Many people believe that the more water you drink, the better it is for your kidneys. In this post, I explain why this idea can be misleading and why it’s not the absolute amount of water that matters most, but the balance between salt and water. We discuss when too much fluid can be harmful, when too little becomes dangerous, what symptoms point to these states, and why fluid intake, diuretics, and blood pressure medications need to be handled with particular care in people with kidney or heart disease. Here, too, the emphasis is on balance and individualized interpretation rather than one-size-fits-all advice.
The content of the video in written form
Hello, this is Dr. Zsom. Dear patience!
Well, our physiologist colleagues, great scientists, tell us that most of the human organism consists of water. More than 90 percent of the composition of the human organism is water. Well, if we think about water like this, this is a glass of water, then we are gravely mistaken. And our physiologist colleagues don’t even realize that they misled us. And the problem is that it’s not only the patients, but also medical students and dietitians are the ones that get misled quite a bit.
Well, if we make an experiment, and let’s make this experiment as a thought experiment, and we would give water through it as a fluid replenishment, we give water to somebody who just ran the marathon. What would happen? Well, that poor runner would probably die. Why is that? Because it’s not water that that person needs. This is salt. This is a solution of salt in water. This is sugar. This is a solution of salt and sugar in water.
So we will see that in the blood, in the kidney, and in the cells in general, it’s not water that is there, but it’s a solution of many different things. And among them, one of the most important solvents, in other words a substance that is solved in water, is salt. That’s sodium chloride. So it’s very very important to realize that, because if we believe that the fluid that we need to replace is plain water, and if we drink water, then we are not going to do much when we need fluid replenishment.
So there are all kinds of misconceptions, like for example we need to kind of flush the kidneys, wash them through with water, and then the kidneys will work better. Well, kidney function has nothing to do with water intake. On the contrary, what we need to wash through the kidneys is a good circulation, and in certain instances fluid intake can decrease circulation. We will talk about that in detail. So drink a lot of fluids to improve your kidney function, that’s what they tell you, but this is simply either not true or the very opposite of this might be true. So lots of water indeed dilutes urine, but what does it do to the kidney function? Or let’s rephrase that by saying, is it really good to overfill a tub? So if it’s already almost full, does it really make sense to fill it even more?
Well, let’s think about a bathtub. So there is this drain here, and that drain has a certain capacity. So if you then put a lot of fluid in this tub, then you might overwhelm the capacity of that drain, and then it will overflow, right? So the heart is as much a pump as the kidney a filter. It is an oversimplification, yet we need some oversimplifications to begin to understand something. So even a pump, a simple pump, has an ideal range of pressure in which it can optimally operate. So if there is too much fluid, in this case salt and water, that can constitute a resistance against this pump. So the pump is not going to work well. Or if there’s too little salt and water, that means that there is not enough filling pressure, so that once again the pump is not going to operate optimally.
So that means that there is an optimum amount of salt and water that you have to eat and drink so that the pump works better, and depending on the circumstances, this optimum changes day by day. So once again, fluid always means salt and water, because water in itself does nothing to the heart and does nothing to the kidney.
So the kidney usually is able to compensate, so far as the kidney is healthy. The kidney is there, among other things, to regulate the fluid status in the body, and that means it regulates the total amount of salt and water in the body and their ratio. So salt to water ratio, otherwise known as sodium concentration in the blood, it’s closely regulated by the kidney. The problem is that if you eat and drink too much salt and water, in a risk your fluid intake is very high chronically, then as we said here, the drain is overwhelmed, the pump is overwhelmed, and what you have is heart and kidney failure. And heart failure makes kidney failure worse, kidney failure makes the heart failure worse, and hypervolemia, meaning too much salt and water, makes both worse.
Kidneys love oxygen. So that means that one of the most important goals is to maintain a good circulation to the kidney. So maintain an optimal blood flow. One of the things that you need to do is to make sure that your heart is working optimally, so that it can pump enough blood, and with that it can give enough oxygen to the kidneys. If you have excessive salt and water, it may damage both blood vessels and the heart, and so your heart function is going to be worse and worse on the long run. So it will decrease, and therefore the kidneys don’t get enough oxygen.
Resource for testing if too much salt and water is causing blood vessel damage and high blood pressure, and these left their mark on the kidney, is proteinuria. Proteinuria can also be caused by certain special kidney diseases, but by and large, proteinuria is a pretty good measure of how much too much salt and water, too much blood pressure, causes the kidney to remove protein, which is to filter protein, which it’s not supposed to do because it’s supposed to retain protein. So the more the protein in the urine, the more either your blood pressure or your pressure inside the little kidney arteries is too high, and one of the reasons for that could be too much salt and water in the body. So the more the protein or the more the kidney damage from blood vessel damage, both sign and treatment target. In other words, there are certain medications, kidney protective agents and others, to decrease proteinuria, and that’s an important target for us. But obviously diet is also very important, because just like I said, too much salt and water can cause proteinuria to get much worse.
