While vitamin D supplements may offer a slight benefit for blood sugar control, taking then isn't the most effective way to significantly improve glucose levels. How Might Vitamin D Improve Blood Sugar Control? Notably, prediabetes has been linked to low levels of vitamin D.Research examining how vitamin D supplementation may affect prediabetes has shown some promise, said Roxana Ehsani, MS, RD, CSSD, a sports dietitian. It’s also unclear if there are any adverse long-term effects of taking vitamin D supplements. Should People With Prediabetes Take Vitamin D for Blood Sugar Support?