Projections from NHANES III indicate that approximately 12,000,000 US adults 60 years of age have vitamin D insufficiency (serum 25(OH)D < 50 nmol/L). A growing body of evidence suggests that vitamin D insufficiency and/or its associated secondary hyperparathyroidism accelerates the disablement process not only through effects on bone density and fractures but also through direct effects on muscular function which we hypothesize lead to higher rates of mobility limitation and falls. Since vitamin D insufficiency is common even in community-dwelling elderly, and the cost of remediating suboptimal levels is low, a better understanding of the relationship between vitamin D status and function in older adults is of significant public health importance. To advance our understanding of the role of vitamin D in function and bone health, the investigators propose to measure circulating 25(OH)D and parathyroid hormone (PTH) levels in archived samples from the Health, Aging and Body Composition (Health ABC) Study, a cohort of 3,075 black and white well-functioning community-dwelling men and women aged 70-79 yrs at baseline.
Three specific aims will be addressed:
Specific Aim 1. Determine whether vitamin D status as determined by circulating 25(OH)D and PTH affects the rate of incident mobility limitation over 6 years;
Specific Aim 2. Determine whether vitamin D status affects the rate of falls over 6 years;
Specific Aim 3. Determine the role of vitamin D status in fracture risk over 6 years. We will also examine vitamin D's role in trajectories of proximal mediators of these important outcomes (i.e., strength, balance, walking speed and bone mineral density). As secondary aims, we will evaluate: 1) alternative cut-points to inform the debate on vitamin D adequacy in older adults; 2) the role of PTH independent from vitamin D; and 3) the effects of dietary and supplementary vitamin D intake on function and bone. We will specifically examine the associations in African-Americans, a group at high risk for vitamin D insufficiency. Health ABC, with longitudinal data on important functional outcomes (mobility limitation, falls and fractures) and proximal mediators (strength, balance, walking speed and bone mineral density) is the ideal study to advance scientific knowledge in this area of high priority in a cost-effective and efficient manner. ? ? ? ?
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