What Are Probiotics?
by Diseree lie MD
Probiotics are defined by the World Health Organization (WHO) as "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host."
Probiotics are found in the gastrointestinal tract or as components of foods and beverages.
They are different from prebiotics, which are complex carbohydrates (nondigestable, fermentable polysaccharides) that stimulate the growth and/or activity of beneficial bacteria already in the colon. Prebiotics may be considered precursors to probiotics, and their role has yet to be defined in larger clinical studies.
Probiotics and prebiotics may be combined in a single product called synbiotics.
Most probiotics are either Lactobacillus or Bifidobacterium and their various species and strains (for example, Lactobacillus acidophilus and Bifidobacterium bifidus).
Other common probiotics are yeasts -- for example, Saccharomyces boulardii.
Probiotics are believed to reinforce the integrity of the intestinal lining as a protective barrier to prevent invasion by pathogenic organisms, and they are purported to prevent harmful bacteria or yeast from breaching the gastrointestinal mucosa.
They have an effect on priming immunophysiologic regulation in the intestinal mucosal barrier and may exert clinical effects beyond the nutritional value of food.
This effect is the rationale for their efficacy in preventing infectious or other forms of diarrhea and for the treatment of allergic conditions.
Formulations of Probiotics
Probiotics are available as tablets, powder, capsules and can also be mixed into beverages such as yogurt, milk, or juice.
Many different forms are offered worldwide.
Bifidobacteria appear to be safe when used orally, including in those under 2 years and ill neonates.
For example, a combination probiotic consisting of Lactobacillus, Bifidobacteria, and Streptococcus salivarius, known as VSL#3, was used in children ages 1 to 16 years for up to a year.
For preventing diarrhea in children, 5-10 billion live Lactobacillus GG have been used twice daily as tablets. Doses of 10-100 billion live organisms are available in tablet form, and capsules of 3 grams are also available.
There is a body of evidence supporting the benefit of probiotics in diarrhea-associated diseases. Several probiotics (Saccharomyces boulardii and a mixture of L acidophilus and B bifidum) have shown efficacy for preventing traveler's diarrhea with a relative risk (RR) reduction of 15% (RR=0.85, P < .001).[8,9]
Probiotics have also been shown to benefit antibiotic-associated and pediatric infectious diarrhea, especially rotavirus-related diarrhea. Probiotics have been used for a variety of gastrointestinal disorders as well, including these clinically successful applications for conditions related to inflammatory bowel disease:
•Lactobacillus GG to maintain remission in those with ulcerative colitis;
•S boulardii in combination with mesalamine to prevent clinical relapse of Crohn's disease (it should be noted that a Cochrane review concluded that studies to date have been too small to draw conclusions about use of probiotics for Crohn's disease prophylaxis);
•VSL#3 for prophylaxis of pouchitis and improved quality of life following ileal pouch-anal anastomosis; and
•VSL #3 for prevention of recurrent pouchitis after antibiotic-induced remission in patients with a refractory form of this condition.
Probiotics have also been found to be helpful in diarrhea-predominant irritable bowel syndrome. For example, in a meta-analysis, the odds ratio (OR) in favor of active probiotic treatment over placebo in children for diarrhea was 0.39 (P < .001) for yeast and 0.34 (P < .01) for Lactobacilli.
Similarly, probiotics offer a possible way to prevent antibiotic-associated diarrhea. A randomized study using 100g of a drink containing Lactobacillus casei, Lactobacillus bulgaricus, and Streptococcus thermophilus taken twice daily for one week after a course of antibiotics reduced the incidence of antibiotic-associated diarrhea and Clostridium difficile-associated diarrhea.
Allergic diseases. Two Cochrane reviews looking at the prevention of allergic disease and food hypersensitivity in infants found positive evidence from studies using Lactobacillus rhamnosus in favor of eczema prevention but not treatment.
A few reviews found encouraging, but not strong, effects, for several species of Lactobacilli for atopic dermatitis; these reports were based on placebo-controlled, randomized studies, using the SCORing Atopic Dermatitis (SCORAD) index for assessment, with possibly greater effects in children who have cow's milk allergy.
As noted in other reviews, a benefit was more likely to be seen for the prevention of eczema than for improvement of existing eczema. Most of the studies showing benefit were small and limited in scope. Of interest, when mothers consumed probiotics during pregnancy (starting 2 to 4 weeks before delivery), the likelihood of atopic dermatitis in the child was reduced at 2 years by about 50% in one study, and the cumulative effect on prevention was still evident at 4 years.
However, there was no effect on respiratory allergy, immunoglobulin E (IgE) levels, or allergic sensitization in these children. When infants were given probiotics in the first 6 months of life, a similar reduction in incidence of atopic eczema at 2 and 4 years was noted in these 2 studies.
Another randomized controlled trial of infants 5 months and younger, however, showed no effect of probiotic supplementation with L rhamnosus compared with placebo in the form of a hydrolyzed whey-based formula on atopic dermatitis in children when given for 3 months.
Overall, while there is a sound theoretical basis for a benefit of using probiotics for allergic disease, there is currently insufficient data to recommend it for all allergic conditions. With that said, there is more evidence supporting its use in preventing atopic dermatitis in children than for other allergic or immune conditions.
Respiratory illnesses. Studies in teenagers and adults with established respiratory disease have failed to show symptom improvement in asthma or allergic rhinitis although quality of life was improved in 1 study.
Studies on the common cold in adults have shown a reduction in duration and severity but not the incidence of cold episodes with improved cytotoxic T and T- suppressor cell immune function.
When given in winter for at least 3 months, a combination of probiotics and vitamins and minerals reduced both the incidence and severity of common cold infections in adults with concomitant immune function improvement.
In children, a twice-daily dose of L acidophilus alone or in combination with Bifidobacterium compared with a placebo given over 6 months in winter was found to reduce:
•Antibiotic use by 68% (single strain) to 84% (strain combination);
•Absenteeism from day care due to respiratory infection by 32% (single strain) and 28% (strain combination); and
•Symptoms of cough, fever, and rhinorrhea by 28% to 60%.
These observations were confirmed in another study of 571 children attending day care centers that provided cow's milk with or without Lactobacillus GG for 7 months, and found a relative reduction in:
•Incidence of respiratory infection (17% reduction);
•Antibiotic use for infection (19% reduction); and
•Absence from day care due to illness (16% or 1-day difference; P = .03).