Endocrine Abstracts

Objectives: The serum levels of 25-hydroxyvitamin D ([25 (OH) D]) is considered to be one of the most reliable biomarkers of vitamin D (VD) nutritional status. VD deficiency/insufficiency is a risk factor for osteoporotic fractures and falls. Even though established clinical significance of maintaining an adequate level of 25 (OH) D, the level of 25 (OH) D is easily fluctuated by diverse factors such as sunlight exposure, VD intake, renal function and body fat content. In addition, Fibroblast growth factor 23 (FGF23) has been shown to suppress and induce the conversion of 25 (OH) D to 1,25(OH)2D and to 24, 25 (OH)2D, respectively. These studies suggest that many other factors can influence the level of 25 (OH) D s. In the present study, we aimed to figure out factors that influence the level of 25 (OH) D in healthy postmenopausal women.

Methods: Two-hundred healthy postmenopausal women who had undergone osteoporosis screening were analyzed in this study. Serum levels of 25(OH)D, intact PTH, CTX, and FGF23 were measured. Bone mineral density (BMD) was measured using the DXA method at the lumbar vertebrae and femoral neck (FN). Nutrient intake was calculated using a food frequency questionnaire. Motor function tests included maximum step length (MSL), and grip strength.

Results: Mean values of age was 63.4 years with the following measurements: 25(OH)D 16.2 ± 4.3 ng/ml, serum creatinine (Cr) 0.6 ± 0.1 mg/dl, Ca intake 656 ± 192 mg/day, VD intake 9.9 ± 3.9 (range: 1.3–24.6) µg/day, MSL 102 ± 13 cm, grip strength 21.8 ± 4.5 kg, and the mean level of outdoor activity time 1.9 ± 1.6 h (range: 0–7.0 h). The level of 25 (OH) D was significantly associated with the age and VD intake (P<0.001); unexpectedly the length of outdoor activity appeared to be insignificant association. Multiple regression analysis demonstrated that VD intake was associated with 25 (OH) D after adjusting for age, body mass index, body fat percentage, the levels of Ca, P, PTH, Cr, CTX, FGF23, BMD(FN), length of outdoor activity, other nutrients intake, MSL and grip strength (r = 0.359, P = 0.003).

Conclusion: VD intake significantly influenced the concentration of 25 (OH) D after adjusting for various factors including the body fat percentage and renal function. Our findings suggest that nutritional interventions focused on VD intake are important to ensure VD sufficiency.