Zinc supplementation improved insulin resistance, inflammation, and oxidative stress in people with diabetes or prediabetes, even though it didn't clearly lower blood glucose.
This fits with the biology of zinc. Inside the pancreas, it helps insulin molecules assemble into compact structures so they can be safely stored and released when blood glucose rises. Zinc also supports insulin signaling and antioxidant defenses, both of which can become disrupted in diabetes.
This doesn’t mean everyone should supplement. Any benefit may depend heavily on whether someone is getting enough zinc in the first place, while excessive zinc intake carries risks of its own (like interfering with copper absorption).