Gut microbiota and vitamin D: a promising team in the fight against osteoporosis?

The link between osteoporosis and vitamin D is well established and the link between the gut microbiota and osteoporosis is receiving increasing attention. What about the relationship between the microbiota and vitamin D?

First study on potential link between microbiota, vitamin D, and severe osteoporosis

It all started with a simple clinical observation: patients with severe osteoporosis (SOP) have low plasma concentrations of 25(OH)D₃, which in turn is associated with increased gastrointestinal disorders.

A Chinese team thus hypothesized that the composition of the gut microbiota could affect intestinal absorption of vitamin D. To test this hypothesis, 18 patients with primary osteoporosis (OP) and 18 with severe osteoporosis (SOP) were given identical diets.  

Measurements of the patients’ plasma concentrations of cholecalciferol (vitamin D3) and 25(OH)D₃, together with an analysis of their gut microbiota composition, produced promising results.

More diverse microbiota in SOP patients

A diverse microbiota is usually a sign of good health. However, this is not the case for osteoporosis and vitamin D metabolism. Indeed, it has already been shown that a diverse microbiota is associated with reduced bone mass (sidenote: Xu Z, Xie Z, Sun J, et al. Gut Microbiome Reveals Specific Dysbiosis in Primary Osteoporosis. Front Cell Infect Microbiol. 2020 Apr 21;10:160.Wang J, Wang Y, Gao W, Wang B, Zhao H, Zeng Y, Ji Y, Hao D
Wang J, Wang Y, Gao W, et al. Diversity analysis of gut microbiota in osteoporosis and osteopenia patients. PeerJ. 2017 Jun 15;5:e3450.  ) . This study has shown that SOP patients have a more diverse microbiota than OP patients and reduced levels of Bifidobacterium, bacteria involved in the intestinal absorption of certain fats and fat-soluble vitamins. On the other hand, Firmicutes were more abundant in the SOP patients than in the OP patients. A high Firmicutes/Bacteroidetes ratio is a potential indicator of dysbiosis. This may explain in part why the SOP patients suffered from more severe gastrointestinal symptoms.

Microbiota involved in intestinal absorption of vitamin D

Concentrations of cholecalciferol and 25(OH)D₃ in the blood were positively correlated, with plasma levels of both substances lower in the SOP patients. Since the meals provided to both groups were identical, circulating concentrations of 25(OH)D₃ therefore depended on the amount of cholecalciferol absorbed by the gut, which may be influenced by the gut microbiota. 

The differences in gut microbiota composition associated with low blood concentrations of 25(OH)D₃ in SOP patients suggest that certain gut bacteria are involved in the intestinal absorption of vitamin D, which may in turn influence the deterioration of OP to SOP.