Screening for Vitamin D Deficiency in Black Americans: Comparison of Total, Free, Bioavailable 25 Hydroxy Vitamin D Levels with Parathyroid Hormone Levels and Bone Mineral Density.

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.

Survival effects of ZDV, ddI, and ddC in patients with CD4 < or = 50 cells/mm3.

Seven major clinical trials for the treatment of HIV-infected individuals are investigated. The treatments used in these trials were zidovudine, dideoxyinosine, dideoxycytosine, and one combination for patients with CD4 cell counts < 500 cells/mm3. Patients in each trial are partitioned into two subgroups based on their baseline CD4 cell counts: patients with CD4 < or = 50 cells/mm3 and patients with CD4 > 50 cells/mm3. The difference between treatment effects, using survival as a measure of effect, within each subgroup is calculated separately for each trial; this difference is referred to as "subgroup response." For each trial the difference between the subgroup responses is calculated and standardized. A meta-analysis is conducted over all seven trials for the differences between subgroup responses; the consistency of responses is evaluated across all trials among patients within baseline CD4 subgroups. Based on the result of this meta-analysis we conclude that there is no evidence that the treatment effects in patients with CD4 < or = 50 cells/mm3 are different from those among patients with CD4 > 50 cells/mm3. This result is observed in patients with different antiviral experience and different baseline characteristics. Risk ratios as well as chi 2 statistics are used to quantify the response rates in different subgroups. Kaplan-Meier curves of survival for these trials are depicted for all patients and each subgroup separately. In most of the trials the Kaplan-Meier curves for the patients with CD4 < or = 50 cells/mm3 resemble those for all patients.(ABSTRACT TRUNCATED AT 250 WORDS)