Supplements containing "good" bacteria can help some people with chronic fatigue syndrome feel better, but they may make others feel worse, report Swedish researchers who conducted a small study.

"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.

None of the authors reported any competing interests.