Here’s a list of studies about vitamin D and type 2 diabetes:

Serum 25-Hydroxyvitamin D, Calcium Intake, and Risk of Type 2 Diabetes After 5 Years: Results from a National, Population-Based Prospective Study (2011)

Conclusion: A five-year study of 6,537 Australian adults found that those who developed diabetes had lower vitamin D levels.


Effects of Vitamin D and Calcium Supplementation on Pancreatic β Cell Function, Insulin Sensitivity, and Glycemia in Adults at High Risk of Diabetes: The Calcium and Vitamin D for Diabetes Mellitus (CaDDM) Randomized Controlled Trial (2011)

Conclusion: In a 4-month randomized control trial involving 92 prediabetic adults, those given 2,000 IU of vitamin D daily experienced improved pancreatic beta cell functioning.


Vitamin D and Type 2 Diabetes: A Systematic Review (2011)

Conclusion: A meta-analysis of 19 different studies investigating the association between vitamin D status and type 2 diabetes incidence found that those with higher vitamin D levels have a significantly lower risk (43% lower) of developing diabetes compared to those with lower vitamin D levels.


A Cross-Sectional Study of Vitamin D and Insulin Resistance in Children (2011)

Conclusion: A study of 85 Philadelphia children found that those with lower vitamin D levels have worse insulin resistance.


Role of Vitamin D in Insulin Secretion and Insulin Sensitivity for Glucose Homeostasis (2009)

Note: Comprehensive overview of the evidence demonstrating an association between vitamin D status and type-2 diabetes risk.


Vitamin D as an Analgesic for Patients With Type 2 Diabetes and Neuropathic Pain (2008)

Conclusion: A study of 51 vitamin D-insufficient type 2 diabetics with neuropathic pain found that three months of vitamin D supplementation was effective for significantly reducing pain in all of the patients.


Low Serum 25-Hydroxyvitamin D Concentrations are Associated with Insulin Resistance and Obesity in Women with Polycystic Ovary Syndrome (2006)

Conclusion: A study of 120 adult women found that those with the lowest vitamin D levels also had the highest body fat percentages and highest rates of insulin resistance.


Vitamin D Status and Glucose Homeostasis in the 1958 British Birth Cohort (2006)

Conclusion: 7,189 caucasian subjects from the 45-year 1958 British Birth Cohort were analyzed to find a possible correlation between amount of body fat, blood sugar levels, and vitamin D levels. The rate of vitamin D insufficiency was higher in the obese subjects (80%) compared to the others (68%) and those with lower vitamin D levels also had higher blood sugar. These results are in line much of the rest of the research that has been done showing that: vitamin D-deficiency promotes obesity, obesity also causes vitamin D-deficiency, and vitamin D-deficiency reduces glucose metabolism.


The Effect of Vitamin D3 on Insulin Secretion and Peripheral Insulin Sensitivity in Type 2 Diabetic Patients (2003)

Conclusion: In a control trial experiment involving ten vitamin D-deficient type 2 diabetic women and 17 same-age, same-weight, non-diabetic females, taking just 1300 IU of vitamin D daily was found to be effective for increasing vitamin D levels by 75% and decreasing insulin resistance by 21%. “ We suggest vitamin D3 deficiency may at least partly contribute to the impairment of insulin secretion and probably of insulin action. Our results suggest that vitamin D3 supplementation could be an element in the complex treatment of type 2 diabetes.”

(Editor note: 1300 IU is an extremely low dose of vitamin D for an adult. Imagine what effect 5,000 – 10,000 IU daily would have on insulin resistance. Or more….)


Diabetes Disparities Among Racial and Ethnic Minorities (2001)

Note: Article detailing how dark-skinned people suffer disproportionately from type 2 diabetes (2-6x more than white people) and it’s related complications. Could this be due to the well-documented increased difficulty of dark-skinned people to produce adequate vitamin D from sun exposure?


Inadequate Vitamin D Status: Does it Contribute to the Disorders Comprising Syndrome ‘X’? (1998)

Conclusion: Pancreatic islet cells contain vitamin D receptors, vitamin D plays a vital role in proper insulin functioning, and those who are vitamin D deficient are at an increased risk for diabetes.


Hypovitaminosis D is Associated with Insulin Resistance and Beta Cell Dysfunction (2004)

Conclusion: Of 126 healthy subjects, those with higher vitamin D levels tended to have higher insulin sensitivity and faster insulin response. Those with lower vitamin D levels tended to have deteriorating beta cell function, higher blood sugar levels, and an increased risk for and prevalence of metabolic syndrome.


Improvement in Glucose Tolerance and Beta-Cell Function in a Patient with Vitamin D Deficiency During Treatment with Vitamin D (1994)

Conclusion: A 65-year-old vitamin D-deficient, hypocalcemic woman with osteomalacia was treated with 2000 IU of vitamin D daily over a 5-month period. Her glucose metabolism and beta cell function were also observed over the course of the treatment. The first month both her glucose tolerance and beta cell function showed immediate improvement and this continued on for the entire five months. “Improvement in beta-cell function and consequently in glucose tolerance is likely to have been due to correction of hypocalcaemia, vitamin D deficiency and secondary hyperparathyroidism.”


Vitamin D and Calcium Intake in Relation to Type 2 Diabetes in Women (2006)

Conclusion: 83,779 adult women from the long-term Nurses Health Study (started in 1976 and involving 121,700 female subjects) were analyzed for a relationship between vitamin D and calcium intake and type 2 diabetes risk. Over the course of 20 years, 4,843 cases of type 2 diabetes were found. Women who consumed more than 1200mg of calcium and more than 800 IU of vitamin D daily had a 33% lower risk for type 2 diabetes compared to women who consumed less than 600mg of calcium and 400 IU vitamin D daily. Women with higher vitamin D and calcium levels have a lower risk for diabetes. Women with lower vitamin D levels have an increased risk for diabetes. “The results of this large prospective study suggest a potential beneficial role for both vitamin D and calcium intake in reducing the risk of type 2 diabetes.”


The Role of Vitamin D and Calcium in Type 2 Diabetes. A Systematic Review and Meta-Analysis (2007)

Conclusion: There is a relationship between lower vitamin D and calcium levels and risk for type 2 diabetes. “Vitamin D and calcium insufficiency may negatively influence glycemia, whereas combined supplementation with both nutrients may be beneficial in optimizing glucose metabolism.”


Vitamin D and Diabetes: Improvement of Glycemic Control with Vitamin D3 Repletion (2008)

Conclusion: In two different case studies of vitamin D-deficient type 2 diabetic women, supplementing with 2,000-3,000 IU of vitamin D daily improved vitamin D levels and blood glucose levels after 6-9 months.


Serum 25-Hydroxyvitamin D3 Levels Decreased in Impaired Glucose Tolerance and Diabetes Mellitus (1995)

Conclusion: “We conclude that diabetes and IGT [impaired glucose tolerance] are associated with low serum concentrations of 25-hydroxyvitamin D3 [vitamin D].”


Vitamin D, Adiposity, and Calcified Atherosclerotic Plaque in African-Americans (2010)

Conclusion: A study of 340 black adults with type 2 diabetes found that those with the highest percentage of body fat also had the lowest vitamin D levels and the highest amount of carotid artery and aorta plaque. There is a correlation between high body fat and low vitamin D levels and a correlation between low vitamin D levels and increased risk for atherosclerosis.


Vitamin D3 Improves Impaired Glucose Tolerance and Insulin Secretion in the Vitamin D-Deficient Rat in vivo (1986)

Conclusion: Read the title.


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