If memory serves around 4-6 mmols would be an 'acceptable' fasting blood sugar level. Slightly above that and there may be some impaired glucose tolerance. When it gets higher then diabetes is diagnosed.

Diabetics 'run' their sugars at different levels. Some a little higher dependant on activity, and control it with insulin (type I diabetes). Type II diabetes I know less about but a Google should tell you more. IO think they can control theirs more with diet.

mp