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Vitamin D, Glucose Control and Insulin Sensitivity in African-Americans

This study has been completed.
Information provided by (Responsible Party):
Susan Harris, Tufts University Identifier:
First received: November 3, 2008
Last updated: November 13, 2014
Last verified: November 2014
North American blacks tend to have low blood levels of vitamin D because pigmentation blocks vitamin D production in the skin. They also have higher rates of developing type 2 diabetes and higher rates of complications from the disease compared with whites. Although there is compelling evidence that adequate vitamin D may reduce the risk for type 2 diabetes in whites, recent evidence from a national survey demonstrated an association of vitamin D with diabetes in whites but not in blacks. However, the central hypothesis of this study is that providing enough supplemental vitamin D to blacks (raising their blood levels higher than that of most participants in the survey) will improve blood measures related to diabetes risk. The proposed study is a 12-week randomized, double-blind, placebo-controlled experiment designed to examine the effect of vitamin D supplementation (100 μg/d ) on insulin secretion, insulin sensitivity and glucose control in pre-diabetic black men and women aged 40 and older.

Condition Intervention Phase
Type 2 Diabetes Dietary Supplement: cholecalciferol Other: microcrystalline cellulose Phase 2

Study Type: Interventional
Study Design: Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary Purpose: Prevention
Official Title: Vitamin D, Glucose Control and Insulin Sensitivity in African-Americans

Resource links provided by NLM:

Further study details as provided by Susan Harris, Tufts University:

Primary Outcome Measures:
  • Insulin secretion rate [ Time Frame: 12 weeks ]
  • Insulin sensitivity index [ Time Frame: 12 weeks ]
  • 2-hr post load glucose [ Time Frame: 12 weeks ]

Enrollment: 100
Study Start Date: July 2008
Study Completion Date: February 2011
Primary Completion Date: February 2011 (Final data collection date for primary outcome measure)
Arms Assigned Interventions
Experimental: 1 vitamin D3
vitamin D3, 4000 IU/d
Dietary Supplement: cholecalciferol
4000 IU/d
Other Names:
  • vitamin D3
  • vitamin D
Placebo Comparator: 2
Other: microcrystalline cellulose
Other Name: placebo


Ages Eligible for Study:   40 Years and older   (Adult, Senior)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   Yes

Inclusion Criteria:

  • African-American by self designation
  • Glucose intolerance defined as FPG ≥ 100 mg/dl or A1c ≥ 5.8%
  • BMI 25.0-39.9
  • Age 40 or older

Exclusion Criteria:

Medical Conditions

  • Diabetes potentially requiring pharmacotherapy, defined as A1c > 7%
  • Uncontrolled thyroid disease
  • Current parathyroid, liver or kidney disease
  • Renal stone within 5 years
  • Sarcoidosis, current pancreatitis, active tuberculosis, hemiplegia, gout
  • Inflammatory bowel disease, colostomy, malabsorption
  • Cancer other than basal cell skin cancer within 5 years
  • Uncontrolled arrhythmia in past year
  • Albinism or other condition associated with reduced skin pigmentation
  • Pregnancy over the last 1 year
  • Intent to become pregnant
  • Menopause onset within 1 year
  • Any other unstable medical condition Laboratory Tests
  • Fasting plasma glucose < 100
  • Hemoglobin A1c > 7%
  • Laboratory evidence of liver disease (e.g. AST > 70 U/L or ALT > 72 IU/L)
  • Laboratory evidence of kidney disease (e.g. estimated glomerular filtration rate < 60 ml/min/1.73 m2).
  • Elevated spot urine calcium to creatinine ratio > 0.38 mg/dl*
  • Abnormal serum calcium (serum calcium > 10.5 mg/dl)
  • Anemia (Hematocrit < 36% in men, <33% in women) Medications (use in past three months)
  • Estrogen or testosterone
  • Prescription vitamin D
  • Lithium
  • Oral corticosteroids
  • Anti-seizure medications
  • Unstable doses of psychotropics or phenothiazines
  • Cholestyramine Supplements (current use - may discontinue after screening)
  • Vitamin D supplements, cod liver oil, calcium supplements Other
  • Body mass index less <25 or > 39.9
  • Consumption of more than 14 alcoholic drinks per week
  • Inability to attend all three study visits as scheduled
  • Inability to provide written informed consent
  • age < 40 years
  • not African-American (by self-designation)
  • Participation in another research intervention study

    • corresponds to a 24-hour urinary calcium excretion > 400 mg
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Please refer to this study by its identifier: NCT00784511

United States, Massachusetts
Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University
Boston, Massachusetts, United States, 02111
Sponsors and Collaborators
Tufts University
  More Information

Responsible Party: Susan Harris, Scientist I, Tufts University Identifier: NCT00784511     History of Changes
Other Study ID Numbers: 8095
ADA 7-08-CR-27
Study First Received: November 3, 2008
Last Updated: November 13, 2014

Keywords provided by Susan Harris, Tufts University:
vitamin D
African Americans
insulin sensitivity
glucose control

Additional relevant MeSH terms:
Insulin Resistance
Immune System Diseases
Glucose Metabolism Disorders
Metabolic Diseases
Vitamin D
Hypoglycemic Agents
Physiological Effects of Drugs
Growth Substances
Bone Density Conservation Agents processed this record on August 18, 2017