The Relationship of Physical Performance and Osteoporosis Prevention with Free Vitamin D in Older African Americans

Presentation Number: SUN 346
Date of Presentation: April 2nd, 2017

Ruban Dhaliwal*, Mageda Mikhail, Gianina Usera, Alexandra Stolberg, Shahidul Islam, Louis Ragolia and John F Aloia
Winthrop University Hospital

Abstract

Introduction: Vitamin D deficiency is associated with bone loss, poor physical performance and muscle strength. Older adults require higher intake of vitamin D to overcome secondary hyperparathyroidism related to aging. Little information is available on prevention or management of bone loss, or extra skeletal effects of vitamin D in older African Americans.

Objective: This was a randomized, double-blind, placebo controlled trial designed to examine the effect of vitamin D on bone mass and physical performance in older African American women. Here we report the design and baseline findings of this study.

Methods: In this four-year intervention trial, 258 healthy African American women, older than 60 years of age, were assigned to receive either placebo or vitamin D3. Initial vitamin D3 dose was determined by the baseline serum 25OHD levels. The vitamin D3 dose was adjusted further at 3-month intervals to maintain serum 25OHD level between 75-172 nmol/L. Subjects with baseline 25OHD level ≤20 nmol/L or ≥65 nmol/L were excluded. Objective measures of anthropometric variables and neuromuscular strength [as measured by Short Physical Performance Battery (SPPB), grip strength and gait speed] were obtained. Calcium supplements were provided to ensure a total calcium intake of 1200 mg/d. Markers of bone turnover, vitamin D metabolites, and parathyroid hormone levels were measured in serum. Additional assessment included bone mineral density (BMD) every 6 months.

Results: No significant differences in baseline characteristics (demographics, BMD, muscle mass, grip strength, serum total 25OHD and free 25OHD) were noted between the active and control groups. There was significant difference in the SPPB total score (10.9 ± 1.5 versus 10.4 ± 1.8, P=0.008) between the two study groups. None of the measures of physical performance (SPPB total score, grip strength or gait speed) showed association with baseline serum 25OHD concentration. Both, grip strength and gait speed showed a significant correlation with free 25OHD level. One pg/ml increase in free 25OHD predicted a 1.36 lb increase in grip strength (after adjusting for age and BMI, P=0.041) and a 28% increase in the odds of having higher gait speed score (age adjusted OR (95% CI) =1.28 (1.03-1.60), P=0.027).

Conclusions: Recent studies have questioned the definition of adequacy of vitamin D in African Americans and raised a concern that lower total serum 25OHD may be misleading in keeping with the lower vitamin D binding protein level and comparable free serum 25OHD. This is the first study to show association between free 25OHD and physical performance. These findings indicate a positive relationship of free 25OHD with grip strength and gait speed in older African Americans. Whether free 25OHD is a better biomarker of vitamin D status than total 25OHD remains undetermined. Additional studies are needed to better understand the role of free 25OHD.

 

Nothing to Disclose: RD, MM, GU, AS, SI, LR, JFA