This is the question that someone in the audience asked at the end of a presentation on diabetes that I attended a few months ago. Remarkably, the speaker was unable to answer this question. Amazingly, neither could any one of the three medical doctors that were in attendance. I was, naturally, quite shocked by this obvious display of ignorance on all of their part. At the same time, I wasn’t really surprised, and, in fact, relieved to be vindicated in my belief that probably the majority of MDs don’t understand the most basic things about human physiology and metabolic function.
Now, you, on the other hand, you who has been following and reading this blog, might (or even should), I believe, be able to answer that question. But since you’re reading this, and therefore cannot be put on the spot, as was the speaker and those MDs at that presentation, you don’t have anything to worry about if you can’t. And yes, I am going to explain. On top of that, I’ll be as quick as I can about it.
As always, first things first: How is blood pressure regulated? What is it that does the regulating? And why is it important?
Blood pressure regulation is of the utmost importance for the proper functioning of every organ because every cell in the body depends on a properly functioning circulatory system to bring nutrients and carry away waste. Blood pressure is like the voltage that drives current through wires and electronic components: it is a driving force. And exactly like it is for electric and electronic devices, the driving force must be just right: it cannot be higher and it cannot be lower than what it needs to be in every moment depending on what the immediate circumstances and needs happen to be. Therefore, blood pressure regulation is essential for the moment to moment adaptation of every metabolic and physiological function, to the different activities we do, and circumstances we find ourselves in.
The main organ responsible for blood pressure regulation is the kidney. I use the singular because the two kidneys work in the same way. It’s just that their function is so vitally important that there are two of them, most logically for redundancy, as a fail-safe system. I have written at length about kidney function in two articles entitled The kidney: evolutionary marvel; and How much salt, how much water, and our amazing kidneys. By the way, this is what I meant earlier: if you’ve read those, understood and happen to remember a few essential bits, then you would be in a good position to answer the question as to the relationship between diabetes and blood pressure. Here it is in a few words; well, maybe a few paragraphs.
The kidney’s vital role is filtration of metabolic acids out of the blood, and elimination of these through the urine. To do this as best it can, because the first and most important part of the filtration process relies on the separation of the liquid from the solids in the blood, and because this is done through what is a mostly “mechanical” filtering through a membrane as it is in water filters, the kidney must maintain optimal pressure to ensure optimal function of the little filtering units, the nephrons. If pressure is too low, the membrane filtering does not work well. If pressure is too high, the membrane tears or pops, and the filtering units stop working altogether.
The good news is that damaged nephrons can sometimes recover when the conditions are made conducive to it, and that there are millions of them in each kidney. The real bad news is that when they die, they do not come back to life. Another bit of bad news, although some would surely take this as good news instead, is that this process of deterioration of kidney function and death of nephrons takes place gradually but silently over the years and decades of our life. When the consequences of poor kidney function become noticeable or even critical, and we finally go see our MD because we’re not feeling good, or worse, are brought directly to the emergency room, it is far too late, for most of the nephrons are already dead.
And to be perfectly clear on this, if the kidneys fail and we don’t get immediate attention and artificial filtering of the blood through dialysis, we die within hours. This is what is meant by the word vital when qualifying the kidney as such an organ.
As I often highlight, the cells, tissues and organs that constitute the entirety of the body that we erroneously call ours and mistakenly believe this to be the case, do not care about you in the least. They do not know anything about you and never will. They, as all living things, are only concerned with survival and self-preservation. It is for this reason that they continually adapt in all sorts of ways to the environment in which they find themselves: this is the internal environment of the body. And it is for this reason that the kidney regulates blood pressure so accurately and so well when allowed to function as it should.
How does it do this regulating? By very closely monitoring the concentration of the blood and secreting hormones to induce the necessary adjustments. The concentration of the blood is the balance between the amount water and the amount of solutes (things dissolved in the water). Most important is the amount of water, because it gives the blood its volume and thus pressure within the closed circulatory system of somewhat malleable veins and arteries. Of the solutes, the most important is sodium, because it holds and must be held in the highest concentration of all solutes, accounting for about half of the overall solute concentration (140/300 mOsmol/L). But the kidney works to keep the entire spectrum of natural solutes, especially the minerals, each in its optimal physiological range.
Two nutrients that the kidney works to keep in circulation are proteins and glucose for the obvious reason that they are essential to proper physiological function, and, evolutionarily speaking, rather rare to come by and thus precious. As they are also solutes circulating in the blood plasma, each contributes to the total concentration. And this is where we get to the point:
As glucose concentration rises, the total concentration of the blood rises accordingly. For insulin-resistant diabetics whose cells have lost their sensitivity to insulin, and with that their ability to take up glucose from the blood, there is no outlet for this excess glucose that just keeps on rising in concentration. But unlike what the kidney does in regulating the concentration of sodium and other minerals by excreting any excesses through the urine, glucose is kept in circulation, as much as possible.
After some time, whether because the concentration is through the roof, because the kidney cannot anymore function as it should to keep the glucose in the blood, or both, glucose spills into the urine. This is how, in fact, it was discovered that all of the symptoms that we described as the condition of diabetes are due to a dysfunctional metabolism of glucose: because the urine of diabetics was sweet smelling and sweet tasting. (What dedicated MDs we had 100 years ago! Do you think your MD would taste your piss today to make sure you’re not sick?).
In response to this, to maintain the concentration as close to 300 mOsmol/L as possible, the kidney retains water to dilute the blood from the excessive glucose. This makes the blood volume increase and therefore also the blood pressure. This is why diabetics have high blood pressure. This is also why diabetics have very high incidence of kidney disease. This is also why diabetics have water retention and circulatory problems.
But this is also why they suffer from a lot more strokes, heart attacks, Alzheimer’s, dementia, arthritis, why they have elevated cholesterol, why they age so much faster, and why they go blind.
Chronically elevated glucose leads to chronically elevated levels of glycation. Glycation damages cells and tissues everywhere in the body, but firstly in the veins and arteries, which are already significantly more susceptible to damage because of the chronically elevated blood pressure. This leads to more and faster plaque formation, as well as cholesterol production for damage control and repair. Elevated glucose levels and heightened glycation lead to a flood of free radicals and vastly increased systemic inflammation, which makes everything worse, much worse.
And all of these conditions, all stemming from insulin resistance and chronically elevated blood sugar, give rise to the multiplicity of the health problems just enumerated that are the main causes of death in the general population, but which are seen with an approximate three to four fold increase (that’s 300-400% more!) in incidence for a given age in the diabetic population.
What about non-diabetics? Do they need to be concerned about this? Does it mean that there is a direct relationship between blood sugar and blood pressure in all of us? Does it mean that all of us suffer from the whole lot of direct and indirect consequences of having high blood glucose concentrations in the same way as diabetics do, but in proportion to the concentration and the time it takes for it to drop depending on insulin sensitivity? What do you think?
Is any of this surprising? Not in the least: it makes perfect sense. Is it difficult to understand why it happens? Not really: when we understand some basic physiology and biochemistry, everything becomes relatively easy to grasp and explain. At least that’s what I hope I was able to show here, and at the very least, in regards to the question posed in the title that we set out to answer in the first place. You got it, right? And you’ll remember? And next time you see your MD, (if you have one, that is), ask them why diabetics have high blood pressure, and see what they say…
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