"I think that it's worth trying," Dr. Birgitta Evengard of the Karolinska Institutet in Stockholm, study co-author, told Reuters Health. Evengard said she recommends her patients with chronic fatigue syndrome try taking the probiotics tested in her study, and stop if they start feeling worse, but stick with it for 3 weeks if they feel better or if they don't notice an immediate effect.

Evidence is increasingly pointing toward the need for individualized treatment for chronic fatigue syndrome, the researcher noted. The cause of this condition, characterized by debilitating fatigue that doesn't get better with rest and may be worsened by physical or mental activity, remains unclear, although there is evidence that dysfunction in the neurohormonal system or the immune system could be involved.

Given that there is a close connection between the gut and the immune system, as well as the central nervous system, Evengard and her colleagues decided to test whether probiotics -- which can restore the normal balance of bacteria in the digestive system -- might help patients with chronic fatigue syndrome.

The researchers first observed 10 female and 5 male chronic fatigue syndrome patients who were not treated for 2 weeks. Next, the study participants took two deciliters of Cultura Dofilus Natural Yogurt, twice daily, for 4 weeks, and then followed them for an additional 4 weeks.

Six of the patients reported improvements in their symptoms, while one said symptoms got worse. Four of the women reported improvements in their physical health and two said their mental health had improved by the end of the study. One man reported improvement in physical health and one other man reported improved mental health.

"For some patients this was a dramatic difference," Evengard said, adding that the challenge for the future will be to figure out who will benefit from probiotics and who will not.

The wide range of response is not surprising, because of the complexity of chronic fatigue syndrome, Evengard noted. "Everything in this research is really going toward individualization of treatment, that's the trend of research in the chronic fatigue syndrome area today."

The maker of Cultura Dofilus Natural Yogurt, Arla Foods, helped fund the study, which also received support from The Stockholm County Council.

Milk-Free Acidophilus is a strain of Lactobacillus acidophilus, a symbiotic homo- fermentative, lactic-acid-producing bacteria. Since many people are vegetarian or cannot tolerate dairy products, Nature's Sunshine has replaced the milk in these acidophilus capsules with a soy protein and other natural, non-dairy nutrients. Each capsule contains a minimum of 100 million bacteria, freeze-dried to maintain viability. Each capsule is also enterically coated to ensure its release in the intestine, where the bacteria normally flourish. Acidophilus may also be used to make cultured milk.

Lactobacillus reuteri (L. Reuteri Chewable Tablets) occurs naturally in the intestinal flora of humans and other animals. Reuteri helps to strengthen the body's natural defenses against harmful bacteria and maintain equilibrium in the gastrointestinal tract as it repopulates friendly flora in the gut. This strain secretes reuterin, a substance with antimicrobial properties that helps suppress the growth of unfriendly microorganisms in the gut. L. Reuteri may be taken with Probiotic Eleven to accelerate the growth of other beneficial trains. It helps soothe an irritable bowel and is recommended for use after a round of antibiotics or cleansing.