The association of vitamin D status with bone mineral density (BMD) and Quantitative Ultrasound measurements (QUS) has been inconsistent in previous studies, probably caused by moderating effects. This study explored (1) the association of vitamin D status with QUS and BMD, and (2) whether these associations were modified by body mass index (BMI), age, gender, or physical activity. Two-independent cohorts of the Longitudinal Aging Study Amsterdam (LASA-I, 1995/1996, aged ≥65; LASA-II, 2008/2009, aged 61–71) and baseline measurement of the B-vitamins for the prevention of osteoporotic fractures (B-PROOF) study (2008–2011, aged 65+) were used. QUS measurements [broadband ultrasound attenuation (BUA) and speed of sound (SOS)] were performed at the calcaneus in all three cohorts (N = 1,235, N = 365, N = 1319); BMD was measured by Dual X-ray absorptiometry (DXA) in B-PROOF (N = 1,162 and 1,192 for specific sites) and LASA-I (N = 492 and 503). The associations of vitamin D status with BUA and BMD were modified by BMI. Only in persons with low-to-normal BMI (<25 kg/m<sup>2</sup>) and serum 25(OH)D <25 nmol/L was associated with lower BUA as compared to the reference group (≥50 nmol/L) in LASA-I and B-PROOF. Furthermore, in LASA-I, these individuals had lower BMD at the hip and lumbar spine. In LASA-II, no associations with BUA were observed. Vitamin D status was not associated with SOS, and these associations were not modified by the effect modifiers tested. The association between vitamin D status and BUA and BMD was modified by BMI in the older-aged cohorts: there was only an association in individuals with BMI <25 kg/m<sup>2</sup>.

Body mass index, Bone mineral density, Older individuals, Quantitative ultrasound, Vitamin D,
Calcified Tissue International
Department of Internal Medicine

Sohl, E, de Jongh, R.T, Swart, K.M.A, Enneman, A.W, van Wijngaarden, J.P, van Dijk, S.C, … van Schoor, N.M. (2014). The Association Between Vitamin D Status and Parameters for Bone Density and Quality is Modified by Body Mass Index. Calcified Tissue International, 96(2), 113–122. doi:10.1007/s00223-014-9943-7