Potassium and its role in reducing arterial blood pressure
High blood pressure is a major public health issue. There is an urgent need for population-wide strategies based on efficient diet and lifestyle approaches for preventing and treating high blood pressure in replacement or as a complement to pharmacological treatments. Increasing potassium intake by consuming a diet rich in fruits and vegetables is one of these approaches that should be promoted in developed and developing countries.
High blood pressure is a major cause of morbidity and mortality
High blood pressure (systolic pressure above 115 mm Hg and/or diastolic pressure above 75 mm Hg) is one of the leading causes of disability adjusted life years (sum of the years of life lost due to premature mortality and the years lost due to disability) in developed and developing countries(1). There is an exponential relationship between blood pressure levels and the risk of ischemic heart disease and stroke. Despite progress in prevention, detection, treatment and control of high blood pressure, much remains to be done to solve this public health issue. Until now, the medical approach has only been focused on the few individuals at high cardiovascular risk (systolic pressure above 140 mm Hg and/or diastolic pressure above 90 mm Hg), ignoring the large number of individuals at low risk (systolic pressure between 120 and 140 mm Hg and/or diastolic pressure between 75 and 90 mm Hg) although over half of the cardiovascular events related to high blood pressure occurs in low-risk individuals(2). Even in high-risk individuals, the overall control of high blood pressure remains low (only 10 % in 35-64 year old individuals) due to the insufficiencies of detection and treatment(3).
Diet and lifestyle recommendations for the prevention and treatment of high blood pressure
Current recommendations involve a population-wide strategy based on several approaches with proven efficacy for preventing blood pressure increase in low-risk individuals and for decreasing blood pressure in high-risk individuals: engage in moderate physical activity, maintain normal body weight, limit alcohol consumption, reduce sodium intake and maintain adequate intake of potassium by consuming a diet rich in fruits and vegetables(4). These approaches have additive effects on blood pressure and should be used in combination even though they are not always easy to implement for economical, political and social reasons.
Blood pressure and fruit and vegetable intake
In the 1980s, vegetarians were found to have lower blood pressure than the general population and vegetarian diets were shown to decrease blood pressure(5). More recently, transversal and prospective studies have reported an inverse relationship between blood pressure and fruit and vegetable intake(6). Clinical trials have confirmed the antihypertensive effect of a high fruit and vegetable intake per se or in the context of combined interventions(7). In parallel, several prospective studies have reported an inverse association between fruit and vegetable intake and cardiovascular risk(8).
Potassium probably explains in part the antihypertensive effect of fruits and vegetables
The hypothesis that fruits and vegetables lower blood pressure due to their high antioxidant content is supported by observational data but is not confirmed by intervention studies(9). In contrast, there is strong evidence that the high potassium content of fruits and vegetables may explain, at least in part, their antihypertensive effect. Indeed, epidemiological studies show the existence of an inverse relationship between blood pressure and potassium intake: for example in the 52 populations of the ‘Intersalt study’, the increase of systolic pressure between 25 and 55 years of age differs by 14 mm Hg when daily potassium intake differs by 1.9 g(10). Clinical trials demonstrate that increasing daily potassium intake by 2 g during a few weeks lowers systolic and diastolic pressures by 4.4 and 2.5 mm Hg(11). Increasing potassium intake also reduces the need of antihypertensive medication for controlling high blood pressure(12). Most of the trials have used potassium chloride for supplementing the diet while potassium in fruits and vegetables is mostly present as organic salts (citrate, malate). If the antihypertensive effect seems to be equivalent(13), organic salts have additional beneficial effects on calcium urinary excretion, kidney stones and bone loss due to their potential to generate bicarbonate in the organism(14).
Mechanisms of the antihypertensive effect of potassium
There is substantial evidence that potassium lowers blood pressure by causing urinary sodium and water loss in the same way as diuretics(15). This explains why the antihypertensive effect of potassium is strongly dependent on sodium intake, the effect becoming larger when sodium intake increases. Potassium has also a direct effect on the arterial wall that may intervene in blood pressure regulation and in the development of vascular disease(16).
From an evolutionary viewpoint, the human body has evolved in a potassium-rich and sodium-poor environment and is therefore adapted for secreting large amounts of potassium and retaining as much as possible sodium(17). Based on investigations in hunter-gatherer populations and in traditional rural societies, physiological daily potassium intake is probably over 10 g. In comparison, the average potassium intake in France, United-Kingdom, United-States and Italy is currently close to 3 g with a large inter-individual dispersion from less than 1 g up to 10 g per day. Thus, the vast majority of individuals in industrialized countries ingest less or much less potassium than needed(18). The general advice is therefore to increase the consumption of food items like fruits and vegetables which contribute the most to potassium intake.
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