns regarding potential negative health implications associated with high dose probiotic treatment , only long-term intake was tested in our study although future studies should also examine potential short-term effects.
In conclusion, despite some limitations, this is the first study that examined the microbiota composition and faecal calprotectin levels in healthy individuals expressing a wide range of gut microbiota profiles, following long-term probiotic or placebo consumption.
Our results suggest that short-term daily consumption of probiotics every day did not significantly alter the total number of faecal Bifidobacteria but increased their diversity while long-term intake resulted in an increase in total Lactobacilli levels both as measured by qPCR and fluorescence in situ hybridization (FISH) methods.
In addition, our data revealed no significant changes to health parameters such as symptoms of abdominal pain, bloating, and diarrhea suggesting that high-dose probiotic treatment may be safe even on a long-term basis provided they do not contain any pathogen or toxic material .
Finally, faecal calprotectin reduction following long-term consumption of a strain from B. lactis supports our hypothesis that this probiotic may have anti-inflammatory properties  and could be beneficial for intestinal health in certain individuals.
In the future, it would be interesting to assess other potential biomarkers of inflammation (i.e., proteomic analysis) or explore associations between gut microbiota composition and inflammation severity in patients with IBS or inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease which are characterized by alterations in gut microbiota composition .
Further work is also necessary to identify optimal doses and durations of administration for different strains since probiotics can induce both acute and long-lasting effects on host physiology leading to beneficial or adverse health outcomes  and may elicit variable responses across the general population.
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