Choi et al1 found an inverse relationship between dairy consumption and incidence of type 2 diabetes mellitus. They looked at various possible factors to explain this including the lifestyle of dairy consumers, body mass index of dairy consumers, electrolytes, and the glycemic load of milk. Another factor may be worth considering.
Inadequate levels of vitamin D are associated with metabolic syndrome.2,3 Chiu et al2 found a positive correlation between levels of 25-hydroxyvitamin D and insulin sensitivity. Metabolic syndrome is a risk factor for type 2 diabetes mellitus.4
Ross CM. Dairy, Vitamin D, and Type 2 Diabetes Mellitus. Arch Intern Med. 2005;165(20):2434. doi:10.1001/archinte.165.20.2434-a