Vitamin D, Insulin Secretion, Sensitivity, and Lipids

Diabetes
Q1
Oct 2011
Citations:131
Influential Citations:6
Interventional (Human) Studies
93
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Methods
Design: nested case-control study within a population-based Tromsø Study and a randomized, double-blind, placebo-controlled trial. Participants: adults aged 30-75 years; nested portion included 108 case subjects with low serum 25(OH)D and 52 control subjects with high serum 25(OH)D; exclusions included diabetes, acute myocardial infarction or stroke in the past 12 months, cancer in the past 5 years, steroid use, kidney dysfunction, pregnancy, lactation, or contraception restrictions. In the randomized trial, 108 case subjects with low 25(OH)D were randomized to vitamin D or placebo for 6 months; insulin secretion and sensitivity were measured by a hyperglycemic clamp, with lipid parameters and HbA1c also assessed.
Intervention
Vitamin D3; 20,000 IU per capsule; two capsules per week; duration 6 months; taken orally.
Results
Observationally, higher baseline serum 25(OH)D was associated with higher insulin sensitivity and lower HbA1c and triglycerides, but adjustments for covariates attenuated ISI and TG differences. In the randomized trial, 6 months of vitamin D supplementation raised 25(OH)D to 142.7 ± 25.7 nmol/L (n=49) vs 42.9 ± 17.3 nmol/L (n=45) with placebo, but there were no significant between-group differences in insulin secretion (AUC0–10 min, AUC120–180 min), insulin sensitivity (ISI), glucose tolerance (M), HbA1c, triglycerides, or lipids after 6 months. Within-group increases in fasting glucose and HbA1c occurred in the vitamin D group, but between-group differences were not significant. Safety: no hypercalcemia or kidney stones; one death in placebo. Conclusion: Vitamin D supplementation in apparently healthy, vitamin D–insufficient adults does not improve insulin sensitivity, insulin secretion, or lipid profile over 6 months.
Limitations
Limited power to detect small differences due to sample size; relatively short duration (6 months); population largely Caucasian, limiting generalizability; observational portion subject to confounding (e.g., physical activity, diet); dropout/adherence considerations.

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...