Effect of Vitamin D Supplementation on Glucose Tolerance in Subjects at Risk for Diabetes With Low Vitamin D.

Type 2 diabetes (T2D) is an increasingly prevalent and serious condition whose risk appears to be increased by low serum vitamin D concentrations. Epidemiological studies show an association between increased diabetes risk and low serum vitamin D and studies suggest that vitamin D may protect against diabetes by reducing chronic inflammation and improving insulin sensitivity and insulin secretion. Although clinical studies show some of these effects, no studies have been able to show that vitamin D supplementation reduces post-prandial blood glucose, the most clinically relevant marker of diabetes and dysglycemia. Previously, the investigators showed that cheddar cheese and low-fat cheese can be fortified with high levels of vitamin D3 (28,000IU/ 30g portion) and that, in this form, it is at least as a effective as vitamin D3 supplements in raising serum vitamin D concentrations. Since post-prandial glucose is most sensitive to changes in insulin sensitivity the main purpose of this study is to determine the effect of vitamin D supplementation on oral glucose tolerance (ie. serum glucose 2h after 75g oral glucose) in individuals who are at risk for developing T2D. Secondary objective are to determine the effect of vitamin D supplementation on insulin sensitivity, insulin secretion, inflammatory markers, blood lipids and markers of safety including serum parathyroid hormone levels and urinary calcium excretion.

Inclusion criteria

• male or non-pregnant, non-lactating females, aged 18-75
• volunteered to participate by signing the consent form
• BMI <40kg/ m2
• vitamin D insufficient, defined as: serum 25(OH) vitamin D3 (25(OH)D) concentration ≤65nmol/ L
• increased risk for diabetes, defined as: FINDRISC score >10 for Caucasians or >6 for non-Caucasians OR presence of metabolic syndrome
• dysglycemia, defined as:fasting serum glucose 5.6 to 6.9 mmol/L, inclusive OR HbA1c 0.054 to 0.064, inclusive
• systolic blood pressure ≤150/95 mmHg if not being treated for hypertension or ≤140/90 mmHg if on treatment for hypertension.
• taking no prescription drugs, or stable (for at least 6 weeks) dose of birth control pill, or drug(s) used to treat hypertension, hyperlipidemia, depression or other mental illness or hypothyroid.
• taking no supplements, or stable (for at least 6 weeks) dose of supplement(s).

Exclusion criteria

• subjects not meeting all inclusion criteria
• history of renal failure or liver disease
• serum creatinine >1.8 times upper limit of normal (ULN)
• serum aspartate or alanine transaminase (AST,ALT) >3 times ULN
• current use of drug or drugs to treat diabetes or use of steroids or pancreatic enzymes
• within 6 weeks of randomization, change in dose of supplements or drug(s) used to treat hypertension, hyperlipidemia, depression or other mental illness or hypothyroid.
• use of antibiotics within 3 months.
• medical or surgical event requiring hospitalization within 3 months of randomization
• presence of any condition affecting nutrient absorption
• intolerance to cheese
• plan to travel outside Canada for more than 14 consecutive days during the trial