Fortnightly review: Beneficial effects of potassium

Effect of potassium salts in rats adapted to an acidogenic high-sulfur amino acid diet

Low-grade metabolic acidosis, consecutive to excessive catabolism of sulfur amino acids and a high dietary Na:K ratio, is a common feature of Western food habits. This metabolic alteration may exert various adverse physiological effects, especially on bone, muscle and kidneys. To assess the actual effects of various K salts, a model of the Westernised diet has been developed in rats: slight protein excess (20 % casein); cations provided as non-alkalinising salts; high Na:K ratio. This diet resulted in acidic urine (pH 5.5) together with a high rate of divalent cation excretion in urine, especially Mg. Compared with controls, K supplementation as KCl accentuated Ca excretion, whereas potassium bicarbonate or malate reduced Mg and Ca excretion and alkalinised urine pH (up to 8). In parallel, citraturia was strongly increased, together with 2-ketoglutarate excretion, by potassium bicarbonate or malate in the diet. Basal sulfate excretion, in the range of 1 mmol/d, was slightly enhanced in rats fed the potassium malate diet. The present model of low-grade metabolic acidosis indicates that potassium malate may be as effective as KHCO3 to counteract urine acidification, to limit divalent cation excretion and to ensure high citrate concentration in urine.

Potassium Supplementation Reduces Cardiac and Renal Hypertrophy Independent of Blood Pressure in DOCA/Salt Mice

We have demonstrated previously that deoxycorticosterone acetate (DOCA)/salt induces cardiac hypertrophy and left ventricular dysfunction independent of blood pressure (BP) in 1-renin gene mice. Because these mice also develop hypokalemia and metabolic alkalosis caused by mineralocorticoid excess, we investigated whether correcting hypokalemia by dietary potassium supplementation would prevent the DOCA/salt-induced cardiac hypertrophy, cardiac dysfunction, and electrocardiographic changes in normotensive, 1-renin gene and hypertensive, 2-renin gene mice. All mice were studied after 5 weeks of DOCA and salt administration. Potassium was given by adding 0.4 or 0.6% KCl to the drinking water. Our results show that correction of hypokalemia and metabolic alkalosis prevents cardiac hypertrophy and normalizes cardiac function without affecting BP in normotensive, 1-renin gene mice. In hypertensive, 2-renin gene mice, potassium supplementation induces a significant decrease in BP. The decrease in BP and correction of kalemia are associated with a significant but partial correction of cardiac hypertrophy. In both group of mice, electrocardiographic alterations were measured after administration of DOCA/salt, which could be corrected by potassium supplementation. Thus, these results show that correction of hypokalemia and metabolic alkalosis does prevent the development of cardiac hypertrophy and normalizes cardiac function independent of BP in normotensive, 1-renin gene mice that receive excess mineralocorticoid and salt. In 2-renin gene, hypertensive mice, potassium supplementation also prevents the development of cardiac hypertrophy, but the effect cannot be separated from the decrease in BP.

Reduction of blood pressure with calcium and potassium supplementation in children with salt sensitivity: a 2-year double-blinded placebo-controlled trial

An investigation of the reductive effect of blood pressure and increment of urinary sodium excretion with calcium and potassium supplementation in children with sodium sensitivity is conducted. In total of 261 school children who had completed a 2-year double-blinded, placebo-controlled trial with calcium and potassium supplementation salt sensitivity, with a salt volume expansion and contraction protocol, was determined. The results showed that in children with salt sensitivity, the increase in blood pressure in the supplementary group was lower by 4.3/4.8 mmHg than that in the placebo group (P<0.05), while no significant change was found between the supplementary group and placebo group in children with nonsalt sensitivity. With calcium and potassium supplementation, the night urinary sodium excretion in children with salt sensitivity was significantly increased (P<0.01), and it is negatively correlated with the increase in blood pressure. It was suggested that a moderate increase of calcium and potassium intake in children with salt sensitivity, through interaction with sodium, can promote urinary sodium excretion and may play contribute to the prevention of hypertension.

Effect of short-term supplementation of potassium chloride and potassium citrate on blood pressure in hypertensives

