Practice recommendations

• Become familiar with the strains, concentrations, and preparations of probiotics most likely to be effective.

• Because a given individual may respond well to probiotics, suggest a trial of a probiotic supplement—perhaps conducting an n-of-1 trial for an objective assessment.

• If a trial of probiotic does not achieve desired results, advise the patient of the many other options to treat lactose intolerance.

Purpose: To assess the efficacy of oral probiotics in adults with lactose intolerance through a systematic review of its effects on symptoms and breath hydrogen tests, and whether adding probiotics to nonfermented dairy products decreases lactose intolerance at that meal.

Methods: We searched randomized controlled trials published between 1966 and December 2002. Databases in the search strategy included Medline and AMED. We reviewed references of clinical trials and contacted authors of major articles and manufacturers of probiotic commercial products. Quality assessment was based on the McMaster guides and was performed by 5 independent reviewers. Data extraction was performed by 2 reviewers.

Results: A master list of 90 articles was compiled. Ten articles met inclusion and exclusion criteria and were consistent with our clinical question. Of the 9 studies that measured breath hydrogen, 3 were positive, 3 were negative, and 3 had both positive and negative results. Of the 7 studies that measured symptoms, 1 yielded positive results, 5 were negative, and 1 had both positive and negative outcomes.

Conclusions: Probiotic supplementation in general did not alleviate the symptoms and signs of lactose intolerance in adults in this review. Some evidence suggests that specific strains, concentrations, and preparations are effective. Further clinical trials of specific strains and concentrations are necessary to delineate this potential therapeutic relationship.