A lactose dose of 25 to 50 g is given after an overnight fast. A rise in the hydrogen level of more than 20 parts per million (ppm) over baseline suggests hypolactasia.7 At a cutoff of 20 ppm, the test has a specificity of 90%. False positives may occur secondary to severe bacterial overgrowth of the small bowel, smoking, and aspirin use. False negative results are seen in persons receiving oral antibiotics or high colonic enemas, suffering severe diarrhea, or lacking bacterial flora.8
Another use of the breath hydrogen test is to measure the quantity of lactose malabsorbed. This theory was based on a study of lactulose in which ingested doses of 5, 10, or 20 g resulted in a linear increase in breath hydrogen along with the similar malabsorption patterns of lactulose and lactose.9
The purpose of our systematic review was to determine if probiotics have a positive effect in patients with lactose intolerance. We found no systematic reviews or meta-analyses in the Cochrane Database of Systematic Reviews or the Database of Reviews of Effectiveness (DARE).
Methods
Inclusion criteria
The clinical question researched was “Does the addition of probiotics to nonfermented dairy products decrease lactose intolerance at a single meal?” Inclusion criteria for review were studies that were randomized placebo-controlled clinical trials, that involved adults diagnosed with lactose intolerance via breath hydrogen >20 ppm above baseline after lactose consumption, that used probiotic supplementation in any form as the intervention, and that included the outcomes of symptoms or breath hydrogen test results.
Search strategy and assessment
Four authors (MD, KK, KL, JM) independently searched Medline and Allied and Complementary Medicine Database (AMED) for studies published between 1966 and December 2002. Four authors performed individual searches using the Medical Subject Heading (MeSH) terms 1) “lactose intolerance” and “Lactobacillus”; 2) “lactose intolerance” and “probiotics”; 3) “lactose intolerance” and “yogurt”; and 4) “diarrhea, bloating, abdominal pain” and “yogurt.” The search strategies for each member were documented, and the resulting published listings were combined.
The initial set of articles was pulled and references from those studies were searched. In addition, manufacturers of Lactobacillus supplements and authors identified with expertise in lactose intolerance were contacted by phone or e-mail in an effort to look for any unpublished or ongoing trials possibly missed in the initial search.
Each author independently assessed each of the selected articles for validity using the recommendations made by the Evidence-Based Medicine Working Group at McMaster University.10 These validity criteria included patient similarity, evidence of controls, randomization, allocation concealment, blinding, completion of follow-up, use of intention-to-treat, and similarity of intervention and control groups. The authors then met to discuss their assessment and clarify any article concerns. General agreement was reached, and there were no dissenting views.
Data extraction
A standardized data extraction form was developed by 1 author (FD) and each paper’s information was extracted by 1 of the other authors (KL) and verified by the final author (FD). The following data were extracted: number of treatment arms, types of treatment arms (including forms of probiotics), number of subjects per treatment arm, study design, data presentation, and results obtained.
No formal statistical procedures or tests were performed. Authors hoped that appropriate data could be collected from each paper so that a meta-analysis could be performed. However, the lack of standardized data presentation for breath hydrogen and symptom results made data pooling impossible.
Results
Medline and AMED searches yielded 75 clinical trials. The reference search from these studies gave an additional 15 trials. No studies were identified through manufacturer or expert author inquiries. From the master list of 90 studies, 22 met inclusion and exclusion criteria. Of the 22, 10 were consistent with our clinical question. Of these 10 articles used in the study, 8 were obtained from the Medline and AMED searches, and 2 were obtained from the references.
Of the 10 randomized placebo-controlled trials, sample sizes for probiotic treatment arms ranged from 5 (Dehkordi) to 20 (Lin & Yen). Probiotic arms varied in subtype, strain, and concentration. Most of the studies (9) used the Lactobacillus acidophilus subtype as the intervention. Four trials examined probiotics other than, or in addition to, L acidophilus (Dehkordi, Jiang, Lin & Yen, Lin & Savaiano). Dehkordi performed 2 experiments. The first experiment examined the additive of effect of Lactobacillus and Bifidobacterium longum. The second compared only Lactobacillus strains with control milk.
Lin & Savaiano in 1990 compared 3 Lactobacillus strains, each with 2 different concentrations, as well as the combination probiotic subtypes of Streptococcus thermophilus/Lactobacillus bulgaricus at 2 concentrations with the control milk.