Randomized trials have shown that increasing potassium intake lowers blood pressure. However, most previous trials used potassium chloride, whereas potassium in fruits and vegetables is not a chloride salt. It is unclear whether a nonchloride salt of potassium has a greater or lesser effect on blood pressure compared with potassium chloride. We performed a randomized crossover trial comparing potassium chloride with potassium citrate (96 mmol/d, each for 1 week) in 14 hypertensive individuals. At baseline, blood pressure was 151+/-16/93+/-7 mm Hg with a 24-hour urinary potassium of 81+/-24 mmol. During the randomized crossover part of the study, blood pressure was 140+/-12/88+/-7 mm Hg with potassium chloride (24-hour urinary potassium: 164+/-36 mmol) and 138+/-12/88+/-6 mm Hg with potassium citrate (24-hour urinary potassium: 160+/-33 mmol). These blood pressures were significantly lower compared with that at baseline; however, there was no significant difference in blood pressure between potassium chloride and potassium citrate, mean difference (95% confidence interval): 1.6 (-2.3 to 5.6) mm Hg for systolic and 0.6 (-2.4 to 3.7) mm Hg for diastolic. Our results, in conjunction with the evidence from many previous trials that potassium chloride has a significant blood pressure-lowering effect, suggest that potassium citrate has a similar effect on blood pressure as potassium chloride. These results support other evidence for an increase in potassium intake and indicate that potassium does not need to be given in the form of chloride to lower blood pressure. Increasing the consumption of foods high in potassium is likely to have the same effect on blood pressure as potassium chloride.

Mutations in the HERG K+-ion channel: a novel link between long QT syndrome and sudden infant death syndrome

In a 7-week-old infant who experienced sudden infant death syndrome (SIDS), a novel missense mutation was identified in KCNH2, causing a lysine-to-glutamic acid amino acid substitution at position 101 (K101E). KCNH2 codes for the HERG ion channel and mutations in the gene are associated with congenital long-QT syndrome (LQTS), and in the family of this case of SIDS, the mutation was associated with Torsades de pointes tachycardia, making SIDS the most likely outcome of congenital LQTS.

Blood pressure and urinary sodium in men and women: the Norfolk Cohort of the European Prospective Investigation into Cancer (EPIC-Norfolk)

BACKGROUND

Abundant evidence indicates that a high sodium intake is causally related to high blood pressure, but debate over recommendations to reduce dietary sodium in the general population continues. A key issue is whether differences in usual sodium intake within the range feasible in free-living populations have clinical or public health relevance.

OBJECTIVE

We examined the relation between blood pressure and urinary sodium as a marker of dietary intake.

DESIGN

This was a study of 23104 community-living adults aged 45-79 y.

RESULTS

Mean systolic and diastolic blood pressure increased as the ratio of urinary sodium to creatinine increased (as estimated from a casual urine sample), with differences of 7.2 mm Hg for systolic blood pressure and 3.0 mm Hg for diastolic blood pressure (P < 0.0001) between the top and bottom quintiles. This trend was independent of age, body mass index, urinary potassium:creatinine, and smoking and was consistent by sex and history of hypertension. The prevalence of those with systolic blood pressure >/= 160 mm Hg halved from 12% in the top quintile to 6% in the bottom quintile; the odds ratio for having systolic blood pressure >/= 160 mm Hg was 2.48 (95% CI: 1.90, 3.22) for men and 2.67 (95% CI: 2.08, 3.43) for women in the top compared with the bottom quintile of urinary sodium. Estimated mean sodium intakes in the lowest and highest quintiles were approximately 80 and 220 mmol/d, respectively.

CONCLUSIONS

Within the usual range found in a free-living population, differences in urinary sodium, an indicator of dietary sodium intake, are associated with blood pressure differences of clinical and public health relevance. Our findings reinforce recommendations to lower average sodium intakes in the general population.

Protective effects of high dietary potassium: nutritional and metabolic aspects

Potassium (K+) requirements have been largely overlooked because severe deficiencies are uncommon due to the ubiquity of this element in foods. However, a transition toward modern ("Westernized") diets has led to a substantial decline of K+ intake compared with traditional food habits, and a large fraction of the population might now have suboptimal K+ intake. A high K+ intake was demonstrated to have protective effects against several pathologic states affecting the cardiovascular system, kidneys, and bones. Additionally, fruits and vegetables contain K/organic anion salts (malate, citrate), which exert alkalinizing effects, through KHCO(3)(-) generation, which serves to neutralize fixed acidity in urine. Low-grade metabolic acidosis, when not properly controlled, may exacerbate various catabolic processes (bone Ca++ mobilization, proteolysis), especially in the elderly. Fruits and vegetables are therefore receiving great attention in a strategy to increase the nutritional value of meals while reducing energy density and intake. The need to ensure a 2.5- to 3.5-g daily K+ supply from fruits and vegetables represents a strong rationale for the "5-10 servings per day" recommendations.

Sodium and potassium handling by the aldosterone-sensitive distal nephron: the pivotal role of the distal and connecting tubule

Sodium reabsorption and potassium secretion in the distal convoluted tubule and in the connecting tubule can maintain the homeostasis of the body, especially when dietary sodium intake is high and potassium intake is low. Under these conditions, a large proportion of the aldosterone-regulated sodium and potassium transport would occur in these nephron segments before the tubular fluid reaches the collecting duct. The differences between these two segments and the collecting duct would be more quantitative than qualitative. The collecting duct would come into play when the upstream segments are overloaded by a primary genetic defect that affects sodium and/or potassium transport or by a diet that is exceedingly poor in sodium and rich in potassium. It is likely that the homeostatic role of the distal convoluted and connecting tubules, which are technically difficult to study, has been underestimated, whereas the role of the more easily accessible collecting duct may have been overemphasized.

