In the context of kidney disease, phosphorus is often discussed only as a problem, even though its role is far more complex. In this post, we walk through why phosphorus is essential for life, when it becomes a risk factor, and why the source it comes from makes a real difference. The video helps clarify the connections between diet, kidney function, and cardiovascular health.
The content of the video in written form
Hello, this is Zsom.
Dear patients, when we talk about phosphorus at the nephrology clinic or in the dialysis unit, then it comes out as something bad, something that is going to destroy your bones and blood vessels. Well, if we really think about this, nothing could be further away from the truth, because the actual truth is that phosphorus is a key player in many of the basic functions of the human body.
It is essential for bone structure. For instance, we can see here that much of the human or animal bones are composed of phosphorus in the form of phosphate, which is a kind of phosphoric acid. It is a major component of bone structure.
But not only that, phosphorus is a part of adenosine triphosphate, a molecule that is necessary for all energy-requiring processes in the body. So it functions as a universal energy currency throughout the body. ATP is very important in terms of enzyme function. It is very important in terms of all functions in various organs that require energy. Now, ATP is normally produced in cells within mitochondria, which are presumably of bacterial origin, and they have the basic function of producing energy that the cell then uses for all kinds of things. So in other words, ATP is released from mitochondria, and then it is distributed throughout the body.
And so this ATP is used, for example, for muscle contraction. So whenever your muscle contracts, or even when it relaxes, it uses ATP. It is the same with cardiac tissue. The heart muscle also needs ATP for both contraction and relaxation. In nerve cells, for proper functioning of nerves and the propagation of the nerve electrical activity, it is very important to have ATP on board. But also, just for basic enzyme function, it is very important to have phosphorus bound to various proteins that then function as enzymes. So without these bound phosphorus parts, the protein does not have a proper function for it to function as an enzyme. The same is the situation with lipids. For cell membranes, proper function is based on proper structure, and this structure is impossible without the participation of phosphorus.
But in terms of DNA and RNA, you also have a phosphate group on the nucleotides that form DNA and RNA. So you cannot have normal DNA and DNA function without phosphorus. Now, since we’ve talked about mainly the kidney here, we have to recognize that for any kind of organic acids in the blood to be removed, if they are in excess, then you need phosphoric acid for that. Phosphoric acid will give the kidney an opportunity to remove acid from the body. But also, for normal functioning of kidney cells in general, you need ATP, and without ATP, the kidney cells would cease to function.
So from this, you see that phosphorus is extremely important, and it is very important to understand that anything that is important for the body will be very closely regulated, and regulated at multiple levels, right? So normally, phosphorus intake is in the form of dietary intake. In other words, you eat something and there is phosphorus in it. And so what happens is that there is a vitamin called vitamin D that helps regulating phosphorus absorption through the gut. So here is your dietary phosphorus, and somebody, you know, calculated that on average you eat about this much phosphorus. But out of this phosphorus, only part is absorbed through the gut into the blood, and part of it is then removed.
And this absorption process is closely regulated, for instance, by vitamin D. Now, excess phosphorus is removed by the bowels and by the urine. And here, I’m going to emphasize something extremely important, and that is that the kidney is a very highly adaptable organ. So the kidney can sense how much phosphorus you need in the blood, how much phosphorus is in excess in the body, and the kidney then will remove whatever is not necessary. And the kidney can do this at a very high range. So in other words, if you have a lot of excess phosphorus, the kidney will remove that, because the kidney can sense how much this excess phosphorus, not needed phosphorus, is.
However, absorption does not only depend on vitamin D. There are a whole bunch of other factors that influence this process. For instance, bacterial flora. You see, when your gut is healthy, it maintains a stable bacterial flora. And you need that health, that healthy flora, for the absorption of phosphorus to be what it should be. And also, on the other hand, phosphorus absorption is going to be very dependent on what kind of food you eat, because phosphorus is bound to some degree within the structure of the food. And so the more strongly it is bound, the less easy it is to be absorbed through the gut.
Let’s take an example, an extreme example. If you have any kind of soft drink, you are likely to consume phosphorus in terms of phosphoric acid, in the form of phosphoric acid, that is very very often a component of the soft drink. So what happens is that here phosphorus is dissolved in water. So we call this inorganic phosphorus. And so whenever phosphorus is dissolved in something, then it is very easy to absorb it. So what happens is the same thing that happens with fructose glucose syrup. In other words, you have a huge sudden phosphate load, such as you have a huge glucose load in terms of dissolved fructose and glucose. You have a huge phosphorus load in terms of phosphate or phosphoric acid. And whenever something is this sudden, then the human organism has some difficulty handling that.
