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LETTERS TO THE EDITOR |
Faculty of Pharmaceutical Sciences
University of British Columbia
4-1815 West 13th Avenue
Vancouver, British Columbia V6J 2H4
Canada
E-mail: jfalk{at}telus.net
Dear Sir:
In a recent issue of the Journal, Saavedra et al (1) reported on the safety and potential benefits resulting from the addition of the live probiotic bacteria Bifidobacterium lactis and Streptococcus thermophilus to infant formula. We agree that the rationale for the use of probiotics in infant formula is theoretically valid. The results of the study showed that infants fed formula containing live probiotic bacteria had a significantly lower frequency of colic or irritability and a lower frequency of antibiotic use than did infants who consumed standard formula. A number of issues cause us to question the validity and applicability of the reported results to clinical practice.
An exclusion criterion of the study was a breastfeeding frequency of 
3 times/d. It is well established that breastfeeding is a major contributor to the immunologic health of infants. Therefore, breastfeeding has the potential to act as a major confounder in this study. In a child consuming probiotic-supplemented formula who is also breastfed, it is possible that any advantages gained are due primarily to the benefits of breastfeeding alone. The 3 formula groups in the study were unbalanced in terms of the percentage of infants who were breastfeeding at study entry (high-supplement formula: 23%; low-supplement formula: 28%; and standard formula (placebo): 15%). Although it is unfortunate that randomization did not prevent this from occurring, it is questionable whether breastfeeding should have been permitted at all or whether the study population should have included formula-fed infants only.
A statistically significant difference between the standard and probiotic formula groups was the frequency of reported colic or irritability. The infants studied ranged in age from 3 to 24 mo (mean age: 7 mo). By definition, colic is a term used to describe frequent prolonged bouts of fussing, crying, and restlessness in an otherwise healthy infant that may persist into the second half of the first year of life, but tends to improve or disappear in most cases after 3–4 mo of age (2). Thus, it is difficult to interpret the reported decrease in colic or irritability in the probiotic-supplemented group as a direct consequence of the type of formula administered. It appears possible that those infants out of the colic phase (eg, infants >6 mo of age) would benefit from probiotic supplementation. A group of infants with a narrower, younger age range would have been a more appropriate group to study.
The frequency of antibiotic use was also found to be significantly different between the probiotic formula and the standard formula groups. The group with the lowest antibiotic use, the low-supplement group, averaged 2.47 d of antibiotic use per 100 subject days (95% CI: 2.11, 2.84), whereas the standard formula group averaged 3.60 d of antibiotic use per 100 subject days (95% CI: 3.17, 4.02). Although the difference was statistically significant, one could argue that a reduction of 1 d out of 100 d is not clinically significant.
This study offers insight into the use of infant formulas supplemented with probiotic bacteria and the challenges encountered in designing these trials. We feel that further study in this area is warranted before any changes to current practice take place as a result of the study's findings.
REFERENCES
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