Dose-dependent Effects of Vitamin D on Bone Health

Unlike the measurement of bone density by DXA (a secondary outcome, see below), which estimates bone density based on assumptions of the depth of a 2-dimensional image of bone, HR-pQCT measurement of Tt.BMD provides a true volume based density measurement. HR-pQCT also provides a much higher resolution image of the region of interest than the image derived from a DXA measurement.

Units of this measurement are milligrams hydroxyapatite per cubic centimetre (mg HA/cm3).

The analysis will examine change in Tt.BMD at distal radius and tibia from baseline to measurements at 6, 12, 24, and 36 months.

HR-pQCT scans provide the ability to measure a true volumetric density of the bone region of interest and to study microarchitecture of both trabecular and cortical bone, from which an assessment of strength by Finite Element Analysis (FEA) can be determined: briefly, a 3-dimensional computer model of bone can be constructed from the HR-pQCT data, and subjected to strength testing. FEA software (FAIM, version 6.0, Numerics88 Solutions, Calgary, Canada) is used to estimate failure load (N) based on 2 % of the elements exceeding 7,000 μstrain.

The analysis examines change from baseline measured at 6, 12, 24, and 36 months.

Cortical density (Ct.BMD) is a morphological parameter of microarchitecture of bone, and is measured in mg HA/cm3

Cortical Porosityis a morphological parameter of microarchitecture of bone, and is measured in percent.

Trabecular density (Tb.BMD) is a morphological parameter of microarchitecture of bone, and is measured in mg HA/cm3

Trabecular density (Tb.BMD) is a morphological parameter of microarchitecture of bone, and is measured in mg HA/cm3

Trabecular number (Tb.N) is a morphological parameter of microarchitecture of bone, and is measured as mean number of trabeculae per unit of length (mm)

Dual X-ray absorptiometry (DXA) will be used to scan the distal radius, lumbar spine and the proximal femur to obtain an areal (two dimensional) estimate of bone mineral density (aBMD). DXA is the current clinical standard for measuring bone density. From the scan of the lumbar spine and left proximal femur (~ 1 min), aBMD (g/cm2) will be used to determine a subject-specific T-score (aBMD compared to reference mean for a young healthy adult) and this value will be compared to standard World Health Organization criteria to classify each subject as normal (T-score>-1), low bone density (-1 < T > -2.5) or osteoporotic (T score < -2.5). Change from baseline will be assessed at 12, 24 and 36 months.

Vitamin D deficiency has been associated with depression. We propose to examine whether our Vitamin D intervention has an effect on depression or other aspects of mental health. The SF-36 questionnaire will be administered at baseline and at 12, 24, and 36 months. This will be used to assess subjects' perception of their Quality of Life, specifically the Mental Health Component, and whether the intervention (Vitamin D dose assignment) is associated with changes in the SF-36 scores for Mental Health Component change over the course of the study.

PHQ-9 questionnaire will be used to assess any effect the Vitamin D intervention might have on depression symptoms. The PHQ-9 analog scale score will be measured at entry and at 3, 6 and 12 months, then annually. This is not expected to be a safety issue in recruiting healthy volunteers, but obviously could become one.

In addition to the markers identified as safety measures in "other outcomes" (serum and urine calcium, serum creatinine, etc), we will also obtain serum for measurement of markers of bone turnover: serum C-telopeptide of Type I Collagen (CTX), and Procollagen I N-terminal Propeptide. Measurements taken at baseline and at 3, 6, 12, 24, and 36 months. Still to be arranged: Under-carboxylated osteocalcin and osteocalcin.

The balance tests include standing with (a) two feet on the force platform with eyes open, (b) two feet on the force platform with eyes closed, (c) two feet on a foam pad with eyes open, and (d) two feet on a foam pad with eyes closed. All tests will be performed 3 times, and a blindfold will be used for all eyes-closed assessments. The total testing time is approximately 15 minutes. Measurements done at baseline and at 12, 24 and 36 months

The main concern in safety of vitamin D consumption is the avoidance of toxicity in the form of hypercalcemia or renal damage, related to hypercalcemia and hypercalciuria. Two of the doses in this study are generally accepted as safe. The 10,000 IU daily dose exceeds the recommended upper limit of safe, unsupervised vitamin D intake, hence, this trial includes regular clinical laboratory testing of parameters of calcium metabolism, including serum and urine calcium, parathyroid hormone, 25OH-Vitamin D. Measurements will be done at baseline, 3, 6, 12, 24, and 36 months

Hemoglobin A1C, and fasting glucose, and the osteocalcin measurements will address some of the potential effects of vitamin D on glucose metabolism. A full assessment of the effects of vitamin D on diabetes and glucose metabolism is beyond the scope of this proposal, but because these parameters are very easily obtained measurements they will be examined at baseline, 3, 6 , 12, 24 and 36 months.

Recently, it has become apparent that the HRpQCT images obtained at the distal radius and tibia include enough detail of the arteries providing blood supply to the hand and foot, that quantification of calcification of the medial layer of these blood vessels (radial and ulnar arteries, anterior and posterior tibial arteries), may be possible. Vitamin D might play a role in vascular calcification (animal models suggest protection; vitamin D toxicity may be associated with soft tissue calcification). Consequently, the range and duration of vitamin D Dose in this protocol may allow discovery of a vitamin D effect on calcium deposition.

Reference: Patsch JM, Zulliger MA, Vilayphou N, et al. Quantification of lower leg arterial calcifications by high-resolution peripheral quantitative computed tomography. Bone. 2014 Jan;58:42-7.