In preliminary and double-blind trials,^14,15 a probiotic supplement (in this case, a non-disease-causing strain of Escherichia coli) was effective at maintaining remission in people with UC. In a double-blind trial, a combination probiotic supplement containing Lactobacilli, Bifidobacteria, and a beneficial strain of Streptococcus has been shown to prevent pouchitis, a common complication of surgery for UC.¹⁶ People with chronic relapsing pouchitis received either 3 grams per day of the supplement or placebo for nine months. Eighty-five percent of those who took the supplement had no further episodes of pouchitis during the nine-month trial, whereas 100% of those receiving placebo had relapses within four months. Preliminary and double-blind research suggests that combination probiotic supplements may be effective at promoting recovery and preventing UC relapses as well.^17,18,19

In a preliminary trial, people with UC significantly improved on a sugar-free, low-allergen diet with additional nutritional supplementation that included a multivitamin-mineral supplement (2–6 tablets per day); a fish oil supplement (400 mg per day); borage oil (400 mg per day); flaxseed oil (400 mg per day); and a probiotic formula containing Lactobacillus acidophilus and other species of beneficial bacteria.²⁰ Some participants received slight variations of this regimen. Since so many different supplements were given and since the trial was not controlled, it is not possible to say which, if any, of the nutrients was responsible for the improvement observed by the researchers.

In double-blind research, diarrhea caused by Crohn’s disease has partially responded to supplementation with the beneficial bacterium Saccharomyces boulardii.²² Although the amount used in this trial, 250 mg taken three times per day, was helpful, as much as 500 mg taken four times per day has been administered in research successfully using Saccharomyces boulardii as a supplement with people suffering from other forms of diarrhea.²³

In a double-blind study of children aged 1 to 6 years, supplementation with Lactobacillus GG five days a week in milk for seven months reduced the incidence of cavities by 49%, compared with unsupplemented milk.²⁴ The amount of Lactobacillus added to the milk was 5 to 10 x 10⁵ CFU per ml.

According to preliminary reports, some people with recurrent canker sores may respond to topical and/or oral use of Lactobacillus acidophilus²⁶ and Lactobacillus bulgaricus.²⁷ However, a double-blind study found no effect of acidophilus bacteria on the healing time of canker sores.²⁸

Lactobacillus acidophilus (the friendly bacteria found in yogurt) produces acids that kill invading bacteria.⁴¹ The effective amount of acidophilus depends on the strain used, as well as the concentration of viable organisms. These and other friendly bacteria known as probiotics inhibit the growth of potentially infectious organisms (pathogens) by producing acids, hydrogen peroxide, and natural antibiotics called bacteriocins and microcins, by utilizing nutrients needed by pathogens, by occupying attachment sites on the gut wall that would otherwise be available to pathogens, and by stimulating immune attacks on pathogens. Infections that have been successfully prevented or treated with friendly bacteria include infectious diarrhea, vaginitis, and urinary tract infections.^42,43

There is increasing awareness of the importance of gut bacteria in regulating metabolism and inflammatory immune function, and growing evidence indicates a role for probiotics, as well as prebiotics (fibers that enhance growth of beneficial bacteria) and synbiotics (combinations of pro- and prebiotics) in preventing and treating metabolic syndrome.⁵²

One placebo-controlled trial compared the effects of a multi-strain probiotic supplement and an inulin-based synbiotic supplement to placebo in 120 participants with pre-diabetes. Both the probiotic and synbiotic supplements reduced the prevalence of metabolic syndrome more effectively than placebo.⁵³ A meta-analysis was performed using data from nine randomized controlled trials investigating the use of probiotics in subjects with metabolic syndrome. The trials used different species of lactobacilli and bifidobacteria, at doses ≥ 6.5 billion colony forming units (CFUs), and lasted three to 12 weeks. Five of the trials reported small but statistically significant positive findings with regard to metabolic syndrome parameters such as body-mass index (BMI), blood glucose levels, and lipid metabolism.⁵⁴ In addition, certain probiotic strains appear to improve gut microbiome composition and reduce blood levels of inflammatory markers in people with metabolic syndrome.^55,56 More research is needed to identify specific strains, optimal doses, and duration of treatment needed for probiotics to improve metabolic health.

