The effects of dairy products containing Lactobacillus bulgaricus and Streptococcus thermophilus on bone turnover biomarkers and bone mineral density: a pilot trial study

Background/objectives Low bone mineral density is a major public health concern that negatively affects quality of life. Dairy products fermented with Lactobacillus bulgaricus and Streptococcus thermophilus have been suggested to promote gut health, enhance calcium absorption, and suppress inflammatory cytokines related to bone turnover. However, the benefits of these fermented dairy products on bone health remain unclear. This study aimed to compare the effects of consuming dairy products with and without Lactobacillus bulgaricus and Streptococcus thermophilus on bone turnover biomarkers and bone mineral density. Methods A randomized controlled pilot trial was conducted in a total of 40 female participants, who were allocated to either a control group ( n = 20) receiving full-fat milk or an intervention group ( n = 20) receiving yogurt fermented with Lactobacillus bulgaricus and Streptococcus thermophilus . Both groups consumed products providing an equivalent calcium intake of 400 mg/day for 12 weeks. Blood samples were collected, and body composition and bone mineral density were assessed. Results At the endpoint, serum calcium levels in the intervention group were significantly higher than those in the control group ( p < 0.05). Alkaline phosphatase and parathyroid hormone levels were significantly reduced from baseline in both groups ( p < 0.05). Bone mineral density at the right arm, right leg, and pelvis was significantly increased from baseline in the intervention group ( p < 0.05); however, no significant between-group differences in bone mineral density were observed at the endpoint. Conclusion Although within-group improvements in bone mineral density were observed, no significant differences between groups were detected. These findings should be interpreted with caution due to the pilot nature of the study, and larger, adequately powered randomized controlled trials are warranted to confirm the effects on bone mineral density. Clinical Trial Registration Identifier: TCTR20250807006.