Vitamin D, Insulin Secretion, Sensitivity, and Lipids
Results From a Case-Control Study and a Randomized Controlled Trial Using Hyperglycemic Clamp Technique
- 1Tromsø Endocrine Research Group, Department of Clinical Medicine, University of Tromsø, Tromsø, Norway
- 2Division of Internal Medicine, University Hospital of North Norway, Tromsø, Norway
- 3Department of Medical Biology, University of Tromsø, Tromsø, Norway
- 4Department of Medical Biochemistry, University Hospital of North Norway, Tromsø, Norway
- 5Hormone Laboratory, Haukeland University Hospital, Bergen, Norway
- Corresponding author: Guri Grimnes, .
OBJECTIVE Vitamin D deficiency is associated with an unfavorable metabolic profile in observational studies. The intention was to compare insulin sensitivity (the primary end point) and secretion and lipids in subjects with low and high serum 25(OH)D (25-hydroxyvitamin D) levels and to assess the effect of vitamin D supplementation on the same outcomes among the participants with low serum 25(OH)D levels.
RESEARCH DESIGN AND METHODS Participants were recruited from a population-based study (the Tromsø Study) based on their serum 25(OH)D measurements. A 3-h hyperglycemic clamp was performed, and the participants with low serum 25(OH)D levels were thereafter randomized to receive capsules of 20,000 IU vitamin D3 or identical-looking placebo twice weekly for 6 months. A final hyperglycemic clamp was then performed.
RESULTS The 52 participants with high serum 25(OH)D levels (85.6 ± 13.5 nmol/L [mean ± SD]) had significantly higher insulin sensitivity index (ISI) and lower HbA1c and triglycerides (TGs) than the 108 participants with low serum 25(OH)D (40.3 ± 12.8 nmol/L), but the differences in ISI and TGs were not significant after adjustments. After supplementation, serum 25(OH)D was 142.7 ± 25.7 and 42.9 ± 17.3 nmol/L in 49 of 51 completing participants randomized to vitamin D and 45 of 53 randomized to placebo, respectively. At the end of the study, there were no statistically significant differences in the outcome variables between the two groups.
CONCLUSIONS Vitamin D supplementation to apparently healthy subjects with insufficient serum 25(OH)D levels does not improve insulin sensitivity or secretion or serum lipid profile.
- Received May 13, 2011.
- Accepted August 10, 2011.
- © 2011 by the American Diabetes Association.
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