In a double-blind study of infants, supplementation of a standard milk-based formula with probiotic organisms (Bifidobacterium lactis and Streptococcus thermophilus) significantly reduced the frequency of colic, compared with the same formula without the probiotics.⁶³ Another double-blind study found that the probiotic preparation, Lactobacillus reuteri DSM 17938, was an effective treatment for colic in exclusively breast-fed infants.⁶⁴ In another study, L.reuteri DSM 17938 taken once a day was significantly more effective than simethicone, a drug frequently used to treat colic.⁶⁵ Other double-blind research has confirmed the benefit of probiotics (particularly L.reuteri DSM 17938) in infants with colic.⁶⁶⁶⁷⁶⁸

Lactobacillus acidophilus products are often used by people with candidiasis in an attempt to re-establish proper intestinal flora. Acidophilus produces natural factors that prevent the overgrowth of the yeast.^69,70 Although there are no human trials, supplementation of acidophilus to immune-deficient mice infected with C. albicans produced positive effects on immune function and reduced the number of Candida colonies.⁷¹ The typical amount of acidophilus taken as a supplement is 1–10 billion live bacteria daily. Amounts exceeding this may induce mild gastrointestinal disturbances, while smaller amounts may not be able to sufficiently colonize the gastrointestinal tract.

In a double-blind trial, supplementation with a specific probiotic strain (Bifidobacterium longum strain BB536) during the pollen season significantly decreased symptoms such as sneezing, runny nose, nasal blockage, compared with a placebo.⁷³

Probiotics may be important in the control of food allergies because of their ability to improve digestion, by helping the intestinal tract control the absorption of food allergens and/or by changing immune system responses to foods.^74,75,76 One group of researchers has reported using probiotics to successfully treat infants with food allergies in two trials: a double-blind trial using Lactobacillus GG bacteria in infant formula, and a preliminary trial giving the same bacteria to nursing mothers.⁷⁷ Probiotics may also be important in non-allergy types of food intolerance caused by imbalances in the normal intestinal flora.⁷⁸

A double-blind trial reported that use of a hypoallergenic infant formula plus probiotics (500 million organisms of Lactobacillus GG bacteria per gram of formula, taken for one month) initially led to improvement in eczema symptoms in infants with suspected allergy to cow's milk.⁷⁹ However, by the end of two months, both the group receiving Lactobacillus GG and the placebo group had improved approximately the same amount. In the same report, a preliminary trial giving 20 billion lactobacilli twice per day to breast-feeding mothers led to significant improvement of their allergic infants’ eczema after one month. However, another double-blind trial found that Lactobacillus GG was no more effective than a placebo in infants with mild to moderate eczema.⁸⁰ In another double-blind trial, a different probiotic preparation (1 billion organisms of Lactobacillus fermentum VRI-033 PCC taken twice a day) reduced the severity of eczema in a group of young children with moderate or severe eczema.⁸¹Probiotics may reduce allergic reactions by improving digestion, by helping the intestinal tract control the absorption of food allergens, and/or by changing immune system responses.

Stress is understood to have a detrimental effect on the balance of intestinal bacteria,^83,84 but whether probiotic supplements improve the ability to handle stress is unknown. In a six-month preliminary trial, a multivitamin-mineral (MVM) supplement that also contained a blend of Lactobacillus acidophilus, Bifidobacterium bifidum, and Bifidobacterium longum was effective for improving scores on a stress questionnaire.⁸⁵ However, this improvement could have been a placebo effect or could have been due to the MVM component. Controlled research comparing MVM supplements with and without added probiotics is necessary to determine whether probiotics are helpful for treating stress.

Lactobacillus acidophilus products are often used by people with candidiasis in an attempt to re-establish proper intestinal flora. Acidophilus produces natural factors that prevent the overgrowth of the yeast.^86,87 Although there are no human trials, supplementation of acidophilus to immune-deficient mice infected with C. albicans produced positive effects on immune function and reduced the number of Candida colonies.⁸⁸ The typical amount of acidophilus taken as a supplement is 1–10 billion live bacteria daily. Amounts exceeding this may induce mild gastrointestinal disturbances, while smaller amounts may not be able to sufficiently colonize the gastrointestinal tract.