Again you may not find this relavent but here it is any way.
Beta Cell Dysfunction Begins at 2-hr OGTT Test Readings Over 100 mg/dl (5.6 mmol/L)
When a team of Italian researchers led by A Gastardelli started examining beta cell response to glucose in people with normal blood sugars, they discovered that a small amount of beta cell dysfunction began to be detectable in people whose blood sugar rose only slightly over 100 mg/dl on a 2-hour glucose tolerance test. The beta cells are the cells in the pancreas that produce the insulin your body uses to control your blood sugar.
Analyzing their data further, they found that with every small increase in the 2-hour glucose tolerance test result, there was a corresponding increase in how much beta cell failure was detectable.
Conclusion/
When the plasma insulin response to oral glucose is related to the glycaemic stimulus and severity of insulin resistance, there is a progressive decline in beta-cell function that begins in “normal” glucose tolerant individuals.
https://link.springer.com/article/10.1007/s00125-003-1263-9?LI=true