Association between vitamin D and bone mineral density in Japanese adults: the Unzen study

Summary We showed an association between serum concentrations of vitamin D and bone health among community-dwelling adults in Japan after adjustment for confounding factors, with 730 participants in a city, with concentrations of 25(OH) vitamin D, and with parameters of quantitative ultrasound. Purpose The primary objective of this study was to examine the correlation between serum 25-hydroxyvitamin D (25(OH)D) concentration and bone indicators as measured by quantitative ultrasound in middle-aged and older Japanese adults living in low-latitude seaside areas during summer and autumn. Methods We conducted a cross-sectional study, the Unzen study, on community-dwelling Japanese adults who participated to periodic health examinations between 2011 and 2013 (during the months of May to November). Results A total of 301 men (mean (SD) age, 67.9 (8.2) years; range, 50–92 years) and 429 women (mean (SD) age, 67.9 (7.7); range, 50–89 years) participated in this study. Serum 25(OH)D levels and quantitative ultrasound parameters (broadband ultrasound (BUA), speed of sound (SOS), and stiffness index of the calcaneus were measured for the participants. We excluded two men and 28 women from the 730 participants because they were on medication for osteoporosis. So, 299 men and 401 women were included in the final data analysis. The prevalence of vitamin D insufficiency (< 30 ng/ml) was very high: 71.9% in men and 95.5% in women. In women, the log(25(OH)D) positively and significantly correlated with SOS ( p = 0.011) and stiffness index ( p = 0.028) but not with BUA ( p = 0.176). In men, the log(25(OH)D) did not correlate with the BUA, SOS, or stiffness index ( p = 0.218, 0.420, and 0.262, respectively). Conclusions Serum 25(OH)D levels were associated with SOS or stiffness index in women but not in men.