I believe it's important for everybody to be mindful of their blood sugar levels, not just diabetics who I used to treat. Either high or low blood sugars can cause their own set of problems, which is why a healthy and balanced diet is essential.
Insulin is the hormone that controls blood sugar levels. Vitamin D may improve the function of pancreatic cells that make insulin and increase your body's responsiveness to insulin.
High blood sugar can destroy cognitive function - but equally low blood sugar levels can affect mood. If you have insulin resistance, one is not able to absorb amino acids into the cells and then it's more difficult for the body to make neurotransmitters like dopamine, GABA or serotonin that control mood, including levels of anxiety and depression.