From Hypovitaminosis D is associated with insulin resistance and β cell dysfunction, 2-hour post-load blood glucose level in an oral glucose tolerance test (OGTT) has a negative correlation with 25(OH)D concentration (Fig 1C). 25(OH)D concentration has a positive correlation with insulin sensitivity (Fig 2A). Therefore, 2-hour post-load blood glucose level in a OGTT has a negative correlation with insulin sensitivity.
"Extrapolation from the observations in the current study suggests that increasing 25(OH)D from 10 to 30 ng/mL can improve insulin sensitivity by 60%, from 3.8128 to 6.1176 (umol/L)·m-2·min-1·(pmol/L)-1. This improvement in insulin resistance could potentially eliminate the burden on cells and reverse abnormal glucose tolerance. Furthermore, the 60% improvement in insulin sensitivity that results from vitamin D treatment indicates that that treatment is more potent than either troglitazone or metformin treatment (54% and 13% improvement in insulin sensitivity, respectively). The modest effect of vitamin D on insulin sensitivity in individual persons may translate into a dramatic effect in the population as a whole because of the high prevalence of hypovitaminosis D, which, in a large population, carries an attributable risk for type 2 diabetes and the metabolic syndrome. Although a review of the literature suggests non-calcium-mediated effects, the underlying molecular mechanism remains to be elucidated."
As my 2-hour post-load blood glucose level in a OGTT became low (3.7mmol/L, from 8.7mmol/L in 2003) after supplementing with 5,000iu/day of Vitamin D3, this means that my insulin sensitivity became high. Therefore, I cured my pre-type 2 diabetes using supplements.
My fasting blood glucose level also fell from 6.8 mmol/L (> 7.0mmol/L = type 2 diabetes diagnosis) to 5.0mmol/L. I achieved this without taking any drugs for type 2 diabetes - not even Metformin, which I consider to be a safe & effective insulin-sensitiser, though it can cause gastric distress and B12 absorption issues, long-term. The supplements that I took had zero side-effects and merely corrected deficiencies.
Diabetes drugs cannot cure type 2 diabetes. However, supplements & exercise can cure type 2 diabetes, if the type 2 diabetes is caused by nutrient deficiencies and/or sedentary behaviour and if all pancreatic beta cells haven't been destroyed. Insulin injections can preserve pancreatic beta cells, while insulin resistance is being tackled. See Dr. Richard K Bernstein on insulin for type 2 diabetics, and some definitions.
Sadly, if there are no nutrient deficiencies and/or all pancreatic beta cells have been destroyed, supplements & exercise will not help.