Fruit and vegetable consumption is inversely associated with blood pressure in a Mediterranean population with a high vegetable-fat intake: the Seguimiento Universidad de Navarra (SUN) Study

There is evidence that a diet rich in fruit and vegetables reduces blood pressure (BP). Characteristically, the Mediterranean diet is rich in plant-derived foods and also in fat, but studies conducted in Mediterranean countries to relate diet to BP are scarce. We studied the association between fruit and vegetable consumption and BP in a cross-sectional analysis of 4393 participants in the Seguimiento Universidad de Navarra (SUN) Study, an ongoing dynamic cohort study in Spain. Diet was measured using a food-frequency questionnaire previously validated in Spain. Fat represented more than 37 % total energy intake. Subjects were considered to have undiagnosed hypertension if they reported systolic BP > or = 140 mmHg or diastolic BP > or = 90 mmHg, and not a medical diagnosis of hypertension. The adjusted prevalence odds ratio of undiagnosed hypertension (upper v. lowest quintile) was 0.58 (95 % CI 0.36, 0.91; P for trend 0.01) for vegetable consumption and 0.68 (95 % CI 0.43, 1.09; P for trend 0.10) for fruit consumption. Comparing those in the highest quintile of both fruit and vegetable consumption with those in the lowest quintile of both food groups, the prevalence odds ratio was 0.23 (95 % CI 0.10, 0.55; P = 0.001), after adjusting for risk factors for hypertension and other dietary exposures. In a Mediterranean population with an elevated fat consumption, a high fruit and vegetable intake is inversely associated with BP levels.

The 45-year story of the development of an anti-aldosterone more specific than spironolactone

At the early stage of its development in 1957, the daily dose of spironolactone necessary to improve various pathological conditions was not precisely determined and dose-dependent sexual side effects limited its long-term use. Prescription of high daily doses and absence of selectivity for the mineralocorticoid receptor explain these limitations. The 9-11alpha epoxy group added to mexrenone by the Ciba-Geigy chemists in 1984 and improved chemical synthesis at Searle, permitted the original international clinical development of a selective antagonist for high blood pressure and congestive heart failure treatment. This review deals with the main methodological issues of a 20-year biological and clinical development of eplerenone, the second antimineralocorticoid drug. The investigation of a large range of daily doses (25-400mg) initially selected in normal volunteers by the 9alpha-fluorohydrocortisone test has led to the conclusion that 50-100mg q.i.d. doses of eplerenone offer a favorable benefit/risk ratio in various patient populations by neutralization of the aldosterone effects on blood pressure and target organ damage. The absence of sexual side-effects has confirmed the clinical relevance of the initial biological hypothesis on the need for more selectivity at the androgen and progestogen receptor sites. Widening the distance between efficacy and adverse effects of an anti-mineralocorticoid drug will facilitate the long-term maintenance of a moderately negative sodium balance and a slightly positive potassium balance, while minimizing the direct effects of salt and aldosterone on the heart, vessels, brain, and kidneys. Wide use in unselected patients and additional controlled clinical trials are necessary to confirm the benefits expected from animal and clinical research given that a 45-year interval also characterizes the story of the Na-Cl cotransporter (NCC) blocker, chlorthalidone, from its initial clinical use to the demonstration of its beneficial effects on cardiovascular morbidity and mortality.

Vegetable and Fruit Intake and Stroke Mortality in the Hiroshima/Nagasaki Life Span Study

BACKGROUND AND PURPOSE

Fruits and vegetables are known for their beneficial effects on chronic diseases. The purpose of the present study was to investigate the protective effect of a diet rich in fruits and vegetables on total stroke mortality and its 2 main subtypes in men and women separately.

METHODS

A prospective cohort study of 40 349 Japanese men and women was initiated in 1980-1981 and followed until 1998. Fruit and vegetable intake was assessed at baseline on the basis of the response to a food frequency questionnaire. During the 18-year follow-up period, deaths from stroke were registered.

RESULTS

A total of 1926 stroke deaths were identified during the follow-up period. An increasing frequency of intake of green-yellow vegetables and fruit was associated with a reduced risk of death from intracerebral hemorrhage and cerebral infarction. Daily intake of green-yellow vegetables was associated with a significant 26% reduction in the risk of death from total stroke in men and women compared with an intake of once or less per week. The protective effect associated with daily fruit and vegetable intake was observed for both cerebral infarction and intracerebral hemorrhage mortality but was slightly stronger and clearer for infarction than for hemorrhage, with a 32% reduction in men and a 30% reduction in women. Daily fruit intake was associated with a significant 35% reduction in risk of total stroke in men and a 25% reduction in women and was equally strong for both intracerebral hemorrhage and cerebral infarction.

