Milk and osteoporosis — does drinking milk protect bones?

Aim of the study: Milk and milk product consumption is positively associated with bone mineral density (BMD). Emerging evidence suggests that fermented milk products (FMPs) may have specific beneficial effects on skeletal health.

Results: Daily yogurt or cheese consumption for less than 2 months reduced levels of bone resorption markers, but did not affect bone formation markers. Among the fermented milk products studied in postmenopausal women, only higher yogurt consumption was associated with a lower risk of hip fracture compared with low or no consumption. Daily cheese consumption may be associated with higher BMD T-scores, but the evidence was limited. Further, longer-term trials examining these relationships are needed.

Aim of the study: Cow's milk is often severely criticized as a cause of multiple health problems, including an increased risk of fractures. A close look at the scientific literature shows a striking contradiction.

Results: Several hypotheses have been offered to explain these findings, such as a deleterious effect of D-galactose, lactose intolerance, and acid overload. Epidemiological studies face many obstacles when seeking to detect effects of a single food, particularly the multiplicity of interactions among foods. Furthermore, reliable dietary intake data must be collected over prolonged periods, often long before the occurrence of a fracture, and defective recall may therefore introduce a major yet often unrecognized bias, particularly in populations where calcium deficiency is uncommon. To date, there is no conclusive evidence that we should modify our currently high level of consumption of cow's milk.

Aim of the study: Bone mineral mass, geometry and microstructure, hence determinants of fracture risk, result bone accrual during growth and bone loss later in life. Peak bone mass, which is reached by the end of the second decade of life, is mainly determined by genetic factors.

Results: Both nutrients are provided in dairy products, which accounts for 50-60% and 20-30% of the daily calcium and protein intakes, respectively. Children avoiding dairy products are at higher risk of fracture, as are adults or older individuals following a diet devoid of dairy products, like vegans. Various intervention trials have shown some beneficial effects of dairy products on bone capital accumulation during growth and on bone turnover in adults. In observational studies, dairy products intake, particularly the fermented ones, which also provide probiotics in addition to calcium, phosphorus and protein, appear to be associated with a lower risk of hip fracture.

Aim of the study: Osteoporotic or fragility fractures affect one in two women and one in five men who are older than 50. These events are associated with substantial morbidity, increased mortality, and an impaired quality of life.

Results: Consuming less than five servings per day of fruit and vegetables is associated with a higher hip fracture risk. Adherence to a Mediterranean diet or to a prudent diet is associated with a lower fracture risk. These various nutrients and dietary patterns influence gut microbiota composition or function, or both. The conclusions of this Review emphasise the importance of a balanced diet including minerals, protein, and fruit and vegetables for bone health and in the prevention of fragility fractures.

Aim of the study: Milk kefir has shown osteoprotective potential, but whether fermentation duration influences its effects remains unclear. This study evaluated the influence of fermentation time on milk kefir microbial composition and its effects on mandibular bone in glucocorticoid-induced osteoporotic rats.

Results: Microbial composition was assessed by 16S and 18S rRNA gene amplicon sequencing. Lactobacillus dominated the bacterial community, whereas Saccharomyces predominated among fungi, with no major changes across fermentation times. Prolonged fermentation (MK4 and MK7) significantly increased serum calcium, mandibular cortical thickness, interradicular bone area, collagen maturity, and fracture resistance. These findings indicate that prolonged fermentation enhances the osteoprotective effects of milk kefir, despite relative stability of the dominant microbial taxa, highlighting fermentation duration as an important factor in optimizing milk kefir for preserving mandibular bone under osteoporotic conditions.

Aim of the study: To investigate the effect of milk minerals on bone mineral density (BMD) and bone quality in growing rats and explore the underlying mechanisms related to calcium absorption, bone metabolism, and the gut-bone axis.

Results: Milk mineral exhibited non-inferior efficacy to CaCO3 in increasing femoral calcium content, enhancing BMD, and improving bone microarchitecture. Notably, the Medium group achieved comparable bone-protective effects to the CaCO3 group despite a 20.8% lower calcium content, which was accompanied by a relatively high calcium absorption rate (90.9% vs. 86.5%). With respect to serum markers, milk mineral maintained bone formation while suppressing bone resorption, resulting in a net anabolic state comparable to that of CaCO3. Milk mineral significantly upregulated the protein expression of renal CYP27B1 and intestinal calcium ion transporters, and increased serum IGF-I levels. Furthermore, milk mineral promoted the enrichment of certain specific gut microbial genera, which showed a significant positive correlation with IGF-I, bone calcium content and BMD.