In a recent article in Orthomolecular News states:
More than 460 million people, almost 6% of the world's population, are suffering from type 2 diabetes, the most common form. Over 1 million deaths per year can be attributed to this condition, which makes it a leading cause of death. And the number of new cases is constantly increasing worldwide. By 2030, more than 7% will be suffering from type 2 diabetes.
Besides lowering the risk of developing type 2 diabetes, vitamin D also helps to reverse the disease. In patients with type 2 diabetes and low vitamin D levels, supplementation with vitamin D significantly lowered blood glucose levels (fasting glucose level and long-term blood glucose value HbA1c) and improved insulin resistance.
Cofactors of vitamin D also have an important role in the prevention of type 2 diabetes. Deficiencies of magnesium and vitamin K2 are very common among the public with almost half of the US population having an inadequate intake of magnesium  and up to 97% of older people suffering from an insufficiency of vitamin K2.  Type 2 diabetes is associated with low magnesium levels,  and a high dietary intake of magnesium was associated with a lower risk of developing type 2 diabetes.  Also, magnesium supplementation helps treat prediabetes and type 2 diabetes, and significantly reduced glucose parameters and improved insulin sensitivity in such patients.  Type 2 diabetics have significantly lower vitamin K2 levels than healthy controls,  and supplementation of K2 significantly reduced glucose levels (fasting glucose and HbA1c) in patients with diabetes. 
The incidence of type 2 diabetes would likely be drastically reduced if all people could get adequate amounts vitamin D and its most important cofactors like magnesium and vitamin K2.
The author's conclusion is quite practical and straight-forward....manage your nutrient deficiencies, eat a low-carb diet and move your body:
The level of vitamin D and its cofactors magnesium and vitamin K2 are widely deficient in individuals throughout the world. These deficiencies attenuate the function of the body's immune system and contribute to widespread disease and death that could be prevented with adequate supplements. In many cases, type 2 diabetes can be prevented and reversed with a protocol of essential nutrients that includes vitamin D, magnesium, vitamin K2, and mild dietary restriction in a low-sugar diet with colorful raw and cooked vegetables. Many people including medical professionals are unaware of the problem and its solution. Please spread the word!
You can read the full article here.