So we know that all humans are created equal, and that is true, but almost nothing else in nature is. If you look around between phosphorus and phosphorus, there are huge differences. And let’s first be clear about what type of foods have phosphorus in them, and what kind of phosphorus it is. Well, we already talked about inorganic phosphorus. Inorganic phosphorus is dissolved in water in soft drinks, but it is also present in food additives. For example, phosphate additives are very often added to bakery products to make them look more beautiful. So this is what we call inorganic phosphorus. And inorganic phosphorus is readily absorbed through the gut, because it’s not bound very much within the food structure or the drink structure.
So then you have organic phosphorus, which is found in dairy or found in meat. So you see meat, such as red meat or poultry, and dairy or eggs or seafood. All of these contain a high amount of organic phosphorus. Organic here means that they are more closely bound to the structure of the food. For example, poultry, meat, dairy, eggs, seafood, all have proteins. And these proteins then bind phosphorus so that it’s a little bit more difficult to absorb these. Now, in meats in general, this bound amount of phosphorus may be a little bit higher than in dairy, for instance.
But here comes the main difference. If you eat phosphorus from plants, in other words, foods that derive from plants, the situation is entirely different. And the reason for that is what we call phytic acid, which is very abundant in plant-based products. And so what happens is that phytic acid closely binds phosphorus, so it is much less absorbed through the gut. So then you have a situation when you can eat a relatively larger amount of protein, plant protein, and yet your phosphorus is not going to be totally absorbed. And here we have beans, nuts, legumes, seeds, and soy, which belong to this category of plant-derived protein-containing foods.
So then, the utilization of phosphorus depends on the functional state of the bones, the presence of adequate amounts of vitamin D, the presence of organic acids in the blood, the state of the blood vessels, and the presence of other hormones, including parathyroid hormone. Well, let’s go through these one by one. When you are forming bones, then phosphorus is going to be consumed by this process. So the phosphorus goes inside the bone structure. Now, if you, for instance, have a situation when your bone, because of presence of acids, for instance, or some kind of disease, is being absorbed, so in other words, you have destruction of bone structure, that phosphorus comes out of the bone, and so you will have a lot of unnecessary phosphorus in the blood.
Formation of the bone is very highly vitamin D dependent, so you cannot form bone without vitamin D. Well, the active form of vitamin D is largely produced in the kidney, so proper kidney function is very necessary for proper bone formation. But if you have kidney failure, then this vitamin D effect is going to be less, so you have impairment in bone formation, and you also, to some degree, have a decreased bone phosphorus absorption through the gut as well.
In advanced kidney failure, however, the main problem is not even this. The main problem is that because the kidneys, in general, function less, therefore their capacity to remove unnecessary phosphorus is going to be impaired. So here what you have is that phosphorus is going to accumulate in your body. Now, this usually happens only in advanced kidney failure. So what happens is that when your kidney failure is still kind of medium degree, then what happens is that there is a gland in the body called the parathyroid gland beside your thyroid right here, and they produce a hormone called parathyroid hormone, and this parathyroid hormone is trying to make the kidneys remove more phosphorus, you see, and this is all good, and for a time it works. However, the problem is that parathyroid hormone is going to have side effects, and we’re going to talk about these side effects, but let me just mention here that one of the side effects is bone resorption, so that you have phosphorus coming out of bone, and bone structure is going to be weaker.
And also, if you have problems with your blood vessels, then phosphorus is going to precipitate here, making your blood vessel walls rigid. So it’s really not a good idea to have a very high degree of parathyroid hormone production. So again, parathyroid hormone, or PTH for short, has these side effects of bone resorption, and it increases phosphate and calcium in the blood. But also, other substances accumulate in kidney failure, including something called FGF23, that inhibit vitamin D conversion in the kidney cells, and what happens then is that you have a decrease in gut calcium absorption, and that stimulates PTH, and remember, PTH has all these side effects, so that you have a weak and sometimes achy bone, you have then a relatively high phosphoric acid level, you have less effect of vitamin D, and so all what this does is that the excess phosphorus, provided that your blood vessels are not healthy, are going to precipitate in the blood vessel walls.
Now, phosphate retained because of kidney failure, combined with phosphorus released from the bone, precipitates in blood vessel walls, and it’s important to understand that this makes the blood vessels rigid, and therefore, blood pressure is high, blood pressure will become higher. Blood pressure is a product of how rigid your blood vessels are, especially if you have a lot of extra salt and water in your body. So the blood vessels cannot compensate, because they are rigid, and if they are rigid, your blood pressure is going to be immediately very high, if you have even a little bit of extra salt and water in your body.
