By now we’ve all read the jaw-dropping statistic: a healthy human body plays host to about 10 times as many microbial cells as it does to cells of…well, of itself. Which raises the almost existential question: Where does “self” end and “non-self” begin? And if we contain more of the latter than the former, what are we, anyway? Moreover, what are they?
It’s heavy stuff. And yet it captures only in broadest outline the mysteries that researchers are untangling under the aegis of the Human Microbiome Project (HMP), the National Institutes of Health (NIH) effort charged with generating studies and data from which to characterize the human microbiome—that’s the collection of microbes that live in, on, and with us—and to analyze how it influences our health, or lack thereof.
While it’s still early days for the project, it’s no overstatement to call its potential revolutionary. As Donald. J. Brown, ND, managing director, Natural Product Research Consultants (NPRC; Seattle, WA), told an audience at the 2014 Council for Responsible Nutrition (CRN) Day of Science in November, “In the next couple of years, our worlds may be rocked” not just by what the HMP and allied investigations reveal, but by the findings’ power to shape public health and probiotic supplement research.
Brown, a naturopathic physician with a keen interest in probiotics, spoke at CRN’s Day of Science and in a subsequent interview with Nutritional Outlook about good gut bugs and the emerging science concerning them. “The really interesting thing that’s coming up that we’re all sort of holding our breath for” is what we stand to learn when researchers start correlating data about the microbiome to specific wellness and disease endpoints, he says.
He cites a 2013 study in Nature1 as offering “a snapshot of what we might expect” when those correlations start surfacing. Researchers who studied the microbial composition of 123 non-obese and 169 obese subjects found that those with “low bacterial richness”—a group comprising 23% of the study population—exhibited more overall adiposity, insulin resistance, dyslipidemia, and pronounced inflammatory markers than those with greater bacterial richness.
The takeaway is that when it comes to health, more microbial diversity is better. And while the study is new, we might have drawn a similar conclusion by examining the guts of our forebears. Why? As Brown explains, “What we’re talking about is not fast-forwarding but going back in time to understand why, when people did more hunting and gathering and were exposed to soil in their food, that created a situation that led to more diversity” in their microbiomes.
Spokes in the Gut-Health Wheel
The challenge for HMP researchers and the public health community—not to mention the dietary supplement industry—is to encourage that long-gone microbial diversity in a population not of hunters and gatherers, but of contemporary cube dwellers and consumers. And the solution, at least in part, may lie in probiotic supplements.
This realization comes at an already dynamic time for the segment, which continues to grow domestically and abroad. The Natural Marketing Institute (NMI) estimates that the category will reach a value of $44.9 billion by 2018, representing a compound annual growth rate of 6.8% from 2013.
But thus far, consumer interest in probiotics has centered mainly on how the organisms improve gut health and regularity—for good reason, as overwhelming evidence supports their beneficial role in fostering healthy digestion. But where research into the human microbiome promises to expand this picture is in sketching how the “spokes coming off the gut-health wheel,” as Brown puts it, intersect with other facets of health.
Off to a Good Start
Take, for instance, the relationship between probiotics and pediatric health. Brown points out that humans essentially have no microbiome prior to birth; only once an infant ingests vaginal fluid during delivery do microbes begin colonizing the body, and only afterward does gut-associated lymphoid tissue (GALT) begin to develop the bacterial richness necessary to mucosal immunity.
But with almost one-third (32.8%) of American infants delivered via Cesarean section in 2012, per Centers for Disease Control and Prevention (CDC) numbers2, and with many mothers still unable to breastfeed as much as they’d like, some children may be missing an opportunity to maximize their microbial diversity. As evidence, a 2013 study3 found that infants delivered by Cesarean had especially low levels of bacterial richness and diversity at four months, while formula-fed infants displayed not only decreased species richness but an overrepresentation of Clostridium difficile—setting the stage for C. difficile-associated illnesses.
Such findings make it worth asking whether probiotics might set these infants on a bacterially richer start. One 2013 meta-analysis4 of 25 studies involving some 4,031 children found that not only did probiotic administration lower total levels of immunoglobulin E (IgE), an antibody that triggers allergic reactions, but that the reduction grew stronger with longer probiotic follow-up. The analysis also showed that probiotics significantly reduced the risk of atopic sensitization when administered both prenatally and following delivery.