So the absolute amount and the ratio of salt and water is closely regulated by the kidneys, except when chronic kidney disease is already present, and that means that the fluid is retained, and that further damages the blood vessels in general and in the heart and kidney in particular. So this fluid retention is a progressive risk that manifests differently in different individuals with different lifestyle and diet. So if somebody tends to eat a little too much pizza, then that means that if the kidney starts to fail, there’s less and less and less compensation, and that person will have much faster progression of heart and kidney disease. So there is always an optimum of fluid intake that must be individually tailored for a given patient. Obviously it’s different if you walk in the desert or if you just sit at home comfortably.
So this is the case of the empty bathtub. You may have diarrhea, vomiting, fever, profuse sweating, for example because you are touring here in the desert, walking a lot, there’s lots of appetite. This is the time to push fluids, but fluids here means salt and water. So when we give IVs, they also contain salt and water. The water in itself is not going to be sufficient. Remember poor marathon runner? So it’s a life and kidney saver to push fluids in those situations. This is the time to hold diuretics, because obviously it doesn’t make sense to make the kidneys lose even more salt and water when salt and water is already in a deficit. And certain blood pressure medicines may need to be held because the blood pressure may be low, especially the kidney protecting ones, because they decrease the pressure inside the small kidney arteries, so that they are especially harmful in this kind of situation.
So if your bathtub is full, then reduce your fluid intake, ask your nephrologist how to increase diuretics. Remember, fluid equals salt and water, so reducing fluid intake also means reducing salt intake. The example of the esophageal fungal infection: I had a poor patient who had a kidney transplantation, was on powerful immunosuppressive medications, developed a fungal infection of the esophagus, and all of a sudden we saw that his advanced heart failure begins to improve. Why? Because the heart failure was caused by too much salt and water, and when he was unable to eat too much salt and water, then the heart was all of a sudden improving. So there was less burden on it by excessive salt and water.
In chronic kidney disease, the ability of the kidneys to regulate sodium and water ratio, the concentration, is imperfect. So in average, the kidney cannot regulate as well as if it was healthy. So a low sodium concentration in the blood in this particular situation often signals an abnormal ratio of sodium to water. So that means that you do not have a sodium deficit, but you, compared to the excessive amount of water, you have less of an excessive amount of sodium. In this situation, you have to remove both sodium and water, and diuretics remove excess salt and water through the kidneys, even in chronic kidney disease. So diuretics is a good idea in this situation, and you do not need to replenish your sodium because there is no sodium deficit. It’s just simply too much water and too much sodium, but more water than sodium.
So therefore it is counterproductive to drink a lot of water or eat a lot of salt with diuretics. On the contrary, the more the fluid intake, the more diuretics are needed. So if you don’t want to take that much medications, then stop drinking too much water and stop eating too much salt, and then you can reduce your diuretics. So when the bathtub is full, the kidney and hearts suffer. If diuretics are started, do not replenish the fluid loss. A negative fluid balance is a key. Obviously it has to be a slightly negative fluid balance, otherwise your blood pressure is going to drop. So either lots of fluid and lots of diuretics, or less fluid and less diuretics. Fluid intake and losses change day to day. Diet, sweating, diarrhea make it essential to adjust diuretics dosages accordingly. Salt means thirst means water intake. So if you eat too much salt, then it’s automatic that you are gonna also drink a lot of water, and we use water intake as a marker of how much salt you eat, except if your blood sugar is high, it can cause the same effect. So in other words, what that means is that a lot of salt automatically means that your fluid status is going to be high.
Several scientific papers over many decades consistently prove that pushing water in itself does nothing to the filtering capacity of the kidneys or even blood pressure. So that there is no reason to drink too much water, except if because of a special condition you have too little water in your body. In that case, you need both salt and water to replenish that. So the ancient Greeks have this little phrase, mēdén ágan, which means nothing in excess. So in general, what you want to do is the middle of the road, the golden mean. Not too much, not too little. Not too much salt, not too much water. Not too little salt and not too little water. Just in the middle.
