Even though bone strength is determined by bone quantity and bone quality, most current osteoporosis interventions aim at improving bone quantity. Studies focussing on the gut microbiome have shown that altered commensal gut flora can influence bone quantity in addition to bone tissue quality. Given that most evidence supporting this comes from studies involving young, growing mice, a recent manuscript, published by Castaneda et al. in the June 2021 issue of Bone Reports, explored the impact of alterations to the constituents of the gut microbiome on bone strength in older mice, up to 24 months of age.
The study used retired breeder C57BL/6 male mice, from the age of 12 to 24 months; they were allocated to a high glycemic diet, low glycemic diet or low glycemic diet with antibiotics.
At the end of the treatment period, mechanical testing showed that whole bone strength was greater in the group fed high glycemic diet, and microCT analysis showed that this group had increased cortical area and thickness compared to mice on low glycemic diets. Unsurprisingly, gut microbiome composition of the low glycemic + antibiotics group was the most affected, with reduced overall diversity of microbiota species. In addition, this group also showed greatest alterations in bone tissue strength compared to the other two diet groups. This reduction is similar to bone tissue strength alterations reported previously in young adult mice with altered microbiome.
Authors concluded that gut dysbiosis in aged mice can cause reductions in bone strength that could not simply be attributed to altered bone geometry. Given the long-term impact of antibiotics on the baseline diversity of the gut microbiota, this study provides evidence why the use of any antibiotic should always be carefully considered.