Benefits
Stress response and daily stress (1714 strain)
Tested as the 1714 strain. In 22 healthy men given placebo first and then 1 billion CFU/day for 4 weeks each, the probiotic blunted the rise in cortisol and anxiety during a cold-water stress test and lowered daily stress. A 40-person randomized trial saw brain-activity changes but no difference in felt stress, and two larger trials missed their main sleep and mood goals.
Abdominal comfort and bloating (35624 strain)
In 362 women with IBS, 4 weeks of strain 35624 at 100 million CFU/day eased abdominal discomfort, bloating and bowel habits more than placebo, but the lower and higher doses did not beat placebo. In 302 adults with bloating who were not under a doctor's care, 1 billion CFU/day did not ease symptom severity more than placebo, though bloating-free days rose.
Nasal comfort during pollen season (BB536 strain)
In 44 people with Japanese cedar pollen allergy, BB536 taken for 13 weeks of the pollen season led to fewer early dropouts for severe symptoms or medication and lower runny nose, blocked nose and overall symptom scores than placebo. This is one small trial run by researchers at Morinaga, the strain's maker.
Bowel regularity in older adults (BB536 strain)
In 80 older adults (mean age 78) with chronic constipation, 50 billion CFU/day of BB536 for 4 weeks did not beat placebo on the main constipation score (P = 0.074), but stool frequency improved more than on placebo. Several authors were from Morinaga, the strain's maker.
Upper respiratory immune support in children and older adults (BB536 strain)
Tested as the BB536 strain only. In 520 Malaysian preschoolers given 5 billion CFU/day or placebo for 10 months, the BB536 group had fewer respiratory illnesses and 46% shorter sore throats, but only the 219 fully compliant children were analysed, and diarrhoea did not change. In 27 elderly adults, fewer caught influenza or had fever than on placebo over 14 weeks. Morinaga, which makes BB536, co-authored both.
Mechanism of action
Gut-brain signaling (proposed)
How strain 1714 might affect stress is not settled. Researchers suspect signals from the gut to the brain through nerves, immune messengers and microbial products. Changes in EEG and MEG brain activity in 1714 trials suggest some effect on the brain, but the pathway has not been shown in people.
Human milk oligosaccharide use
The infantis subspecies carries a large gene cluster for breaking down human milk oligosaccharides, sugars in breast milk that the infant cannot digest. This helps explain why it thrives in the gut of breastfed babies.
Cross-feeding of butyrate producers
Bifidobacteria ferment fibers and other carbohydrates the body cannot digest. Their products, such as acetate and lactate, can be used by other colon bacteria that make butyrate, the main fuel for the cells lining the colon.
Clinical trials
Within-participant, placebo-controlled study. Participants took placebo for 4 weeks and then B. longum 1714 (1 billion CFU/day) for 4 weeks, in that fixed order, with a socially evaluated cold pressor stress test, cognitive tests and resting EEG after each phase. The strain's maker supplied the products. (Allen et al. 2016, Transl Psychiatry)
22 healthy men.
After the probiotic phase, the rise in cortisol and in anxiety during the stress test was smaller and daily reported stress was lower. The authors also saw subtle gains in a visuospatial memory task and changes in frontal EEG. The fixed order (placebo always first) and small size limit how much this shows.
Randomized, double-blind, placebo-controlled multicenter trial of encapsulated B. infantis 35624 (now classified as B. longum 35624) at 1 million, 100 million or 10 billion CFU/day for 4 weeks. (Whorwell et al. 2006, Am J Gastroenterol)
362 women with IBS recruited in primary care.
Only the 100 million CFU dose beat placebo on the main outcome, abdominal pain or discomfort, and on bloating, bowel dysfunction, incomplete evacuation, straining, gas and the composite score; global symptom relief beat 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.
Randomized, double-blind, placebo-controlled trial of B. longum BB536 during the cedar pollen season, run by researchers at Morinaga, the strain's maker. (Xiao et al. 2006, Clin Exp Allergy)
44 people with Japanese cedar pollinosis, 13 weeks.
Fewer people on BB536 dropped out early because of severe symptoms or allergy medication (P = 0.0057 vs placebo), and rhinorrhea, nasal blockage and composite symptom scores fell more than on placebo. BB536 suppressed the pollen-season rise in plasma TARC, a Th2-related chemokine, while cedar-pollen-specific IgE only tended to rise less.
Randomized, double-blind, placebo-controlled trial of BB536 (50 billion CFU once daily) for 4 weeks. (Takeda et al. 2023, Am J Gastroenterol)
80 adults (79 completed, mean age 77.9) diagnosed with chronic constipation in Japan.
The main outcome, the change in total constipation score versus placebo, was not significant (P = 0.074). Stool frequency improved more than on placebo (P = 0.008), and failure of evacuation tended to improve (P = 0.051). Few side effects were seen. Several authors were from Morinaga.