So what happens if you have too much fluid in your body? Then you can have leg swelling, high blood pressure, you have difficulty climbing stairs or in general just exercise. You may have shortness of breath even at rest. Your neck veins are going to be filled up, and your abdomen is going to be filled up with water. It’s in a situation like this, it’s important to get rid of water with diuretics and less salt and water intake. But it’s important to know that there are some rarer conditions that can also give you these signs. If you have right side heart failure from heart valve problems, lung or lung circulation problems, advanced heart failure, or sleep apnea, then you may have these symptoms even if you do not have too much water and salt in your body. But by and large, it’s really the most common cause of these symptoms is that you have too much salt and water.
Another interesting scenario is if you have kidney disease, liver disease, or cancer, you may have too low protein in your blood, and that might cause these problems. So to sort all of this out, you always have to consult your nephrologist.
So the signs of hypovolemia is poor skin turgor. Your skin is like that, kind of wrinkly. Low blood pressure, nausea, vomiting, dry tongue, and dizziness. Now it’s important to realize that too many blood pressure medications, heat wave, anemia, infections, and disorders of the autonomic nervous systems such as in diabetes can cause some of these symptoms also. But very often when you have these symptoms, that means that the fluid status is too low for you, and you have to replenish it. But you also have to decrease your medications which may aggravate the problem.
So fluid status works both ways. Too low is a problem and too high is a problem. If you have too low fluids, you have reduced blood supply to the kidney, aggravated by hardening of the arteries, blood pressure lowering medications, kidney protective medications, diuretics, and nonsteroidal anti-inflammatory drugs, in other words the drugs that you use for aches and pains. So it’s important that you avoid too low fluids, which means water and salt too low in your body. You don’t eat well because of an acute illness, for example. So that’s a problem. But too high is also a problem, because your capillaries, the small blood vessels inside the tissues, will get compressed by too much salt and water, which causes swelling in the tissues. Your circulation is compromised in all tissues, including the kidneys. The heart is overburdened. There is heart failure. There is bowel edema causing inflammation on the blood vessels and high blood pressure. So too low is a problem, too high is a problem.
So there is yet another special circumstance when you are on dialysis or you receive all of a sudden too much diuretics, especially if you have an infection or heart failure or diabetes with too much sugar. Then what can happen is that even though you have too much fluid, all of a sudden you drop your blood pressure and you feel terrible. This can happen, for example, when you have heart failure. You eat too much, and on dialysis, in just a few hours we try to remove all the fluids that would be necessary to remove. So what happens is that we remove salt and water from the blood only, and it needs to be refilled from the tissues. So this refill has, you know, a certain maximum capacity. If you go above and over that, then obviously you are going to have a decreased amount of salt and water, and you drop your blood pressure, and that can be very very inconvenient. So you develop all kinds of symptoms. So it’s very important that we don’t remove fluid all of a sudden. So if you bring in less fluid, then you have less of a chance that we will remove too much fluid in a short amount of time, either by a dialysis machine or diuretics, and so you avoid this kind of problems. So again, just middle of the road. Not too much fluid, not too little fluid, just a moderate amount.
So how do we put all of this together? Maintaining fluid status is one of the core functions of the kidney, largely independent of filtering function. But yet, if you have chronic kidney disease, maintaining fluid status will be more and more difficult for the kidneys, so that you have to be sure that your fluid intake and food intake needs to be stable and moderate. Kidney or cardiovascular disease decreases the adaptability of the kidney, and so therefore you need to help your kidneys. Blood pressure medications, kidney protective agents, diuretics, and nonsteroidal anti-inflammatory drugs make this even more difficult, because they tend to decrease the circulation inside the kidney. If you, in addition to this, have another disease, for example diarrhea or an acute infection, infections, anemia, heart failure, especially right side heart failure as in chronic lung diseases, make this worse.
So kidney disease means diet. Eat less salt and less water, except if you need it, because of heat, diarrhea, and infections. So basically, because the adaptability of your kidneys, the kidneys are reduced, you need to help them. Not too much salt, not too much water. If everything is stable, pushing fluids is unnecessary and may be harmful, because if you drink too much fluid and if your kidney is unable to adapt, then you can develop heart and kidney failure, and from that bowel edema causing inflammation on the blood vessels, which make all of these things worse. And so diuretics and blood pressure medication should be adjusted to diet and should be adjusted to acute disease, be it an infection or diarrhea or whatnot. It needs to be even adjusted to heat wave, for example. So all of these things need to be reassessed frequently and are best done by a nephrologist.
So bring your medication list. Let’s review the medication changes. Let’s look at your blood pressure diary, and let’s readjust your medications. So you need to keep in contact with your nephrologist, and then what happened, tell them what your current situation is, and all of this will be then discussed accordingly.
And with that, I thank you for your attention and goodbye for now.
