The DCCT and UKPDS showed that higher than normal blood sugar levels are closely related to the microvascular complications (e.g. retinopathy, kidney disease, neuropathy). The evidence (especially in the case of the DCCT) is overwhelming.
But the evidence that other complications of diabetes (especially heart disease/cardio issues) are related to high bg’s, is not so crystal clear. There’s some relation, but even the best controlled diabetics still die at alarmingly high rates from those complications.
So I think it’s clear that diabetes (both Type 1 and Type 2) is more than just a disease of blood sugars. The blood sugar is part of the diagnosis criteria but really there’s more. In the case of Type 1 there’s a predecessor autoimmune problem before the diabetes came along; in the case of Type 2 there’s other biochemical issues too.
Now that doesn’t mean that we shouldn’t try hard to manage our bg and all our other cardio risk factors. In fact I think it means that we should try harder.
My doc told me, when I was diagnosed 30 years ago, that if I took real good care of myself that a lot of diabetics lived for 20 or 25 years after diagnosis. Well, here I am at 30 years after diagnosis. And that’s not because I slacked off or waited for somebody else to cure it.