On the matter of attenuating symptoms of asthma and wheeze, probiotics proved less effective—a result arrived at not just in the aforementioned meta-analysis but in another5 published the same year in British Medical Journal. Nevertheless, Brown is quick to note that “there’s some really wonderful work” going on in the field, and he believes it’s time for major players in probiotic research to establish large studies that examine how probiotics—either administered directly or through the breast milk of a supplement-taking mom—affect the development of atopic diseases like eczema and asthma in Cesarean infants. “Are the outcomes better?” he asks. If they are, “That’s huge. That’s a big public health message.”
Antibiotics: Too Much of a Good Thing?
Another big public health issue concerns the consequences of widespread antibiotic use. While no one disputes the utility of these lifesaving drugs, antibiotics, by definition, lay waste to microbial diversity, and the costs go beyond a worrying increase in antibiotic resistance (more on that shortly) to encompass the general microbial imbalance known as dysbiosis and its attendant disturbances.
The effects of even routine antibiotic treatment can be stark. One small study published in the Proceedings of the National Academy of Sciences6 found “profound and rapid” changes in the distal gut microbiota of the three subjects after only three days’ treatment with ciprofloxacin. After one week, microbial populations had partially returned to normal, but as far as 10 months out, the final composition of all study subjects’ gut microbiomes differed from that at the start. And per the results of another study7, published in PLoS ONE, clarithromycin and metronidazole appeared to reduce numbers of Actinobacteria—normal constituents of the microbiome—dramatically and immediately following treatment. Four years after treatment, some subjects’ microbiomes remained “perturbed” and their levels of antibiotic resistance high.
While greater restraint in prescribing antibiotics might help reverse these trends, probiotic supplementation might offer another strategy. In one double-blind, placebo-controlled trial8 involving 30 patients undergoing a seven-day course of amoxicillin, metronidazole, and lansoprazole for Helicobacter pylori infection, researchers examined probiotics’ effect on the patients’ populations of facultative anaerobes—a category of bacteria that includes pathogens like Escherichia coli, Staphylococcus, Streptococcus, and Listeria species. Subjects randomized to receive a placebo along with the seven days of antibiotic therapy and for eight days thereafter exhibited elevated levels of facultative anaerobes 27 days out from the start of treatment. Those receiving a placebo on days one through seven followed by a Lactobacillus acidophilus and Bifidobacterium bifidum supplement on days eight through 15 saw their facultative anaerobe levels rise only for the first seven days and then drop significantly subsequently. And in patients who received the probiotic for 15 full days, levels of facultative anaerobes remained steady throughout. “From these results,” the study’s authors write, “it can be seen that probiotic supplementation modulates the response of the intestinal microflora to the effects of antibiotic therapy.”
Closing the Floodgates
That’s great news, but can probiotic supplementation modulate—if not outright reduce—the occurrence of antibiotic-associated diarrhea (AAD), which is a frequent and unpleasant side effect of antibiotic treatment? The pooled data from five meta-analyses9, 10, 11, 12, 13 published over the past dozen years indicate that, in fact, it can—by about 50%.
In children, to which AAD can be especially debilitating, one meta-analysis14 of 16 studies involving 3,342 children found the incidence of AAD among those receiving probiotics was roughly half that of the control group’s (9% versus 18%, respectively). And in another meta-analysis15 that looked specifically at the effect of probiotics strains like Saccharomyces boulardii, Lactobacillus GG, and L. acidophilus CL 1285 on C. difficile-associated diarrhea (CDAD) in 4,213 participants, supplementation reduced CDAD incidence by 64%. The authors calculated that probiotic prophylaxis would prevent 33 CDAD cases per 1,000 persons, assuming a population with median control group risk—a conclusion that they said provides “moderate quality evidence” for the prevention of CDAD.
All of this comes as little surprise to Brown, whose own conclusion—“and at this point it’s actually kind of a yawner”—is that “of course” people should take probiotics when prescribed antibiotics. “The data,” he says, “is pretty strong,” especially vis-à-vis preventing complications associated with C. difficile. Alas, prevention is “an area where FDA will not allow companies to make claims,” he notes, which shortchanges public health and, he feels, “is very unfortunate. The funny thing, though, is that if you talk to the average family doc or gastroenterologist, a lot of them are aware that if their patient goes on antibiotics, they’re going to recommend that they use a probiotic.”
Another intriguing area where Brown sees strong support for probiotics is in preventing upper respiratory tract infections (URTIs), which can sap valuable learning time from school-aged kids stuck at home with the sniffles. But here, too, supplement marketers best tread carefully, as “FDA, particularly in the area of pediatrics, has really frowned on claims that something helps prevent colds and flus in kids,” he says. Yet the agency may look more favorably upon the suggestion that a product decreases the number of days a child misses from school—especially if the evidence backs it up.
