Deficiency of vitamin D is linked to reduced insulin secretion and increasingly reported in type 2 diabetes mellitus in epidemiological as well as experimental studies. A trial of animals demonstrates that 1,25 dihydroxy vitamin D regulates the β cell of the pancreas for secretion of insulin. A connection between resistance of insulin and deficiency of vitamin D is influenced by presence of inflammatory marker is linked with vitamin D deficiency. Vitamin D genetic mutation may predispose to type 2 diabetes and glycemic control. Epidemiological studies demonstrated a link between 24-hydroxyvitamin D3 low-level serum amount and increased risk of type 2 diabetes and metabolic syndrome, which an increase in fat mass may partially describe. A possible normal relationship linking with type 2 diabetes and vitamin D deficiency should be verified by a randomized clinical trial demonstrating that either vitamin D supplements may improve insulin resistance and insulin sensitivity or prevent type 2 diabetes. The result of randomized controlled trials (RCT) on an impact of placebo versus Vitamin D, occasionally combination with calcium and prediabetes. Review of available studies demonstrated decreased in glucose fasting plasma or improved insulin resistance. Meta-analysis of RCT does not show a significant effect on glycemic control by vitamin supplementation. Nowadays, a large RCT is performed for a high dose of vitamin D to control glycemic control. The deficiency of vitamin D needs to be regulated or prevented; until then, no vitamin D supplementation should be recommended to avoid type 2 diabetes.