Vitamin D insufficiency in Japanese female college students: a preliminary report

Vitamin D insufficiency, a risk factor for osteoporosis, has been well investigated in elderly women worldwide, but little information has been available for younger women. This study aimed to determine serum 25-hydroxyvitamin D [25(OH)D] levels in Japanese female college students, and to test whether there is an association between 25(OH)D and bone strength. Subjects were 77 Japanese female junior college students aged 19-24 years. Serum 25(OH)D was measured with high performance liquid chromatography. Bone strength of the calcaneus was evaluated using the osteo sono-assessment index (OSI), a combined index reflecting the bone mass, bone architecture, and elasticity, as measured by quantitative ultrasound densitometry (AOS-100, Aloka). The mean 25(OH)D concentration was 34.2 nmol/L (SD +/- 12.1). The proportion of subjects with 25(OH)D less than 30 nmol/L, a cut-off value for vitamin D insufficiency, was 31/77 (40.3%). Simple linear regression analysis showed that there was a significant linear relationship between 25(OH)D and OSI (R2 = 0.098, p = 0.0069). The association held even after adjusting for weight (partial R2 = 0.098, p = 0.0023). Body weight was also a significant predictor of OSI (partial R2 = 0.105, p = 0.0034). These results suggest that vitamin D insufficiency may be prevalent in healthy young women. Moreover, low levels of 25(OH)D in young women may adversely affect bone strength. An additional, newly designed epidemiological study with a sufficient sample size is needed to confirm the present findings.