Related Experiment Video
Updated: Feb 3, 2026
Author Spotlight: Unraveling Vitamin A Transport Mechanisms — Linking Liver Receptors to Vision Health Through RBPR2 and RBP4 Interactions
Published on: October 4, 2024
Screening for Vitamin D Deficiency in Black Americans: Comparison of Total, Free, Bioavailable 25 Hydroxy Vitamin D
A McKee1, S M Lima Ribeiro, T K Malmstrom
1Alexis McKee, MD, Division of Endocrinology, Diabetes and Metabolism, Saint Louis University School of Medicine, 1402 S. Grand Blvd., M412, St. Louis, MO 63104, (314) 977-8458,
Objectives:
There is debate surrounding the adequacy of total and free 25 hydroxy vitamin D [25(OH)D] levels in black Americans who have inherently high bone mineral density [BMD] and low serum concentration of vitamin D binding proteins [VDBP].
Design:
Retrospective analysis of serum samples and BMD analyses from the African American Health Study [AAHS] cohort.
Setting:
The AAHS is a population-based longitudinal study initiated to examine issues of disability and frailty among urban-dwelling black Americans in the city of Saint Louis, Missouri.
Participants:
122 men and 206 women, age 60.2 ± 4.3 years.
Intervention:
Retrospective analysis.
Measurements:
Total 25(OH)D, VDBP, PTH, and BMD of the lumbar spine and hip by dual energy x-ray photometry (DXA). Free and bioavailable vitamin D levels were calculated using serum concentrations and affinity constants for the VDBP (Gc1F and Gc1S) phenotypes.
Results:
Serum total 25(OH)D levels were 14.6 ± 8.9 ng/mL (36 ± 22 nmol/L). Vitamin D insufficiency was estimated by compensatory elevations of PTH above the normal range (> 65 pg/mL). PTH levels were within the normal reference range in > 95% of the samples at total 25(OH)D levels ≥ 20 ng/mL (≥50 nmol/L). There was no difference in the correlation of the reciprocal relationship of vitamin D vs parathyroid hormone between the VDBP phenotypes. Receiver operating characteristic curve analyses indicated that serum total 25(OH)D discriminated sufficiency from insufficiency at least as well as the calculated levels of the free and bioavailable vitamin D. Very low levels of total 25(OH)D (≤ 8 ng/mL, ≤20 nmol/L) were associated with decreased BMD (p=0.02), but higher levels of 25(OH)D did not show statistical differences in BMD.
Conclusion:
Total 25(OH)D levels of ≤ 8ng/mL (≤20 nmol/L) are associated with clinically significant changes in BMD, whereas total 25(OH)D levels ≥ 20 ng/mL (≥50 nmol/L) suppressed PTH and were not associated with deficiencies in BMD. Lower levels of 25(OH)D may be acceptable for bone health in black than in white Americans.
More Related Videos
Related Concept Videos
01:27Mineral, Vitamin and Water Absorption
01:30Vitamins
01:25Role of Vitamins in Maintaining Bone Health
Vitamin A
Vitamin A is involved in the process of bone remodeling. Retinoic acid, the active metabolite of Vitamin A, has nuclear receptors in osteoblasts and osteoclasts, which are involved in bone remodeling.
Vitamin B12
Vitamin B12 acts as a cofactor during the formation of osteoblast-related proteins, such as osteocalcin. Vitamin B12 plays a role...
01:29Leveling Effect
01:23Role of Skin in Vitamin D Synthesis
The solar UV B rays (290-315 nm) are absorbed by the skin, and 7-dehydrocholesterol (provitamin D3) photolyzes it to previtamin D3, which undergoes a rapid transformation to vitamin...
01:19High-Level and Low-Level Awareness