Dietary treatment of hypertension started as early as the first decade of the 20th century. However the importance of potassium in reducing blood pressure was not considered until 1928. That was when Addison did some short-term administrations of potassium as a salt and saw a reduction in blood pressure. There were intermittent studies between then and 1983 that showed blood pressure was lowered with potassium or with certain types of diet, especially vegetarian diets. By 1983 enough physiology was understood that medical papers began to put potassium together with diet to speculate on the role of potassium in the diet.
The Vegetarian Diet And Potassium
One of the first reports to discuss potassium in the long term diet as a way to prevent hypertension was a 1983 report from Tel Aviv (1). It indicated that potassium in the vegetarian diet was responsible for lowering blood pressure.
There had been a few prior studies showing lower blood pressure in vegetarians than nonvegetarians. But those studies had been done with younger subjects on a vegetarian diet for only a short time. This study used vegetarians who averaged 19 years on a vegetarian diet. The researchers showed only 2% of vegetarians had hypertension compared to 26% in the general population.
The researchers also considered multiple factors other than the vegetarian diet that can influence blood pressure. Family history of hypertension was similar in the vegetarian and nonvegetarian groups. Because vegetarians are more health-conscious than the general population, the researchers considered smoking, coffee, alcohol, exercise and body weight. They did not feel the differences in smoking, coffee, alcohol or exercise could account for the large difference in blood pressure. The average blood pressure was 147/88 in the nonvegetarian group and 126/77 in the vegetarians.
Body weight had been shown to affect blood pressure. The vegetarians were thinner. But when the researchers matched nonvegetarians with vegetarians of the same relative weight, the vegetarians still had lower blood pressure.
Prior studies had emphasized the role of sodium in hypertension, but this study was one of the first to also understand the importance of potassium. The researchers did not do food frequency questionnaires to determine potassium in the diet. Instead they used a more accurate method of determining sodium and potassium intake.
They collected urinary potassium and sodium. They were able to show that vegetarians and nonvegetarians took in approximately the same amount of dietary sodium. But the vegetarians had a much higher intake of potassium. And the researchers showed that blood pressure went down as potassium intake went up.
Early Basic Physiology
The researchers discussed some of the basic physiologic principles then known to be responsible for potassium's effect on blood pressure. Small increases in blood potassium levels within the normal range cause long-term effects on sodium. These small increases promote sodium and water excretion in the urine, and less retention in body fluids. Increasing potassium in the diet decreases renin activity. This decreases angiotensin II (which increases blood pressure). Potassium causes blood vessels to relax, which lowers blood pressure. The blood vessel relaxation is because of the effect of potassium on the sodium potassium ATPase pump.
Many more basic physiologic effects on blood pressure from potassium and sodium have been determined since then. Knowledge of these effects provide even greater support for the importance of potassium (and especially the potassium sodium ratio) in the diet.
Other Possible Contributors To Health
Of course there are many other potential aspects about a vegetarian diet that also may contribute to health, as discussed here. A vegetarian diet includes plants that are nutrient dense. Their phytochemicals have been shown to affect cellular structure. The polyphenols in plants affect cell membrane structure, change the ion channels in the membranes, and affect cellular function.
In the vegetarian diet, the increased plant consumption contributes a much higher ratio of unsaturated fats (both polyunsaturated and monounsaturated) to saturated fats. A nonvegetarian diet that includes meat from modern animals will have a greater amount of saturated fat than a typical vegetarian diet.
Because of the emphasis that medical studies place on sodium, there has still to this day been relatively little appreciation of the importance of potassium. And there has been even less appreciation of how plants contribute to the potassium sodium ratio of the diet. The contribution of the dietary potassium sodium ratio to blood pressure is rarely considered. The importance of the ratio's effect on blood pressure and cellular balance is still not understood by many physicians and lay people.
To find tables with the potassium and sodium content of foods, click on the List of Posts tab at the top of the page.
1. Low blood pressure in vegetarians: the possible role of potassium. Ophir O, Peer G, Gilad J, Blum M, Aviram A. Am J Clin Nutr. 1983 May;37(5):755-62.