A Randomized, Placebo Controlled Trial of Vitamin D Supplementation to Improve Glycemia in Overweight and Obese African Americans
Susan S. Harris D.Sc.1,*, Anastassios G. Pittas M.D., M.S.1,2, Nancy J. Palermo B.S.1
1 Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University
2 Division of Endocrinology, Diabetes & Metabolism, Tufts Medical Center
*Dr. Susan Harris Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University 711 Washington St., Boston, MA 02111 617-556-3265 (voice) 617-556-3305 (fax) susan.harris at tufts.edu
Aims. Vitamin D deficiency may increase the risk for type 2 diabetes. African Americans tend to have poor vitamin D status and increased risk of diabetes, but effects of vitamin D supplementation on components of diabetes risk have not been tested in this group. This study was conducted to determine whether vitamin D supplementation improves insulin secretion, insulin sensitivity and glycemia in African Americans with prediabetes or early diabetes.
Materials and Methods. In this randomized, placebo controlled trial, we examined the effect of 4000 IU/day vitamin D3, on glycemia and contributing measures including insulin secretion, insulin sensitivity, and the disposition index over twelve weeks in 89 overweight or obese African Americans with prediabetes or early diabetes. Outcome measures were derived from oral glucose tolerance testing.
Results. Mean plasma 25-hydroxyvitamin D was about 40 nmol/l in the placebo and vitamin D groups at baseline and increased to 81 nmol/l with supplementation. Insulin sensitivity decreased by 4% in the vitamin D group compared with a 12% increase in the placebo group (P=0.034). Insulin secretion increased by 12% in the vitamin D group compared with a 2% increase in the placebo group (P=0.024) but changes in the disposition index were similar across groups. There was no effect of supplementation on post-load glucose or other measures of glycemia.
Conclusions. Supplementation with 4000 IU/d vitamin D3 successfully corrected vitamin D insufficiency and had divergent effects on insulin secretion and sensitivity with no overall effect on disposition index or glycemia. In this study, vitamin D supplementation for three months did not change the pathophysiology of pre-diabetes in overweight and obese African Americans.
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Started with 16 nanograms,
4,000 IU of vitamin D for 3 months resulted in 32 nanograms
Strongly suspect that they needed to use a loading dose AND higher daily dose of vitamin D to treat diabetes
in three months for a group which had three risk factors: diabetes, overweight, and dark skin
Should also have had co-factors: particularly Calcium and Magnesium