A New Paradigm for Vitamin D Sufficiency

Overview

Although the African-American (AA) population tends to have lower serum 25(OH)D levels compared to whites, there is no evidence that the lower 25(OH)D levels in African-Americans are harmful. In fact, skeletal health is superior in AA. It is clear that total serum 25(OH)D concentrations do not reflect the same risk/benefit ratio in AA compared to white women and is, therefore, an inappropriate biomarker in this population. The investigators wish to investigate whether free 25(OD)D and Vitamin D Metabolite Ratio (VMR, ratio of 25(OH)D to 24,25(OH)2D) are preferable biomarkers to total 25(OH)D. The investigators propose a six month randomized double blinded study.

The specific aims of this study are as follows: 1. To establish that free 25(OH)D and VMR are similar in black and white populations. 2. To characterize the relationships between free 25(OH)D and VMR and two measures of bone health (PTH and BMD) in black and white women. 3. To evaluate whether the relationship of free 25(OH)D (and in parallel analyses, VMR) and bone health are stronger than those based on total 25(OH)D. 4. To evaluate whether free 25(OH)D and VMR respond to vitamin D intake (dose-response) in a similar manner to total 25(OH)D. The study population is postmenopausal Caucasian women age 60 and older. This six month study includes four visits. These results will be compared to those from a study in AA women which the investigators are also completing. There are two study groups. One group will receive vitamin D supplementation, the other a placebo. Subjects will be asked to refrain from taking outside Vitamin D supplements for the duration of the study. If the subject is eligible based on the results from the first two visits, the subject will be randomized into one of these two groups. Randomized subjects will be taking the vitamin D or placebo for a period of 6 months and will have one visit at the 3 month mark and a final visit at the 6 month mark. At the 3-month visit, the following procedures will be conducted: obtain interim medical and travel history, vital signs, weight, and height measured by the Harpenden Stadiometer, record adverse events and concomitant medications, Fasting blood collection: total 25(OH)D (by Diasorin), PTH, serum calcium and creatinine, Fasting urine collection for calcium and creatinine, and questionnaires: calcium food frequency questionnaire, quality of life questionnaire, falls and flu questionnaires. Subjects will be instructed on how to collect a 24-hour urine sample (for final visit) and collection container will be dispensed. Unused study supplements will be collected and counted, and study supplements will be dispensed based on serum 25(OH)D level algorithm. At the 6-month visit, in addition to what is completed at the 3-month visit, the following procedures will also be conducted:24-hour urine calcium, sodium, oxalate and creatinine; mini-mental health examination; physical performance examination (SPPB); and a physical activity questionnaire. Unused study supplements will be collected and counted. No further supplementation will be provided.