"We know that inflammation in the gut can cause bone loss, though it's unclear exactly why," said Laura McCabe, professor of physiology and radiology, Michigan State University (MSU). "The neat thing we found is that a probiotic can enhance bone density."

Researchers fed mice Lactobacillus reuteri, a probiotic known to reduce inflammation, a sometimes harmful effect of the body's immune response to infection, the Journal of Cellular Physiology reports.

"Through food fermentation, we've been eating bacteria that we classify as probiotics for thousands of years," said co-author Robert Britton, associate professor of microbiology and molecular genetics at Michigan.

"There's evidence that this bacterium as a species has co-evolved with humans. It's indigenous to our intestinal tracts and is something that, if missing, might cause problems," Britton added, according to a Michigan statement.

In the study, the male mice showed a significant increase in bone density after four weeks of treatment.

There was no such effect when the researchers repeated the experiment with female mice, an anomaly they are now investigating.

By 2020, half of all Americans over 50 are expected to have low bone density or osteoporosis, according to the National Osteoporosis Foundation. About one in two women and one in four men over 50 will break a bone due to osteoporosis.