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.