Sodium and potassium have opposite effects on blood pressure. The balance between them determines many bodily processes. Blood pressure's relation to sodium and potassium is one of the most studied of the processes. There are many epidemiological, experimental, and clinical studies that show an association of blood pressure with total body sodium and an inverse association with total body potassium. Because of this apparently opposite effect of sodium and potassium, a dependent duality, the authors of the publication (1) to be discussed today consider it the yin and the yang of blood pressure regulation. Although they only touch on the basic science aspect of potassium and sodium balance, they cover many of the clinical studies associating low potassium intake with high blood pressure and resulting diseases.
Basic Cell Physiology
One of the basic principles in cellular physiology is that for each potassium exiting a cell, a sodium will replace it. There are many passive channels in the cell membrane to assure that this will happen. And there are active pumps, such as sodium-potassium ATPase, to restore a proper balance of sodium and potassium inside and outside of the cell. Much of our daily energy consumption goes to maintaining this balance because of its great importance.
As the authors discuss, 1/4 of the adult world population has hypertension and the percentage is increasing. Hypertension is preventable for the great majority of people. Blood pressure is dependent upon multiple genes, but the expression of those genes is dependent upon the environment of those genes. The environment of the genes is largely determined by the environment of the cell. And the environment of the cell is largely determined by what is eaten. For blood pressure, sodium and potassium are the most important factors of what is eaten.
The authors' paper discussed how potassium affects hypertension and cardiovascular disease if there is normal kidney function. They discussed epidemiological and clinical trials that associate potassium intake inversely with blood pressure, and various cardiovascular and other vascular diseases.
The Clinical Studies
The first trial the authors discussed was the Intersalt trial. This trial showed that the potassium urinary excretion rate was inversely related to blood pressure in a large, diverse group of populations. It then discussed two studies of a low potassium diet in hypertensive and normotensive patients with normal kidney function. These studies showed that a low potassium diet led to an increase in systolic and diastolic pressures. Another study by one of these investigators also showed that a very low potassium diet in normotensive healthy males led to a large increase in blood pressure.
The randomized controlled study the authors discussed used a high potassium diet of natural foods. When it was given to hypertensives who were on medications with normal kidney function, it led to a decrease in the medications. 81% of those on the high potassium diet had a reduction in their medications. Only 29% of those on a low potassium diet reduced their medications.
The authors also discussed the DASH diet study that included a high intake of potassium in the diet. This was a randomized controlled trial that lasted 8 weeks. It used people whose systolic blood pressure was less than 160 and whose diastolic ranged between 80 and 95. The diet was a high potassium, low sodium and low fat diet. The results were that the hypertensives reduced their blood pressure by 11.4 systolic, and 5.5 diastolic. The normotensive subjects reduced their blood pressure by 3.5 and 2.1, systolic and diastolic respectively.
A later DASH diet study used 3 levels of sodium intake. The group with the lowest level of intake had the least reduction in blood pressure. But because of the complexity of the changes in diet, it is difficult to draw conclusions. Other dietary factors may have been involved in the blood pressure changes, such as antioxidant content, fiber or fats.
The authors then discussed epidemiological and clinical trials in which there was an association of potassium intake and cardiovascular outcomes. There were 2 studies concerning stroke, and 3 studies concerning cardiovascular disease, that the authors discussed.
In the 2 studies concerning stroke, the researchers showed that when the potassium intake was increased by only 390 mg per day there was a 40% reduction in stroke related deaths. The second study that the authors discussed was a meta-analysis of prospective studies of strokes. This study found that 1640 mg of potassium daily reduced strokes by 21%.
In the studies concerning cardiovascular disease the authors discuss the Interheart study and the NHANES III study. The Interheart study placed subjects on a higher fruit and vegetable diet, and compared them to a control group on a normal diet. They found that there was a 30% reduction in myocardial infarctions.
In the NHANES III study a look at the potassium sodium ratio showed that the higher the ratio, the less the mortality from ischemic heart disease, cardiovascular disease and all causes.
The authors also discussed the Taiwanese study of elderly veterans in a retirement home. The dietary change in potassium and sodium in this study could be accurately determined because the setting was highly controlled. A discussion of that study can be found at the post we made here.
Basic Science Studies
The authors also discuss the mechanism of potassium's effects on blood pressure and on end-organs. They focus on the kidney effect and the blood vessel effect. In most of our posts on this website we have emphasized how the potassium sodium ratio affects all cells, and have especially discussed the kidney and heart cells. We have emphasized the cellular molecular effects. The authors in this article discussed mostly the effect of the ratio at the organ level.
In the discussion of potassium's effect on the kidney, they point out how reducing potassium leads to sodium retention. When there is an increase in potassium consumption, there is an increase in potassium and sodium excretion in both hypertensives and normal subjects. We have discussed the mechanism of how the kidney does this in this post found here.
They also discussed how increasing potassium modulates blood vessel sensitivity to catecholamines, such as epinephrine and norepinephrine involved in the “fight or flight” response. When there is less sodium in the body, there is less increase in blood pressure when norepinephrine is given. In the particular study that this was shown, the subjects were also given a high potassium intake. The researchers found that the diastolic blood pressure dropped by 5 mm Hg in half of the subjects with the higher potassium intake.
The authors also discussed the effect of potassium on the cells that line blood vessels. They cited studies that show that potassium counters some of the effects of sodium that lead to stiffness of the blood vessels. Because there are not many basic science studies specifically of the effect of the interaction of these two ions in the blood vessel lining cells, the authors were limited in their discussion. But there are many studies showing the effect of potassium alone. And even more studies showing the effect of sodium alone on specific cells.
Overall this was a good, brief summary of many of the medical epidemiological and clinical trials. These trials are confirmed by many basic science studies, some of which have been discussed on this website.
1. Dietary potassium: a key mediator of the cardiovascular response to dietary sodium chloride. Kanbay M, Bayram Y, Solak Y, Sanders PW. J Am Soc Hypertens. 2013 Sep-Oct;7(5):395-400. doi: 10.1016/j.jash.2013.04.009. Epub 2013 Jun 2.