Probiotics get a boost
Sellers of 'friendly' bacteria offer evidence to back claims.
Can a dose of bacteria a day keep the doctor away? Yes, according to a study of Swedish workers who took supplements containing microorganisms: those on the 'friendly' bacteria pills stayed home sick half as much as their colleagues taking a placebo. The findings lend support to claims that foods with live bacteria can boost the body's immune system.
In recent years, particularly in Europe and Japan, food companies have marketed an increasing number of probiotic products, which contain microorganisms that are supposed to be good for you.
Many yogurts, for example, are promoted as conferring health benefits because they contain live bacteria such as Lactobacillus and Bifidobacterium. Proponents of such supplements say that these microbes aid the bacteria and yeast that naturally reside in the human gut, improving digestion and helping to combat pathogens.
Enthusiasm about probiotics can be traced back to the turn of the twentieth century when the Russian scientist Elie Metchnikoff suggested that Bulgarian peasants lived longer because they consume fermented milk products. Current studies have found some evidence to support the idea that eating such foods has an effect, including elevating the number of protective 'CD4+' immune cells in the blood1.
But experts say there has been a lack of evidence to support the idea that probiotic supplements provide general protection against sickness.
Now, researchers from two Swedish companies involved in the development of probiotic products say they have more data to add to the debate.
Workers at a packaging plant received daily liquid doses of either a placebo or Lactobacillus reuteri, a bacteria that is cultured in some yogurts, for 80 days. While 23 of the 87 volunteers receiving a placebo reported sick during that period, only 10 out of the 94 volunteers that took the L. reuteri said they were ill. The results of the blind study appear in the journal Environmental Health2.
Anders Zachrisson, a scientist at the probiotics company BioGaia in Lund who led the research, adds that the average duration of sickness was slightly shorter for participants receiving the supplements. And in shift workers, he notes, the effect was particularly marked.
"It's a well established fact that shift workers have a compromised immune system and are more likely to get colds. The really dramatic finding in this study is that none of the shift workers [receiving probiotics] got sick at all," says Zachrisson.
Amy Brown, a nutritionist at the University of Hawaii at Manoa in Honolulu, says that the benefits of L. reuteri compared with the placebo are intriguing. But she adds that it is hard to tell exactly how big the effect was, because the researchers did not keep track of whether people took days off owing to illness or injury. There isn't any evidence that a broken leg, for example, will be much helped by supplements.
No one has seen such a general prophylactic effect before, says Mary Ellen Sanders of Dairy and Food Culture Technologies in Centennial, Colorado. Sanders has studied probiotic bacteria and currently consults food companies on the topic.
Sanders thinks this could alter who decides to take the supplements. "Today, most people take probiotics if they suffer from some type of gastrointestinal or vaginal malady. But evidence from these studies points to the role probiotics may play in keeping you healthy, not just helping with symptoms," she says.
- Valeur N., Engel P., Carbajal N., Connolly E. & Ladefoged K. Appl. Environ. Microbiol., 70. 1176 - 1181 (2004).
- Tubelius P., Stan V. & Zachrisson A. Environ. Health, 4. 25 (2005).