Joint association of milk intake and blood 25(OH)D levels with fracture risk in postmenopausal women: 20-year follow-up data from the Japanese Population-Based Osteoporosis cohort study.

UNLABELLED: The associations between milk intake frequency and fracture risk in groups categorized by 25(OH)D levels were investigated using 20-year follow-up data. A significant association was observed only among women with 25(OH)D levels < 15 ng/mL. The measurement of blood 25(OH)D levels should be prioritized for individuals with low milk intake.

PURPOSE: To investigate the association between milk intake frequency and fracture risk in groups based on blood 25(OH)D levels.

METHODS

This secondary analysis of a prospective cohort study included data from 1209 postmenopausal Japanese women aged ≥ 50 years. Baseline milk intake frequency was obtained using a questionnaire. Blood 25(OH)D levels were measured using a competitive protein-binding assay. Information on fracture events was obtained from face-to-face interviews through follow-up or supplemental mail surveys.

RESULTS

Over a median follow-up period of 16.1 years (total: 17,427 person-years), 358 and 238 women sustained at least one clinical and osteoporotic fracture, respectively. The proportions of participants with milk intake < 1 glass/day and those with 25(OH)D levels < 15 ng/mL were 31.9% and 21.6%, respectively. In univariate Cox proportional hazard analyses, a 25(OH)D level < 15 ng/mL and a milk intake of < 1 glass/day were associated with an increased risk of clinical and osteoporotic fractures. Among participants with 25(OH)D levels < 15 ng/mL, the adjusted hazard ratios for milk intake < 1 glass/day compared to ≥ 1 glass/day were 1.99 (95% confidence interval: 1.32-2.99) and 2.11 (1.28-3.47) for clinical and osteoporotic fractures, respectively. In contrast, the HRs were not significant among those with 25(OH)D levels ≥ 15 ng/mL.

CONCLUSION

A clear positive association was identified between milk intake frequency and fracture risk among Japanese women after menopause with low 25(OH)D levels. Therefore, correcting vitamin D insufficiency would likely lower fracture risk. In addition, encouraging habitual milk intake may help prevent fractures, particularly among individuals with low 25(OH)D levels.