CONCLUSIONS

Daily consumption of green-yellow vegetables and fruits is associated with a lower risk of total stroke, intracerebral hemorrhage, and cerebral infarction mortality. The protective effects are similar in both men and women.

Dietary minerals and modification of cardiovascular risk factors

High serum cholesterol, hypertension and obesity are major risk factors for cardiovascular diseases, and together with insulin resistance form a deadly disorder referred to as the metabolic syndrome. All the aspects of this syndrome are strongly related to dietary and lifestyle factors; therefore, it would be reasonable to look for dietary approaches to their modification. Mineral nutrients, such as calcium, potassium and magnesium, lower blood pressure, and especially calcium has beneficial effects also on serum lipids. Recent evidence suggests that increased intake of calcium may help in weight control as well. This review summarizes previous literature on the effects and use of dietary minerals on serum lipids, blood pressure and obesity, with specific focus on the effects of calcium. Calcium and magnesium as divalent cations can form insoluble soaps with fatty acids in the intestine and thus prevent the absorption of part of the dietary fat. Decreased absorption of saturated fat leads to reduction in serum cholesterol level via decreased production of VLDL and increased intake of LDL in the liver. Dietary calcium may also bind bile acids, which increases the conversion of cholesterol to bile acids in the liver. Furthermore, calcium appears to enhance the cholesterol-lowering effect of plant sterols. Thus, dietary combination of the mineral nutrients and plant sterols provides a promising novel approach to the modification of cardiovascular risk factors.

Low intake of fruits, berries and vegetables is associated with excess mortality in men: the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study

Diets rich in fruits and vegetables have been of interest because of their potential health benefits against chronic diseases such as cardiovascular disease (CVD) and cancer. The aim of this work was to assess the association of the dietary intake of a food group that includes fruits, berries and vegetables with all-cause, CVD-related and non-CVD-related mortality. The subjects were Finnish men aged 42-60 y examined in 1984-1989 in the prospective Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study. Dietary intakes were assessed by 4-d food intake record during the baseline phase of the KIHD Study. The risk of all-cause and non-CVD-related deaths was studied in 2641 men and the risk of CVD-related death in 1950 men who had no history of CVD at baseline. During a mean follow-up time of 12.8 y, cardiovascular as well as noncardiovascular and all-cause mortality were lower among men with the highest consumption of fruits, berries and vegetables. After adjustment for the major CVD risk factors, the relative risk for men in the highest fifth of fruit, berry and vegetable intake for all-cause death, CVD-related and non-CVD-related death was 0.66 [95% confidence interval (CI) 0.50-0.88], 0.59 (0.33-1.06), and 0.68 (0.46-1.00), respectively, compared with men in the lowest fifth. These data show that a high fruit, berry and vegetable intake is associated with reduced risk of mortality in middle-aged Finnish men. Consequently, the findings of this work indicate that diets that are rich in plant-derived foods can promote longevity.

The potential benefits of aldosterone antagonism in Type 2 diabetes mellitus

Interest in the renin-angiotensin-aldosterone system (RAAS) has increased since the development of angiotensin-converting enzyme (ACE) inhibitors. It has been discovered that the potential uses of this class of treatment extend far beyond their initial developmental role as antihypertensives, and they are now used routinely in the treatment of heart failure, nephropathy, myocardial infarction and diabetes. However, there is more to RAAS blockade than just inhibition of angiotensin II, and inhibition of aldosterone is becoming recognised as an additional therapeutic manoeuvre in chronic heart failure. Since inhibition of the RAAS at the level of ACE is now seen to be an important therapy in diabetes; the purpose of this article is to explore the potential benefits of additional aldosterone inhibition in Type 2 diabetes mellitus.

Importance of potassium in cardiovascular disease

The pivotal role of potassium (K+) in cardiovascular disease and the importance of preserving potassium balance have become clinical hot points, particularly as relates to new and emerging cardioprotective and renoprotective therapies that promote potassium retention. Although clinicians may be aware of the critical nature of this relationship, quite frequently there is some uncertainty as to the best way to monitor potassium levels in the face of a host of pathologic states and/or accompanying drug therapies that affect serum levels and/or total body potassium balance. Moreover, guidelines for monitoring of serum potassium levels are at best tentative and oftentimes are translated according to the level of concern of the respective physician. To address these uncertainties, an expert group was convened that included representatives from multiple disciplines. They attempted to reach consensus on the importance of K+ in hypertension, stroke, and arrhythmias as well as practical issues on maintaining K+ balance and avoiding K+ depletion. Because of the complexity of this topic, issues of hyperkalemia will be addressed in a forthcoming manuscript.