Reflux is a muscle sphincter issue... not something that can be resolved with vitamins. Stomach acid makes it way past that muscle into the esophagus.
Diabetes is when the body does not produce or properly use insulin. Insulin is a hormone that is needed to convert sugar, starches and other food into energy your body can use.
In short, there are real issues going on for the issues you ask about that require medication to deal with them properly. There is no miracle cure by use of vitamins alone... except maybe when dealing with cholesterol. Niacin (vitamin B3) in high dosed is proven to reduce cholesterol. High doses of other vitamins have not been a proven help with other deseases... however, many may help as a supplement for deseases.
Best of luck.