So this process is dependent on the state of the blood vessels, because in kidney failure, what happens is that you have what we call uremic toxins, these are poisons that gradually accumulate in your blood, and especially the uremic toxins that are produced in the gut, they harm your blood vessels. Now, here comes the problem. If you eat and drink too much, you have hypervolemia, hypervolemia means that you have too much fluid and too much salt in your body, then not only that your blood pressure goes up high, but also hypervolemia makes your gut less healthy, it disrupts the normal gut function and the normal gut flora, so you’re going to have more of these uremic toxins, and this will then impair the function of your blood vessels even more, so you have a vicious circle here. So then phosphorus, salt, and water all cause phosphorus and calcium precipitation, making your blood vessels that are already not normal, even more abnormal, rigid, and your blood pressure is going to be high.
So with all of these problems, what is it that we see in terms of what happens, what actually happens to patients? Well, the combined effect of high phosphorus levels, altered hormone function, and vascular damage causing inflammation, you see, whenever you have repetitive damage of anything, it will produce inflammation, so we said that because of abnormal gut flora, because of abnormal amounts of salt and water retained by the kidney, and because of high phosphate levels, you have damage in the wall of the blood vessel. So since this damage is repetitive, it’s going to cause inflammation inside the blood vessels. And so this inflammation will then make it easier for phosphorus and calcium to precipitate even more in the blood vessels, so basically you have an accelerated aging of blood vessels. They become rigid, like in old age in general, but at a much earlier stage in life.
So what you see here is that you have the age of the patients in years, and you have the risk for dying early. And so what you have in a normal population, that is without kidney failure, is then that mortality, so the risk for dying, is going to be a function of age, right? So if you are very young, you are very unlikely to die of cardiovascular disease, whereas if you are old, then this risk is very high. But if you are a kidney patient, and especially a patient on hemodialysis, then what you see is that this function almost completely disappears. Sure, there is some difference between old dialysis patients and young dialysis patients, but this difference is much less than the difference here. So what you see is exactly this, that you have an early aging, a premature aging of blood vessels, which then result in a high degree of mortality, risk of dying.
So you might know, if you are a kidney patient, that for cardiovascular disease, for example myocardial infarction, or stroke, or whatever, you have certain risk factors, such as smoking, diabetes, hypertension, cholesterol, high cholesterol levels, etc., you know, lack of exercise, and others.
However, in terms of kidney disease, you have a different set of risk factors, even in young people. Let me just enumerate at least some of these. So one is that you retain salt and water, right? With that, you basically decrease the normal gut flora, and this abnormal gut flora is going to damage your blood vessels by producing these poisons that go into the blood.
Then, you have vascular inflammation, that is inflammation of blood vessels. And whenever you have this inflammation, then phosphorus and calcium are going to precipitate, making the blood vessel walls very rigid. And in terms of risk factors for cardiovascular disease, those patients that are not yet on dialysis, one of the major problems is going to be proteinuria, the amount of protein in the urine, which is kind of a marker for all of these processes.
So what happens is that, in chronic kidney disease, high phosphorus, among other things, is going to correlate with cardiovascular mortality. So what we see here, that high phosphorus increases the risk of dying from a heart condition. But again, see that all these other things also influence this process.
Now, if we pick out one thing out of many, and we only concentrate on the association of high phosphorus and cardiac death, then here is what we are going to get. So yes, there is an association between high phosphorus and mortality. But when we try to lower phosphorus, then everything remaining equal, what we see is that, first of all, when we introduce diets to decrease phosphorus, we are not very successful. So when we introduce a low phosphorus diet, then phosphorus in many patients remains high. And even if we manage to lower phosphorus through a low phosphorus diet, then what we see is that this diet is not going to increase survival. That’s interesting, isn’t it? So no wonder that large international surveys show that diet in itself is largely ineffective in advanced kidney disease, both in terms of lowering phosphorus and lowering death rates.
On the contrary, what these surveys show is that when you have a low to normal phosphorus in advanced kidney disease, you tend to identify patients whose appetite is low. And they are relatively malnourished, they don’t eat enough. So what you see here is diet is not a solution, really, at least in itself. And if you try to lower phosphorus with diet, well, you know, you are not going to get much of a success.
Well, then, if that is the case, well, we have another approach. We identify that there is an association between high phosphorus and dying of heart disease. So we are trying to decrease phosphorus through medications, right? These are the so-called phosphate-binding agents. And there are all kinds of phosphate-binding agents. For example, calcium-based, magnesium-based, iron-based, lanthanum-based. So what they do is that they bind phosphorus in the gut, so the absorption of phosphorus through the gut into the blood is reduced. And very often, at least to some degree, these medications actually work, and they lower phosphorus. Yet, when the phosphorus is lowered due to the action of these medications, you see that you really did not improve survival.
Hmm, I wonder. So what is the solution? Well, here it helps very much if your doctor is not only a scientist, not only a physician, but also a philosopher. Because philosophers tend to understand associations and complex systems that scientists don’t always. So remember what I said about phosphorus. That when we investigated the relationship between high phosphorus and cardiovascular mortality, the chance of dying from a heart condition, then we picked out phosphorus as if it was a major player in itself.
