Benefits
Abdominal comfort and bloating in one dose-ranging capsule trial
In a 4-week trial in 362 women with IBS, capsules of strain 35624 at 100 million CFU eased abdominal pain, bloating and other bowel symptoms more than placebo, but the 1 million and 10 billion doses did not, and a pooled analysis did not confirm a benefit for the strain alone. A trial of 1 billion CFU a day in adults who had not seen a doctor found no difference from placebo in symptom severity.
Abdominal pain and bloating scores in an earlier milk drink trial
In an 8-week trial in 77 people with IBS, strain 35624 at 10 billion live cells a day in a malted milk drink lowered abdominal pain, bloating and bowel movement difficulty scores more than the plain drink in most weeks. The drink form and dose differ from the capsule sold, and the trial had about two dozen people per arm.
What pooled analyses of the strain on its own found
Two pooled analyses of placebo-controlled trials of strain 35624 on its own reached different answers. The first found no significant change in abdominal pain, bloating or bowel habit satisfaction. A newer one, pooling three trials, found less abdominal pain, straining and overall symptoms, but no clear change in bloating, urgency, gas or incomplete evacuation.
Symptom scores in an open-label study without a placebo group
In an open-label study, 233 adults with IBS took one 1 billion CFU capsule of strain 35624 daily for 30 days and had lower symptom severity and better quality of life scores than at the start. With no placebo group and no randomization, and with support from Biocodex, it cannot show that the capsule caused the change.
Lower blood C-reactive protein than placebo in two patient groups
In placebo-controlled trials of 6 to 8 weeks, adults with chronic fatigue syndrome (48) or psoriasis (26) taking 10 billion CFU of strain 35624 daily had lower blood CRP than those on placebo. A third group with ulcerative colitis stayed on mesalamine. These are blood markers, not symptom results, from a team employed by or consulting for Alimentary Health Ltd.
Results apply to strain 35624, not to generic B. infantis
Every study on this page tested strain 35624 (now named B. longum 35624). Its results cannot be assumed for other B. infantis or B. longum strains, and the capsule trial showed that even this strain helped at one dose but not at two others.
Mechanism of action
Strain-specific immune activity
The authors of the main capsule trial note that probiotic properties such as immune activity are unique to a particular strain, so findings for 35624 do not carry over to other strains of the same species.
Gut-immune axis systemic modulation
In the milk drink trial, an abnormal IL-10/IL-12 ratio at baseline normalized with this strain only, and in small placebo-controlled trials outside IBS blood CRP fell more than with placebo. Only the milk drink trial measured a marker alongside symptoms, and that link does not prove a cause.
Visceral antinociception
In rats given the strain by mouth for 14 days, pain behaviors during colorectal distension fell in both a normal and a pain-sensitive rat strain, while two other probiotics had no such effect. This is animal work and has not been shown to explain the human results.
Transient presence in the gut while taken
In an 8-week trial, fecal levels of strain 35624 DNA rose while capsules were taken and fell toward baseline once dosing stopped, so presence was transient. Whether the bacteria in stool were alive was not checked by culture.
Narrow dose window, and higher is not better
One trial found benefit at 100 million CFU and no benefit at either 1 million or 10 billion CFU. The trial report noted that the 10 billion CFU capsules had significant formulation problems, so calling this a proven hormesis or U-shaped curve goes further than the data allow. A higher CFU count is not automatically better here, and a separate trial of 1 billion CFU a day found no difference from placebo in symptom severity in adults who had not seen a doctor for their symptoms.
Clinical trials
Multicenter, double-blind, randomized, placebo-controlled trial of strain 35624 capsules. Doses are reported as 1 x 10^6, 1 x 10^8 or 1 x 10^10 cfu; the abstract states cfu/mL, the full text could not be read to confirm the count per capsule, and a later review lists the effective arm as 10^8 cells a day. Its matching registry entry, NCT00135031 (same design, 362 women), lists Procter & Gamble as lead sponsor and Alimentary Health Ltd as collaborator. (Whorwell et al. 2006, Am J Gastroenterol)
362 women with IBS of any bowel habit subtype, recruited from primary care, randomized to one of three doses or placebo for 4 weeks.
