Studies about vitamin D and type 1 diabetes:
Glycemic Changes After Vitamin D Supplementation in Patients with Type 1 Diabetes Mellitus and Vitamin D Deficiency (2010)
Conclusion: Prospective study took 80 type-1 diabetic, vitamin D-deficient patients and had them take 4,000 IU vitamin D3 daily for 3 months to test vitamin D’s effect on blood sugar levels. There was a significant decrease in patient blood sugar levels among the entire group and those who achieved higher blood vitamin D levels enjoyed a greater decrease in blood sugar levels.
Note: Article covering a variety of studies documenting that kids with type-1 diabetes have much higher rates of vitamin D deficiency compared to non-diabetic kids.
Vitamin D Supplementation in Early Childhood and Risk of Type 1 Diabetes: A Systematic Review and Meta-Analysis (2008)
Conclusion: A meta-analysis of five different studies investigating the link between vitamin D supplementation during infancy and early childhood and later development of type 1 diabetes found that children who take supplemental vitamin D are at a lower risk for type 1 diabetes. The meta-analysis involved 1,528 children with type 1 diabetes and 5,156 healthy controls.
The Association Between Ultraviolet B Irradiance, Vitamin D Status and Incidence Rates of Type 1 Diabetes in 51 regions Worldwide (2008)
Conclusion: Incidence rates of Type-1 diabetes are generally higher at latitudes farther away from the equator where there is less UVB radiation necessary for vitamin D production in humans. Type-1 diabetes incidences decrease in regions closer to the equator.
Vitamin D and Diabetes (2005)
Note: Comprehensive article explaining how vitamin D deficiency contributes to diabetes.
Conclusion: A 30-year Finland birth-cohort study involving 10,366 children found that those who regularly took supplemental vitamin D had a lower risk of developing type 1 diabetes.
Use of Cod Liver Oil During Pregnancy Associated with Lower Risk of Type 1 Diabetes in the Offspring (2000)
Conclusion: Norway study examining 85 type-1 diabetic subjects and 1,071 non-diabetic controls found that mothers supplementing with dietary vitamin D during pregnancy resulted in their offspring enjoying a lower risk for developing type-1 diabetes.
Vitamin D Supplement in Early Childhood and Risk for Type I (Insulin-Dependent) Diabetes Mellitus (1999)
Conclusion: Vitamin D supplementation in infancy is associated with a decreased risk for developing Type 1 Diabetes.
Worldwide Increase in Incidence of Type 1 Diabetes: The Analysis of the Data on Published Incidence Trends (1999)
Conclusion: Meta-analysis of 37 multi-year and multi-decade studies tracking type-1 diabetes rates in 27 different countries found that, overall, incidence rates of type-1 diabetes are increasing 3% world-wide. Could the trend towards more indoor lifestyles (with less sun exposure and vitamin D) be contributing to this?
Conclusion: This study found hormonally active vitamin D to be extremely effective for reducing the prevalence of type-1 diabetes among NOD mice, a type of lab mouse intentionally bred to develop diabetes.