Well, scientific studies establish associations, not causation. So if something is associated with something, that does not mean that this something caused this something. It could be just a marker. It could be a signal that something is happening in the background. And therefore, phosphorus is not the only problem. It’s just signaling something else.
Now, the other issue is that whenever you do a scientific study, then you do that scientific study in specific populations. So your situation as an individual might be different than the average of those specific populations, right? So what happens in people who did the study may not be happening in you.
So let’s put this in perspective. Yes, high phosphorus is associated with death, but it may not in itself cause death. It is partly a sign of something else that is going on in the background. For instance, high phosphorus may be a sign that you are not eating the right things. So if this is part of the equation, then let’s investigate if this actually is the case. So what do you see here? That this thing, which contains phosphoric acid, also contains other things. Things that, for example, preservatives, food coloring agents, different other kinds of acid, fructose and glucose syrup, may also directly influence your heart and blood vessels, right? So phosphorus is going to be high, but yet it may not be phosphorus itself that is causing the problem, but everything else that comes with it.
And so if you look at bakery products, then you see that besides phosphorus, you have all these fatty acids, which are very unhealthy. Especially saturated, hydrogenized forms of these lipids, these fats, are going to be very bad for your blood vessels. So then, we conclude that scientists are wonderful in conducting studies, but the interpretation of the studies is not always entirely of a wide perspective. You focus a little too much on these things. So you might need a philosopher-scientist to help you interpret these results using logic. Because philosophers have a wider perspective, and they are more used to use logic with a wider perspective.
And so, the logical solution in this particular situation is that reducing high phosphorus in itself is not enough. You also need to see what comes as a package together with high phosphorus. So for instance, your diet. It may just be that you identify with a high phosphorus level individuals with poor diet. So for instance, if somebody takes phosphorus in with a high amount of soft drinks, that is really not healthy for you for other reasons, then, of course, high phosphorus is going to be correlated with heart problems. Oh, by the way, this is a younger version of me, actually, at the nephrology clinic.
So now it becomes easy. You see, when you have soft drinks or pizza or chips which contain a high amount of phosphorus, they also contain salt, glucose, fructose syrup, phosphoric additives, food additives, and therefore, they are just not going to be good for you. So when you eat phosphorus, more like plant-based proteins, like this lentil soup here or this type of plant-based product or this, then you are going to get a high amount of very good proteins and relatively, with respect to and in comparison to how much good things you eat, relatively less amount of phosphorus since it’s going to be absorbed a little less.
You have a lot of good things at the expense of a little bad thing. And here comes the issue. You see, besides exercise, of course, chocolate is one of the very few things that in dialysis patients is known, is proved to improve survival, chances for survival. So chocolate is very good. And yet, they are going to tell you that phosphorus will prevent you from eating chocolate because it has a high amount of phosphorus. And so walnuts also have a high amount of phosphorus. But it also has an overall effect of protecting your blood vessels. So now you see that you have to make place for these things, at least a little bit of these things.
So let us create space for quality foods by eliminating junk food. And I propose a new concept. And that is the phosphorus over good food ratio. So you need to take in phosphorus with good food, which has a lot of good nutrients that are necessary for your body. And not taking in unnecessary foods that contain, in addition, other things that actually harm your body, gives you the space to eat quality foods. So given the amount of phosphorus absorbed versus the healthy effects of food involved is going to be the background of this phosphorus over good food ratio. So P over G. And this P over G ratio is going to be close to zero, even negative, if you take in your phosphorus as soft drinks, as junk food. So you have a medium ratio if you take in your phosphorus as dairy or even meat. And you have a very high phosphorus to good food ratio when you take plant-based proteins, chocolate or green tea, for example. Tea is a known protective food for your blood vessels.
So here is what we learned today. Phosphorus is actually a good thing. But the problem with kidney failure is that phosphorus is retained by the kidney because it’s not able to remove it. So if you eat a lot of phosphorus, then it’s going to be retained in the body. It’s going to make all kinds of changes that are bad for your blood vessels. Now, what happens is that certain phosphorus kinds are absorbed better and certain are not. And it so happens that good high-quality food also is associated with less phosphorus absorption.
So then, you need to see and talk with your dietitian to understand how much phosphorus you are able to handle in your specific situation. And then, we will need to try to take in that phosphorus with high-quality foods. And what I am not saying here is that you should always concentrate on plants alone. No, dietary preferences are very important here. But you have to have a healthy balance. And you will have to try to eliminate things that cause unnecessary phosphorus absorption. And together with phosphorus absorption, you are going to absorb things that are not going to be good for your body. Because if you don’t do that, then what you see is that your blood vessels are going to age prematurely and you will have a high risk for all kinds of cardiovascular, heart-related, blood vessel-related diseases.
So with that, I thank you for your attention and goodbye for now.
