21st August 2018
One of the most common diseases in the world is type II diabetes, and it seems to be increasing inexorably. I feel I should quickly mention that I have a problem with calling a high blood sugar measurement a ‘disease’ but that is an issue for another time. Anyway, because type II diabetes also greatly increases the risk of CVD (by around 300 – 500% depending on which study you read) then I could hardly continue ignoring it, in a blog primarily focussed on CVD.
At present, the increase in CVD risk in diabetes is not explained by the widely accepted risk factors.
‘Patients with diabetes have increased vascular vulnerability to atherogenic insults, leading to accelerated atherogenesis. Although atherogenesis is in part due to the increased prevalence of traditional cardiovascular risk factors, these factors cannot fully explain the propensity toward vascular complications in diabetic patients.’1
This, in some ways, is a rather bizarre concept. Type II diabetes is a traditional risk factor for CVD. So why do we need to explain why a risk factor cannot be explained by other risk factors? Which, if you try to chase down the logic, provides a perfect example of the incoherence around the thinking on CVD.
Anyway, what is really meant here is that, whilst other conventional risk factors, such as blood pressure, are raised in diabetes (although not necessarily) most other ‘traditional’ risk factors are unchanged. LDL is certainly not raised, although there is usually a high VLDL/triglyceride level and a low HDL level. However, in my opinion – and the opinion of many others – the high VLDL and low HDL is a result of insulin resistance in the liver. It is not a cause of, anything2.
So, what causes the greatly increased risk of CVD in type II diabetes? What is the mechanism, or process going on here? You may be thinking to yourself, a high blood sugar must be damaging. Now that may well be true (although it could well be that a high insulin level is damaging, because you rarely find one without the other). But if a high blood sugar is damaging, how does it do the damage?
At this point I shall introduce you to the glycocalyx – never mentioned before on this blog. Not, I hasten to add, because I had never heard of it, but because it added another complication to the discussion so far. A complication that I felt was not needed. Now it is. Because you cannot explain how diabetes increases CVD risk without looking at the glycocalyx.
If you have ever tried to pick up a fish, you will find that it slips through your fingers. This is due to the slippery slimy layer that lies on top of the scales. This is glycocalyx, or at least the fish version of glycocalyx. It allows fish to swim faster, because the glycocalyx is almost frictionless.
Inside your blood vessels, and lining endothelial cells, we humans have a slippery, slimy layer that, under a powerful microscope looks like a billion tiny hairs. This is our glycocalyx. A slippery forest. It does many, many, different things. Yes, I know, the human body is just mind-bogglingly complicated.
What are these ‘hairs’? They are usually referred to as proteoglycans. Basically, long strands of protein and sugars bound together. You can look them up on Google images, if you wish. Lots of pictures to see.
Perhaps the best paper to read in this area is, the following: ‘Loss of Endothelial Glycocalyx during acute hyperglycemia coincides with endothelial dysfunction and coagulation activation in vivo.’ 3
Main functions of the glycocalyx:
- Protects the underlying endothelium from damage
- Maintains the endothelial barrier function
- Acts as a mechanical sensor for stress/shear stress
- Mediates nitric oxide (NO) release
- Anticoagulant (stops blood clotting) – many anticoagulant factors live here, including NO
- Prevents adhesion of white blood cells and platelets.
It should come as no surprise, therefore, that if you damage the glycocalyx, a number of very bad things are going to happen. Damage to the underlying endothelium, adhesion of platelets, loss of anticoagulation, severe disruption to nitric oxide synthesis etc. etc. And a high blood sugar level does ALL of these things.4
So, there you go. Diabetes/raised blood glucose greatly increases the risk of CVD by causing damage to the glycocalyx/endothelium, and a parallel increase in the risk of blood clotting. Which, as you may have noticed, is exactly the mechanism of action that I have been outlining on this blog for the last three years. And if you think it cannot be that simple. Well, it is.