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Letter to the Editor |
Departments of Medicine and Community Health Sciences The University of Calgary Faculty of Medicine Health Sciences Center 3330 Hospital Drive NW Calgary, Alberta Canada E-mail: gvrosend{at}ucalgary.ca
Dear Sir:
Anderson et al (1) recently combined 8 studies sponsored by the Proctor and Gamble company, including 3 unpublished projects from 1994, in a meta-analysis. They excluded research regarding cholesterol lowering by psyllium in hypercholesterolemic adults if it did not meet narrow criteria regarding the dietary lead-in period, the dose of psyllium used, and the length of treatment. Studies in which psyllium was provided in a cereal were excluded. Reports that appear to otherwise meet their criteria but that had different industry sponsors were not included (2, 3). Furthermore, this report did not clarify the quality of the clinical trials included in the analysis (4).
The inclusion of unpublished data in meta-analyses is controversial. Authorities in the field believe that, at a minimum, all studies should undergo the same rigorous methodologic evaluation and that results should be presented with and without the unpublished material (5). This issue may be particularly important when reporting pooled data from research originating from a single industry sponsor, which raises the question of whether there are additional unpublished studies, not included, that failed to show a cholesterol-lowering effect of psyllium. The possibility of publication bias is an important concern in an area in which investigation is dominated by industry sponsorship (6). The inclusion of a funnel plot might have also alerted the reader to the potential for unpublished negative studies (7).
The accompanying editorial by Jenkins et al (8) raises an additional concern. In considering the difference in evaluating therapeutic foods as opposed to drugs, they contend that "a health claim must be related to a specific product based on the testing of that product or accompanying specific line of products. Competing companies wishing to make a specific product claim for a similar product would have to give evidence of efficacy of that product." This raises an untenable specter of endless repeated clinical trials sponsored by each company wishing to bring a product to market that is similar to those already marketed. Surely, the better strategy would be to demand standardization of food products in the performance of clinical trials so that there can be some generalizability of research findings. It should be possible, for example, to undertake research on psyllium, which is fairly generic and would allow for possible minor differences, rather than demand that research be specific to any individual company's psyllium product. Are there any scientific data showing that psyllium products differ significantly by manufacturer?
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