Researchers studied 90 women, 75 to 80 years old, all generally healthy but with low bone mineral density. They measured their bone density at the start of the study, and then randomly assigned them to a placebo or to two daily doses of freeze-dried Lactobacillus reuteri, an intestinal tract microbe that occurs naturally in many, but not all, people.
After one year, they measured the women’s bones again. The reduction in density in the shin bone was nearly half as large in women taking L. reuteri supplements as in those taking the placebo. Side effects, most commonly gastrointestinal symptoms, were similar in the treatment and placebo groups. The study is in the Journal of Internal Medicine.
The lead author, Dr. Anna G. Nilsson, said that why this happens is unclear. “Perhaps estrogens could be affected by probiotics,” she said, “and there is some discussion about calcium absorption, a change in the calcium regulating hormones.”
Dr. Nilsson, an associate professor at the University of Gothenburg in Sweden, said that it is not yet time to advise women to take probiotics. “This is the first study in humans,” she said. “We need confirmatory studies. And we’ve only studied one strain of L. reuteri, the type used in animal studies.”