Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Dietetics and Nutrition

Advisor's Name

Fatma G. Huffman

Advisor's Title

Committee Chair

Advisor's Name

Juan Liuzzi

Advisor's Name

Paulette Johnson

Advisor's Name

Zisca Dixon

Advisor's Name

Marianna Baum

Date of Defense

2-21-2012

Abstract

This cross sectional study investigated the association between 25-hydroxyvitamin D (25(OH)D) levels, vitamin D receptor (VDR) polymorphisms, HOMA2 and diabetes status in Cuban Americans, Haitian Americans, and African Americans. The sample for the study included a total of 885 participants (Cuban American = 370; Haitian American = 259; African American = 256). Serum 25(OH)D levels were determined using a commercial ELISA kit from Immunodiagnostic Systems Limited. Polymerase chain reaction-restriction fragment length polymorphism (PCR- RFLP) was used for genotyping BsmI and TaqI, Real-time- Polymerase chain reaction (RT-PCR) was used for ApaI. HOMA2 model calculations were used as a surrogate marker for insulin resistance, insulin sensitivity and β-cell function. All statistical analyses were performed using SPSS (Version 18.0, Chicago, IL, U.S.). Student’s t-test and analysis of variance (ANOVA), c2 test and logistic regression analysis were used.

We found that Cuban Americans without T2D had significantly lower odds of having insufficient 25(OH)D compared to all other groups. Participants with darker skin (Haitian Americans and African Americans) and those with T2D had the greatest risk of having insufficient levels of 25(OH)D. Cuban Americans with T2D had a protective factor for vitamin D insufficiency if they carried the TaqI genotype (tt) (p < 0.02) and Cuban Americans without T2D had the highest β-cell function levels (p < 0.05).

Further investigation is needed to have a better understanding of the role vitamin D, VDR polymorphisms and the role HOMA2 model plays in the three ethnicities. Awareness of the high prevalence of vitamin D insufficiency among Haitian Americans and African Americans and also in those with T2D may sensitize physicians and dietitians to increase efforts to prevent vitamin D insufficiency. Further research to investigate the role and mechanism of action of vitamin D and diabetes is warranted.

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