while when reading advice for reducing blood pressure, sometimes drinking water(H2O) is recommended. However, authority websites including the National Heart, Lung and Blood Institute and the Mayo Clinic do not mention drinking water(H2O) to decrease blood pressure, when discussing treatments and social lifestyle changes.

Then Why should some articles say that drinking water(H2O) lowers blood pressure?

Role of water in High blood pressure.

The basic idea that drinking water(H2O) will lower blood pressure seems to come from the idea that when water(H2O) is taken in large quantity, that sodium(Na) which is responsible for retaining water(H2O) inside the body, will be flushed out of the body and as a result pressure will drop.

After all, several classes of diuretics are very effective at reducing blood pressure like thiazide diuretics. These diuretics function by increasing the loss of sodium(Na) from the body and an increased volume of urine. Both the loss of sodium(Na) from the blood and decreasing the blood volume result in decreased high blood pressure. So, if medicine, that effectively lower blood pressure in most people, work by increasing the volume of urine and the amount of sodium(Na) in the urine, then drinking more water(H2O) should do the same thing?

Unfortunately, there is a problem with this idea. To understand why, it is necessary to understand that the body very tightly controls the levels of fluid and ions such as sodium(Na) and calcium. For optimal functioning, the body has evolved a wide range of control processes that are involved in keeping many ions and fluid levels within a narrow range.

Diuretics act on parts of the nephron system in kidney that control sodium(Na). For instance thiazide diuretics bind to, and inhibit, a protein called the Na/Cl symporter (Na=sodium(Na), Cl=chloride) that controls the amount of sodium(Na) that is reabsorbed back into the blood from the urine that is being formed. The result is that the body recovers less sodium(Na) from the urine as it is being formed, and so more sodium(Na) is lost along with more water(H2O) in urine. So diuretics affect the regulatory system and change a part of this.

so it will not change the total amount of sodium(Na) in the urine, or change the blood volume. Drinking more water(H2O) will increase the volume of urine as the body regulates fluid levels, to keep the blood volume stable. Additionally, the same amount of sodium(Na) (and other ions etc.) in a bigger volume will increase volume of urine.

Think about the color of urine. If not much fluid has been consumed, or there has been a lot of sweating, there will a small quantity of urine with a strong turbid yellow color (from urobilin). If a person is well hydrated, there is more urine with a pale or white color. Same thing with sodium(Na), In a healthy individual, the greater the volume of urine due to increased fluid intake, the lower the concentration of sodium(Na).

So the bottom line is that, generally, increasing the amount of water(H2O) that is consumed will not increase the amount of sodium(Na) lost by the blood, so blood pressure will not be decreased.

In fact, drinking water(H2O) can actually cause a very short term increase in blood pressure in some people, particularly those with some types of very low blood pressure. This is only temporary and has no long term impact on blood pressure. This is very similar to a pipe, and we close its one end, and add more and more water from other side of pipe, then pressure inside the pipe will be increased. Similar is the case with blood pressure vessels.

So the idea is, Keeping hydrated is good for health, but overhydration has no benefit for lowering your blood pressure (Hypertension).

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