Alpha lipoic acid is an insulin mimetic. In other words it can stimulate the uptake of glucose from the blood by fat cells and muscle cells, much as insulin does, only to a lesser degree.
Some people find blood sugars are a little lower, and insulin doses can be reduced, if ALA supplements are taken. I tried it out a few years back but didn't notice any particular improvement, certainly not enough to justify taking oral meds every day.
All the best,
fergus