And a 2009 study16 published in Pediatrics does just that. More than 300 children aged three to five randomly received either a single probiotic (L. acidophilus), a probiotic combination (L. acidophilus NCFM plus Bifidobacterium animalis subspecies lactis Bi07), or a placebo daily for six months. Those on both the single-strain and combined probiotic regimens experienced fewer incidences and reduced duration of fever, coughing and rhinorrhea compared to the placebo, with those in the combination group seeing the greatest reductions in all parameters. Even better, both the single-strain and combination groups decreased antibiotic use by 68.4% and 84.2%, respectively, and cut absences from daycare significantly compared to the placebo.
While those results highlight probiotics’ promise in promoting URT health in children, adults can benefit from supplementation, too. In a study17 of 310 18- to 60-year-olds published last year in Clinical Nutrition, not only did the risk of contracting a URTI fall significantly among subjects supplementing with Bifidobacterium lactis BI-04 versus a placebo, but those in the supplement group took longer to get sick, as well. “So those are the areas we might be able to ‘plug into’ and that really lend themselves best to wellness outcomes,” Brown says.
Public Health Importance
The wellness case is similarly compelling in the relationship between probiotics and women’s urogenital health. We know that uropathogenic E. coliand species associated with bacterial vaginosis—Gardnerella vaginalis and Atopobium vaginae among them—form dense biofilms that foil both the immune response and some antibiotics. But an in vitro study18 published in 2011 showed Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 capable of working themselves into those biofilms and disrupting—even killing—some of the associated pathogens. By contrast, the antibiotic metronidazole poked holes in the biofilms without wiping out the illness-causing microbes.
Such findings merit note because urinary tract infections (UTIs) not only have a high recurrence rate but also pose negative implications for pregnancy. So it’s heartening to see studies like a 2011 randomized, double-blind, placebo-controlled trial19 involving 100 young-adult women treated for acute UTIs. The subjects received either vaginal capsules of Lactobacillus crispatus CTV-05 or a placebo daily for five days following UTI treatment and then once weekly for 10 weeks. At the end of the study, not only was the rate of culture-confirmed UTI 15% among the probiotic group compared to 27% for the placebo, but probiotic supplementation correlated with a high level of L. crispatus colonization and a signification reduction in UTI occurrence, as well.
As far as averting antibiotic resistance goes, probiotics show promise here, too. A 2012 randomized, double-blind, noninferiority trial20 assigned 252 postmenopausal women with at least three self-reported UTIs in the past year to receive either treatment with trimethoprim and sulfamethoxazole (TMP-SMX) or a probiotic combination of L. rhamnosus GR-1 and L. reuteri RC-14 daily. After 12 months, though the mean number of symptomatic UTIs and median time to recurrence were both lower in the antibiotic group than in the probiotic cohort, the antibiotic group’s resistance to both TMP-SMX and amoxicillin more than doubled, while antibiotic resistance in the probiotic group didn’t increase at all.
Results like these convince Brown that “it’s time to start communicating from a public health point of view” that probiotics are a valuable tool in promoting women’s urogenital health. Moreover, he adds, “We need some big machers in the public health arena to tell postmenopausal women with recurrent urinary tract infections—who, of course, are being followed by their physicians—that these strains may in fact be an alternative prevention that’s actually safer than antibiotic prophylaxis, which not only is destroying GI flora but is also creating antibiotic resistance.”
On the Horizon
And these are only the areas where probiotic evidence is fairly established. Researchers are shedding light on unexplored spokes of the gut-health wheel, “and one of them,” Brown says, “is improving your cardiovascular health and possibly even getting your blood pressure in a healthier range.” A randomized, double-blind, placebo-controlled trial21 with 127 subjects revealed that those receiving a L. reuteri NCIMB 30242 supplement experienced significant reductions relative to the placebo in LDL cholesterol, total cholesterol, high-sensitivity C-reactive protein, fibrinogen (a glycoprotein involved in blood clotting), and apoprotein B-100 (ApoB-100), a proatherogenic lipoprotein. Triglyceride and HDL cholesterol levels remained unchanged in the probiotic group, while levels of the antiatherogenic apoprotein ApoA-1 actually fell.
As for hypertension, a meta-analysis22 of nine parallel, randomized, placebo-controlled clinical trials (seven of which were double-blind) show that subjects consuming probiotics enjoyed a “modest” lowering of blood pressure, and mainly among those with blood pressures above 130/85 mm Hg and who took the probiotics for longer than eight weeks as a multistrain supplement with a potency exceeding 100 billion CFUs.
