Role of Vitamin D in the Prevention and Treatment of Diseases Associated With Insulin Resistance
Condition: Vitamin D-deficient; Insulin-resistant
MeSH terms: Insulin Resistance
Study type: Interventional

Summary: 
      Prospective, randomized and placebo-controlled 6-month trial of vitamin D supplementation in
      130 Caucasian and vitamin D-deficient men and women aged 25 years and over. Participants will
      have abdominal obesity and at least one factor associated with insulin resistance.
      Participants will be randomized by sex, BMI and age. The primary aim is to compare the effect
      of daily vitamin D3 (cholecalciferol, 5000 IU) vs. placebo for 6 mo on insulin sensitivity
      (M-value by the gold standard method, the euglycemic hyperinsulinemic clamp). Secondary aims
      are to evaluate the effects of vitamin D3 vs. placebo on other indices of glucose metabolism,
      the lipid profile, blood pressure and anthropometric measurements. Questionnaires on physical
      activity and sunlight exposure, and a food frequency questionnaire will be administered at 0
      and 6 mo to adjust for confounding factors. At 0 and 6 mo, changes in serum 25(OH)D will be
      correlated with changes in blood markers associated with insulin sensitivity [hs-CRP,
      inflammatory cytokines (IL-6 and TNF-alpha), adiponectin, leptin, total and undercarboxylated
      osteocalcin].

      This research project intends to test 2 major hypotheses: (1) that vitamin D deficiency plays
      a causal role in the pathogenesis of insulin resistance in humans; and (2) that vitamin D
      increases insulin sensitivity.
    

Detailed description: 
      Part 1: Prospective, randomized and placebo-controlled 6-month trial of vitamin D
      supplementation in 130 Caucasian and vitamin D-deficient [serum 25(OH)D ≤55 nM] men and women
      aged 25 years and over with a BMI ≤40 kg/m2. Participants will have abdominal obesity
      (increased waist circumference of at least 102 cm for men and 88 cm for women) and at least
      one factor associated with insulin resistance, namely: (1) serum triglyceride levels of at
      least 1.7 mmol/L or treated dyslipidemia; (2) prediabetes or untreated type 2 diabetes (HbA1c
      >=5.6% or fasting glucose >=5.6 mmol/L or glucose 2h post OGTT >=7.8 mmol/L); (3) first
      degree relative with type 2 diabetes; (4) history of gestational diabetes. Participants will
      be randomized according to sex, BMI (<30 kg/m2 vs. 30 kg/m2 and over) and age (< or >=50
      years old). The primary aim is to compare the effect of daily vitamin D3 (cholecalciferol,
      5000 IU) vs. placebo for 6 mo on insulin sensitivity (M-value by the gold standard method,
      the euglycemic hyperinsulinemic clamp). Secondary aims are to evaluate the effects of vitamin
      D3 vs. placebo on other indices of glucose metabolism (fasting glucose, 2-h plasma glucose
      post OGTT, HbA1c, insulin sensitivity index (HOMA-IS using fasting glucose and insulin),
      insulin secretion index (HOMA-B using fasting glucose and C-peptide), insulinogenic index
      [(C-peptide at 30 min post OGTT - C-peptide at 0 min)/(glucose at 30 min post OGTT - glucose
      at 0 min)] and disposition index (insulinogenic index x M-value)), the lipid profile, blood
      pressure and anthropometric measurements (weight, waist and hip circumference, bioimpedance
      analysis). Questionnaires on physical activity and sunlight exposure, and a food frequency
      questionnaire will be administered at 0 and 6 mo to adjust for confounding factors. At 0 and
      6 mo, biochemical markers associated with insulin sensitivity will be measured (point 2).

      Part 2: Mechanistic studies comparing, before and after vitamin D3 supplementation, changes
      in serum 25(OH)D with changes in blood markers associated with insulin sensitivity [hs-CRP,
      inflammatory cytokines (IL-6 and TNF-alpha), adiponectin, leptin, total and undercarboxylated
      osteocalcin].
    

Intervention name(s): Vitamin D; Placebo
Intervention type(s): Dietary Supplement; Other
Intervention MeSH terms: Vitamin D
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Participant, Investigator)
Primary purpose: Prevention
Keywords: Vitamin D supplementation; Insulin resistance