Do probiotics reduce adult lactose intolerance? A systematic review
Trials using L bulgaricus (Lin, Savaiano, and Lin and Yen) may have isolated a therapeutic subtype other than acidophilus. Lin, Savaiano found that 1 of 2 L bulgaricus/S thermophilus combinations significantly reduced symptoms. Whether this difference may be attributed to 1 of the 2 subtypes or their combination can only be speculated.
Additionally, Lin and Yen found that both strains of L bulgaricus 449 at concentrations of 108 and 109 significantly improved breath hydrogen and symptom scores. This positive association may be related to any or all of its subtype, strain, or concentration. Also in that study, both probiotic subtypes of L acidophilus and L bulgaricus at concentrations of 109 significantly reduce symptoms. Unfortunately, there was not enough specific information on strain characteristics to draw any firm conclusions. In future studies, careful attention to bacterial characteristics may provide a definitive answer to our questions.
The lack of standardized data presentation for breath hydrogen and symptoms in these 10 trials was a limitation. Some papers had only graphs of mean breath hydrogen, some showed differences from baseline, and some showed various summary statistics of breath hydrogen over different time periods. There was no standard objective measure of symptoms such as a Likert scale. Instead, symptoms were expressed in various ways (number of instances, scoring systems, or sole mention in text format). For these reasons, a meta-analysis could not be performed. This review could be further criticized because authors were not directly contacted for raw data for a potential meta-analysis.
Recommendations from this review
Several recommendations can be extracted from the results of this review.
First, probiotics in general do not reduce lactose intolerance (SOR: A). However, some evidence suggests that specific strains and concentrations are effective (SOR: B).
Second, there were enough positive treatment arms to suggest that some individuals will, for unknown reasons, have their symptoms eliminated or reduced with probiotics (SOR: B). It is reasonable, therefore, for clinicians to simply tell patients to “try it.” For a more objective analysis, an n-of-1 trial could be used.21 Clinicians will have to keep in mind that many people presumed to have lactose intolerance do not meet standard diagnostic criteria when objectively assessed.
Third, several strategies are available to lactose-intolerant persons (SOR: C). Yogurt, lactase enzymes, lactose-free or lactose-reduced products, specific foods, and probiotics selective for strain, concentration, and preparation are all supported by evidence. Onwulata compared results of probiotic milk, lactase tablets plus milk, hydrolyzed lactose milk, and yogurt with that of whole milk. Only yogurt and hydrolyzed lactose milk yielded significantly lower breath hydrogen results. Six of 10 patients reported symptoms with probiotic milk, 3 of 10 with lactase tablets, 1 of 10 with hydrolyzed milk, and no symptoms were reported with yogurt.
Dehkordi showed that probiotic milk had no effect on breath hydrogen results, but his treatment arm of cornflakes with whole milk did significantly affect results. McDonough found that when sweet acidophilus milk was sonicated to release intracellular lactase from the bacterial cells, a significant change in breath hydrogen resulted. Unfortunately, neither Dehkordi nor McDonough measured symptoms in their studies to specify patient-oriented outcomes.
Fourth, many individuals with symptoms of lactose intolerance do not meet the definition of diagnosis as measured by breath hydrogen testing (SOR: B). All clinical trials in this review declined subject enrollment if lactose intolerance symptoms were unconfirmed by breath hydrogen testing, thereby accepting only true positives.
There are several reasons why probiotic supplementation may be superior to commercial lactase supplementation. Patients have varied responses to lactase supplementation with meals, and different preparations may be more or less effective for the same quantity of lactose ingested.22 Also, as mentioned earlier, other research supports the role of probiotics in preventing diarrheal illness, treating irritable bowel syndrome and inflammatory bowel disease, and possibly benefiting persons with atopic disease. Finally, if lactase-producing probiotics are clinically effective and can also adhere to the intestinal lining, patients may experience prolonged reduction or remission of symptoms without the need to ingest any tablets with meals.
Two of the 10 studies (Newcomer, Kim) examined long-term probiotic use for 1 and 2 weeks, respectively. Newcomer measured only symptoms, showing no significant difference between L acidophilus milk and unaltered milk. Kim found that 2 of 3 L acidophilus concentrations significantly decreased breath hydrogen results, but the study did not measure symptoms. We can infer a negative patient-oriented outcome of long-term probiotic intervention based on these 2 trials. However, this domain of chronic probiotic use to reduce lactose intolerance would benefit from additional studies for comparison.
