title: Vitamin D, insulin secretion, sensitivity, and lipids: results from a case-control study and a randomized controlled trial using hyperglycemic clamp technique.
abstract: 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.
  
  
  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 D(3) 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 HbA(1c) 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.
authors.affiliation: Tromsø Endocrine Research Group, Department of Clinical Medicine, University of Tromsø, Tromsø, Norway. guri.grimnes@unn.no
authors.forename: Guri
authors.initials: G
authors.lastname: Grimnes
authors.forename: Yngve
authors.initials: Y
authors.lastname: Figenschau
authors.forename: Bjørg
authors.initials: B
authors.lastname: Almås
authors.forename: Rolf
authors.initials: R
authors.lastname: Jorde
mesh_terms: D000328:Adult; D000368:Aged; D002112:Calcifediol / Q000097:blood; D002214:Capsules; D002239:Carbohydrate Metabolism, Inborn Errors / Q000209:etiology / Q000517:prevention & control; D016022:Case-Control Studies; D002762:Cholecalciferol / Q000627:therapeutic use*; D019587:Dietary Supplements; D005260:Female; D015309:Glucose Clamp Technique; D006442:Glycated Hemoglobin / Q000032:analysis; D005991:Glycerol Kinase / Q000172:deficiency; D006801:Humans; D006943:Hyperglycemia / Q000209:etiology / Q000517:prevention & control; D000075262:Hypoadrenocorticism, Familial; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D007333:Insulin Resistance; D000078790:Insulin Secretion; D008055:Lipids / Q000097:blood*; D008297:Male; D008875:Middle Aged; D014280:Triglycerides / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000378:metabolism / Q000517:prevention & control*
chemical_list: D002112:Calcifediol; D002214:Capsules; D002762:Cholecalciferol; D006442:Glycated Hemoglobin; D005991:Glycerol Kinase; D007328:Insulin; D008055:Lipids; D014280:Triglycerides; C517652:hemoglobin A1c protein, human