Only the 100 million (1 x 10^8) dose beat placebo and the other doses on abdominal pain (the primary outcome), the composite score, bloating, bowel dysfunction, incomplete evacuation, straining and passage of gas; global symptom relief exceeded placebo by more than 20%. The 1 million and 10 billion doses did not differ from placebo, and the 10 billion dose had formulation problems. No significant adverse events were recorded.
Randomized, placebo-controlled trial with three arms over 8 weeks: strain 35624 or Lactobacillus salivarius UCC4331, each 1 x 10^10 live cells in a malted milk drink, or the plain drink as placebo. (O'Mahony et al. 2005, Gastroenterology)
77 people with IBS (a later review lists 22 on this strain and 22 on placebo).
Versus placebo, the strain 35624 group had larger falls in every symptom score except bowel movement frequency and consistency; abdominal pain or discomfort, bloating or distention and bowel movement difficulty were significantly lower in most weeks. An abnormal IL-10 to IL-12 ratio at baseline normalized with this strain only.
Ten-center, double-blind, randomized, placebo-controlled parallel trial: 2-week placebo run-in, then 4 weeks of strain 35624 at 1 x 10^9 cfu a day or placebo. End-of-study severity of abdominal discomfort and bloating did not differ from placebo (P>0.3); bloating-free days were more frequent with the probiotic (P<0.05). One author was affiliated with Procter & Gamble. (Ringel-Kulka et al. 2017, Am J Gastroenterol)
302 adults recruited by advertisement who had recurring abdominal discomfort for at least 3 months and had not seen a doctor or taken prescribed medication for it in the past year; 275 gave evaluable data.
Both groups improved over the 4 weeks, and mean symptom severity at the end did not differ between the strain and placebo. The authors point to a high placebo response in this population.
Randomized, placebo-controlled comparison in IBS patients plus an open group of healthy adults on the capsule; fecal microbiota and IBS symptoms were secondary outcomes, and no effect on IBS symptoms was observed. A later review lists the dose as 1 x 10^9 cells a day. Two of the three authors were from Procter & Gamble, and viability in feces was not confirmed by culture. (Charbonneau et al. 2013, Gut Microbes)
76 patients randomized to the capsule (39) or placebo (37), plus 41 healthy adults taking the capsule.
Fecal levels of the strain rose versus placebo, were similar in the healthy adults, and fell toward baseline once dosing stopped. Ten other fecal taxa changed little, and symptoms did not change versus placebo.
Three separate randomized, double-blind, placebo-controlled interventions using sachets of 1 x 10^10 CFU strain 35624 or 5 g maltodextrin daily for 6 to 8 weeks, plus 22 healthy adults. The ulcerative colitis patients stayed on mesalamine throughout. Three authors were employees of Alimentary Health Ltd and four were consultants to it. (Groeger et al. 2013, Gut Microbes)
Adults with chronic fatigue syndrome (48), psoriasis (26) or ulcerative colitis (22), plus 22 healthy adults.
Plasma CRP fell more than with placebo in all three patient groups, and TNF-alpha fell more than with placebo in the chronic fatigue and psoriasis groups. IL-6 differences versus placebo in the colitis and chronic fatigue groups fell just short of significance (P=0.057 and P=0.054). In healthy adults, stimulated TNF-alpha and IL-6 release by blood cells was lower than with placebo. These are marker results; the paper reports no symptom outcomes.
Prospective, open-label, multicenter observational study with no placebo group or randomization, in adults with Rome IV IBS. Supported by Biocodex, which paid both authors personal fees. (Sabaté et al. 2022, World J Gastroenterol)
233 adults (mean age 51.4, 71.2% women) seen by private practice gastroenterologists in France.
After 30 days of one 1 x 10^9 CFU capsule a day, the severity score fell from 303 to 208 and the quality of life score rose from 60.2 to 68.8 compared with baseline; 57% moved to a lower severity category or remission. Without a control group these changes cannot be attributed to the capsule.
Double-blind, placebo-controlled, matched two-group design over 6 weeks of training; B. longum 35624 at 1 billion CFU a day (8 on probiotic, 9 on placebo). Funded by a grant from Procter & Gamble; the authors declared no competing financial interests and state the funder had no role in design, analysis or writing. (Carbuhn et al. 2018, Sports (Basel))
17 NCAA Division I female swimmers.
No between-group differences in swim time trials, vertical jump, or blood and saliva markers. Sport recovery scores on a recovery-stress questionnaire were higher than placebo in weeks 5 and 6.