Probiotics Gaining Recognition
Probiotics--dietary supplements containing live microorganisms that are consumed for their purported health benefits--are used widely in parts of Europe and Asia but have not caught on with consumers in North America. ``But they will,'' predicts Canadian probiotic proponent Gregor Reid. He says that microbiologists are needed to help assure that legitimate probiotic products reach the marketplace.
Experts claim that live microorganisms contained in probiotics help to heal or prevent illness by pitting these good microbes against disease-causing organisms, according to Reid, who is associate scientific director of the Lawson Research Institute and professor at the University of Western Ontario in London, Ontario, Canada. However, he says, ``not many'' of these claims are backed by ``good science.''
Scientific ambiguity has not kept probiotics from gaining popularity in some circles. In Japan, for example, about 10% of the population regularly consume Yakult, a dairy drink supplemented with a specific Lactobacillus strain. The French prefer probiotic yogurts and spend $300 million on them yearly. In Finland, fermented milk containing Lactobacillus acidophilus GG is popular. Dannon in the United States introduced Actimel, a dairy beverage containing L. casei, with a label that reads, ``Helps fortify your body's natural defenses.''
However, many of the yogurt and buttermilk products available commercially in the United States cannot be considered probiotics. The two key criteria qualifying such foods as probiotics are that they provide a functional health benefit and contain live cultures when eaten. Even though lactobacilli and streptococci are used in making regular yogurt and buttermilk, they may not be alive when eaten or strains used may not have a proven benefit. And, of course, some products sold as probiotics may not have any proof of being medically beneficial.
Reid and his collaborators in the United States and Finland are attempting to build a more comprehensive scientific base for evaluating such products. In the September 1999 issue of Applied and Environmental Microbiology, they present seven characteristics for a product to be considered an effective probiotic, including the ability to adhere to cells, coaggregate, and form a normal flora, and production of substances to prevent the growth of pathogens.
As part of this scientific base-building effort, Reid and his group surveyed hundreds of studies describing the effectiveness of Lactobacillus probiotics and concluded that only seven of the many strains now being incorporated into commercial products meet their proposed criteria. Of those seven strains, five of them--L. rhamnosus GG, L. acidophilus NCFM®, L. casei Shirota, L. casei CRL431, and L. reuteri MM53--are offered to consumers to help in maintaining intestinal health. For instance, these Lactobacillus strains are believed to reduce diarrhea caused by lactose intolerance or by rotavirus infections. The two other strains, L. rhamnosus GR-1 and L. fermentum RC-14, are believed to promote urogenital health.
In his own research, Reid finds that topical application of L. rhamnosus GR-1 reduces the incidence of recurring urinary tract infections in women. For example, in one study, use of a topical probiotic reduced infectious episodes from 6.0 per patient per year to 1.6 per patient per year. The supplement also raises by as much as two-fold the Lactobacillus viable counts in the vagina compared with pretrial levels, according to reports he published several years ago. Women who participated in the clinical trials were provided with laboratory-grown lactobacilli which had been freeze-dried and were encapsulated in gelatin. Capsules in the form of vaginal suppositories were administered on a weekly basis.
Reid looks upon such probiotics as a potential adjunct to mainstream medical approaches to treating such infections. ``Recurrent urinary tract infections are treated actively with antibiotics, and the rapid and worrisome increase in bacterial resistance means that we have to look at probiotics as another option,'' he says. Additional clinical trials beginning in October 1999 will test the effectiveness of an orally administered L. rhamnosus GR-1-based probiotic supplement in a similar population group.
Certain Lactobacillus strains tend to populate the healthy vagina. When disrupted by an overgrowth of Gardnerella vaginales, mycoplasmas, and anaerobes, bacterial vaginosis occurs. Bacterial vaginosis increases the risk for miscarriage, preterm delivery of low-birth-weight infants, endometriosis, and sexually transmitted diseases, including AIDS. Probiotics hold the potential to recolonize the normal microbial flora to prevent bacterial vaginosis.
``There's growing interest here [in the United States] in probiotics, inspired by increasingly health-conscious consumers,'' says microbiologist Mary Ellen Sanders, owner of Dairy and Food Culture Technologies in Littleton, Colo., and an adjunct research professor at the California Polytechnic State University in San Luis Obispo. In a forthcoming review in Food Technology, Sanders summarizes established evidence from human and animal studies that probiotic bacteria aid digestion, promote resistance to enteric pathogens, reduce the risk of colon cancer, modulate the immune system, and ward off urogenital infections. Other researchers have reported that consumption of probiotics is associated with reducing cholesterol or diarrhea (ASM News, September 1996, p. 456).
Preliminary evidence suggests that probiotics may also prevent allergies, lower blood lipids and blood pressure, and prevent Helicobacter pylori infection. About 20 species and strains of Lactobacillus and Bifidobacterium appear to merit probiotic status, according to Sanders.
For example, Sanders consulted with researchers at the American Health Foundation in Valhalla, N.Y., who demonstrated that L. acidophilus NCFM® fed to rats inhibits development of preneoplastic lesions in the colon. The probiotic also reduces the activity of the enzyme beta-glucuronidase, which seems to play a role in carcinogenesis, according to Bandura Reddy and colleagues at the American Health Foundation.
However, such findings do not prove that probiotics make a difference in the incidence of colon tumors in humans. Questions about the influence of probiotics on colon tumor incidence in humans can be addressed by human intervention trials and more information about mechanisms of action of probiotics. ``We don't have a good sense of the bottom-line influence of probiotics on human health,'' cautions Sanders.
In addition, whether a specific probiotic bacterium will have a beneficial effect on health cannot be guaranteed from knowing its genus and species. ``There's a clear need to validate strains,'' says Sanders. Head-to-head comparisons of different strains are rarely done, and many products sold as probiotic supplements contain strains with no proven clinical value. Despite these limitations, probiotics may offer low-cost, low-risk alternatives to antibiotics against emerging pathogens with enhanced virulence and antibiotic resistance, Sanders says.
Consumers are not the only ones becoming aware of probiotics. At least three scientific monographs on the topic were published in 1999: (i) Probiotics: A Critical Review by Gerald Tannock, Horizon Scientific Press; (ii) Biotherapeutic Agents and Infectious Disease by Gary Elmer, Humana Press; and (iii) Handbook of Probiotics by Y. K. Lee, John Wiley & Sons.
``Five to ten years ago, no one cared about good bugs,'' says Reid. ``If you didn't study a pathogen, there wasn't any grant money.'' Indeed, most of the published research about Lactobacillus-based probiotics comes from dairy scientists, some of whom are sequencing the L. acidophilus chromosome to learn more about probiotic functionality and mechanisms of action. ``There's still a lot we don't know,'' says Reid. He says that microbiologists can play a major role in isolating and testing mechanisms of action of probiotic strains, investigating their role in health maintenance, and packaging them into reliable products for human use.
Carol Potera is a freelance science writer based in Great Falls, Mont.