Another area that Brown continues to watch is the growing problem of metabolic syndrome, “which is one of those grey areas that’s technically prediabetic, but gets back to public health,” he says. “It’s a huge health problem in our country right now, and if we can show that [we can] keep the gut healthy through diet and possibly probiotic supplementation, then we might also show that not only are you able to digest your food better but you’re decreasing the metabolic syndrome risk, too.”
But wait: there’s more. Obesity, the “gut-brain axis” (see sidebar on page 64), even baldness—all show hints of a microbiota link. Which should make supplement marketers excited—but not excessively so. “The neat thing is that we’re actually addressing the microbiome,” Brown says. “The scary thing is that we have a tendency to take something and try to be the first person on the block with it, or to fast-forward things before we do the appropriate amount of safety work.”
Even setting aside safety, there’s the fundamental question of selecting the right strains to use in potential products, and Brown has compiled a checklist to set manufacturers on the right path. For starters, choose a strain that’s viable. That seems obvious, but some strains need to be specially developed to survive stomach acid and bile. Assuming they do, you’ll also want to ensure they actually adhere to the intestinal wall so they can exert their benefits.
It’s also important to avoid any translocation of probiotics across the gut and into the bloodstream, Brown adds, as that could possibly lead to sepsis in some compromised individuals. And given that helping to stem antibiotic resistance is a key probiotic calling card, chosen strains certainly shouldn’t contribute to it or otherwise inhibit antibiotic action. Finally, aside from clear and compelling clinical evidence of safety and efficacy, you’ll want a strain with the stability to pull through on the shelf for as long as the date on the package says it should.
Simple in theory; a bit tougher in practice. But Brown’s bullish on what’s in store. Lactobacillus and Bifidobacteria have been our go-to organisms for years, but they may not be the only good guys to choose from, he says. “Maybe there are 20 more out there. And that might be another interesting thing for companies to be thinking about.”
Axis of Wellness: Investigating the Microbiota-Gut-Brain Axis
In the 1990s, Donald J. Brown, a naturopathic physician and managing director of Natural Product Research Consultants (NPRC; Seattle, WA), was intrigued by the possibility of a relationship between chronic fatigue syndrome and the hypothalamic-pituitary-adrenal (HPA) axis, a complex neuroendocrine feedback loop responsible for regulating everything from stress levels to sex drive. Decades later, he’s still got his eye on a feedback loop with broad wellness potential, but this time the focus is the microbiota-gut-brain axis and its role in conditions like irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).
Researchers have long encountered a certain “disrupted communication” between the gut and the brain in IBS sufferers, with signals getting warped en route from the former to the latter and the result being poor gut motility, hypersensitivity, and pain. Brown notes, as well, that IBS patients all too often “just sort of ‘manage’ [their condition] because there aren’t really any treatments.” But one symptom many do seek help for is pain “because it’s affecting their quality of life.”
So what does this have to do with probiotics? It happens that a 2004 study23 of 57 patients with active IBD and 46 healthy controls found the microflora of the IBD patients to be significantly less diverse and lacking in normal anaerobic species compared to those of the healthy controls. And another study24 published in JAMA the same year proposed small-intestinal bacterial overgrowth (SIBO) as a causative factor in IBS and showed 75% improvement in IBS after eliminating the SIBO.
Taking the research to the next level, a 2009 meta-analysis25 of 14 randomized, double-blind, placebo-controlled trials found that all but one suggested a modest improvement in IBS symptoms thanks to probiotics, with seven of the trials showing significant reductions in abdominal pain. “So what this is telling us is that the brain is communicating with the GI tract in the presence of healthy bacteria, and the bacteria are probably playing a role in modulating and working in harmony” with the gut-brain axis, Brown says.
And, he adds, the fact that some of the communication appears to travel through the vagus nerve “may explain part of the reason why in functional bowel diseases like IBS we’re actually seeing that one of the key symptoms that seems to be affected by probiotic supplementation in some of these studies is pain.” The ramifications could point the way to relief for a lot of people desperate for it. And that, Brown says, is intriguing. “If we could bring that gestalt together and go from that out to all the different spokes on the wheel, that’s really fascinating.”
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- Beerepoot MA et al., “Lactobacilli vs antibiotics to prevent urinary tract infections: a randomized, double-blind, noninferiority trial in postmenopausal women,” Archives of Internal Medicine, vol. 172, no. 9 (May 14, 2012): 704-712
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