African-Americans need only 20 ng of vitamin, not 30 ng, based on iPTH – Sept 2012

2nd study on this page disagrees - finding NO iPTH plateau

Defining physiologically “normal” vitamin D in African Americans

OSTEOPOROSIS INTERNATIONAL; Volume 23, Number 9 (2012), 2283-2291,
N. C. Wright (1), L. Chen (2), J. Niu (3), T. Neogi (3), K. Javiad (4), M. A. Nevitt (5). C. E. Lewis (6), J. R. Curtis (2)[email protected]

1. Department of Epidemiology, University of Alabama at Birmingham, RPHB 523, 1665 University Blvd, Birmingham, AL 35294, USA
2. Division of Clinical Immunology and Rheumatology, University of Alabama at Birmingham, FOT 805, 510 20th Street South, Birmingham, AL 35294, USA
3. Clinical Epidemiology Research & Training Unit, Boston University School of Medicine, 650 Albany St., X Building, Suite, 200, Boston, MA 02118, USA
4. Oxford NIHR Musculoskeletal Biomedical Research Centre, University of Oxford, Nuffield Orthopaedic Centre, Windmill Road, Oxford, OX3 7LD UK
5. Division of Clinical Trials & Multicenter Studies, University of California San Francisco, UCSF Box 0560, 185 Berry Street, Lobby 5, Suite 5700, San Francisco, CA 94107, USA
6. Division of Preventive Medicine, University of Alabama at Birmingham, MT 614, 1717 11th Avenue South, Birmingham, AL 35294, USA

Summary
The relationship between serum 25(OH)D and intact parathyroid hormone (iPTH) was evaluated in the Multicenter Osteoarthritis Study (MOST).
No further change in iPTH was observed for African Americans with 25(OH)D levels above 20 ng/ml, suggesting that compared to Caucasians, lower vitamin D targets for sufficiency may be appropriate for African Americans.

Introduction
Vitamin D levels >30 ng/ml are commonly considered “normal” based upon maximal suppression of iPTH; however, this has recently been challenged and the optimal 25(OH)D level among non-Caucasians is unclear. We evaluated the cross-sectional relationship between serum 25(OH)D and iPTH in a sample of Caucasian and African American adults.

Methods
We used baseline serum samples of participants from the Multicenter Osteoarthritis Study (MOST) for this analysis and used three methods to model the relationship between 25(OH)D and iPTH: ordinary least squares regression (OLS), segmented regression and Helmert contrasts.

Results
Among Caucasians (n?=?1,258), 25(OH)D and iPTH ranged from 4 to 51 ng/ml and 2 to 120 pg/ml and from 3 to 32 ng/ml and 3 to 119 pg/ml in African Americans (n?=?423). We observed different thresholds between African Americans and Caucasians using each analytic technique. Using 25(OH)D as a categorical variable in OLS, iPTH was statistically higher at lower 25(OH)D categories than the 24–32 ng/ml referent group among Caucasians. However, in African Americans, the mean iPTH was only significantly higher at 25(OH)D levels below 15 ng/ml.

Using segmented regression, iPTH appeared to stabilize at a lower 25(OH)D level in African Americans (19–23 ng/ml) compared to in Caucasians (>32 ng/ml).

Helmert contrasts also revealed a lower threshold in African Americans than Caucasians.

Conclusion
Among MOST participants, the 25(OH)D thresholds at which no further change in iPTH was observed was approximately 20 ng/ml in African Americans versus approximately 30 ng/ml in Caucasians, suggesting optimal vitamin D levels in Caucasians may not be applicable to African Americans.

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ASSOCIATION BETWEEN 25-HYDROXYVITAMIN D AND INTACT PARATHYROID HORMONE LEVELS ACROSS LATITUDE AMONG ADULTS WITH AFRICAN ANCESTRY

Endocr Pract. 2016 Aug;22(8):911-9. doi: 10.4158/EP151079.OR. Epub 2016 Apr 4.
Kramer H, Camacho P, Aloia J, Luke A, Bovet P, Rhule JP, Forrester T, Lambert V, Harders R, Dugas L, Cooper R, Durazo-Arvizu R.

OBJECTIVE:
To compare levels of 25-hydroxyvitamin D (25[OH]D) associated with a plateauing of intact parathyroid (iPTH) across latitudes among adults with African ancestry.
METHODS:
This study included approximately 500 adults of African ancestry ages 25 to 45 years living in 4 sites: Chicago, Illinois (41°N), Jamaica (17°N), Ghana (6°N), and South Africa (34°S). Multivariate linear regression models, a nonlinear logistic growth curve model, and piecewise linear models with a single knot were fitted to estimate the 25OHD level associated with a plateauing of iPTH with adjustment for covariates. Goodness of fit was compared using computer intensive permutation tests.
RESULTS:
Mean age was 34.7 (SD 6.2) years, and 46.5% were male. Within each site, the percentage of participants with an iPTH level ≥65 pg/mL was higher among females versus males and was most frequent among South African females (17.1%) and lowest among Jamaican males (0.6%). Goodness of fit tests supported linear regression as the preferred model for the association between iPTH and 25[OH]D in the 4 sites with no 25[OH]D level associated with iPTH plateauing in any site. The slope of the association between 25[OH]D and iPTH differed by latitude; it was strongest in the U.S. (β = -0.81; 95% confidence interval [CI] = -1.03, -0.59), and weakest in Jamaica (β = -0.45; 95% CI -0.71, -0.18) with covariate adjustment, but differences in slopes were small.
CONCLUSION:
The association between 25[OH]D and iPTH appears linear among adults with African ancestry regardless of latitude within a range of 25[OH]D levels between 10 and 60 ng/mL.

PMID: 27042745 DOI: 10.4158/EP151079.OR

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See also Vitamin D Life

• Overview Dark Skin and Vitamin D
• Dark skinned people may not need as much vitamin D – April 2012
• All items in Dark Color and Vitamin D 425 items
• Blacks may not need as much Vitamin D many articles
• Africans in Europe might only need 19 ng of vitamin D – estimated from PTH July 2011
• 20 ng of vitamin D is enough for African American PTH – Dec 2011