Potassium supplements and bioavailability: what are we missing in treating hyperkalemia?

Potassium Supplements and Biological Availability: What Are We Missing When Treating Hyperkalemia?

Richard Kundelis Lithuanian University of Health Sciences

Introduction

Hyperkalemia, a metabolic disorder characterized by altered potassium excretion through the urinary and digestive systems and metabolic acidosis, frequently occurs in chronic kidney disease (CKD) patients [1]. Strikingly, hyperkalemia prevalence in CKD patients can hit 14-20% [2]. This condition has links to worse clinical outcomes. A very high potassium concentration in the blood serum can trigger off life-threatening rhythm disturbances. Even moderately elevated potassium levels in the blood serum can drive up the risk of mortality for future patients [1].

Physicians dietitians often adjust the diet of CKD patients to prevent hyperkalemia [1]. Using two main strategies, they reduce dietary potassium intake and apply pharmacological treatment to increase potassium excretion through urine and feces [1]. This not only effectively decreases the potassium intake, but it also ensures the patients meet their nutritional needs [3]. Because many CKD patients follow highly restrictive diets, professionals often modify these patients' diets to correct protein, phosphorus, and sodium concentrations [3, 4].

This article briefly reviews the dietary recommendations applicable to CKD patients, current evidence on the biological availability of potassium in fruits and vegetables, discusses the impact of potassium supplements on health, making the selection of suitable products even more challenging.

Recommendations Do Not Consider Potassium Biological Availability

In the 2010 nutrition and dietetics academy guidelines for CKD, patients with stage 3-5 CKD who develop hyperkalemia are recommended to limit dietary potassium intake to 2.4 g/day. [5]. Similar information is provided in the recommendations prepared by the National Kidney Foundation Dialysis Outcomes Quality Initiative group: potassium intake for the same patient population should be less than 2-4 g/day. [6]. On the other hand, there have been some changes in the CARI (Caring for Australasians with Renal Impairment) guidelines: in 2005, specialists recommended limiting potassium intake to 3,120 mg/day when serum concentration exceeds 5.5 mmol/l, but in the 2013 update, these conditions were no longer present - all patients with hyperkalemia, after consulting with a physician dietitian, must reduce potassium intake [7, 8]. One of the universally available sources of information on a low-potassium diet is the National Kidney Foundation website, which categorizes food products into groups (e.g., fruits, vegetables) containing high amounts of potassium (more than 200 mg per serving) [9]. The only drawback is the lack of specific recommendations related to artificial potassium supplements. In the 2005 version of the CARI recommendations, food products containing high, moderate, and low amounts of potassium were classified into similar groups: fruits, vegetables, grains, beverages, and others (including products such as potato chips or tomato paste) [7]. Unfortunately, potassium supplements are not discussed in this publication. When it comes to phosphorus-related guidelines, the situation is different. One example is the 2017 KDIGO (Kidney Disease Improving Global Outcomes) recommendations, which include a section considering all possible sources of phosphorus in food products; this is done to ensure effective dietary correction. National Kidney Foundation informational sources for patients separately discuss phosphorus supplements [11]. The main reason for interest in phosphorus is the improved understanding of the differences in the biological availability of phosphorus found in various food products: the least of this chemical element is absorbed from plant-based products - 40%, animal-based - 60-80%, mostly - from supplements (100%). Specialists who have identified these factors claim that additives in processed food products can increase phosphorus intake up to 700-800 mg/day. [12]. Although there is no similar literature on potassium biological availability, the available data suggest that the situation may be similar [13-15].

Potassium and Plant-Based Products

There are quite a few differences between plant and animal cells. Perhaps the most important and well-known difference is that plant cells have a cell wall, which is not characteristic of animal cells. Naismith and colleagues posit that the cell structure of plants significantly reduces the biological availability of potassium in fruits and vegetables [13, 15]. Because plant-based potassium is essentially a chemical element inside cells and digesting the cell wall is quite challenging, most of this potassium gets eliminated through the digestive tract. In individuals whose bodies effectively regulate normal blood serum potassium concentrations, the body expels almost all dietary potassium in the urine. Thus, measuring urine potassium concentrations serves as a reliable method for assessing dietary potassium intake [13]. The same team of scientists later evaluated this claim by conducting a study wherein they applied two different diets. The first group's diet consisted of a large amount of animal proteins and processed plant products (juices), while the second group's diet included fruits and vegetables. The total potassium intake was respectively 3,533 mg/d and 4,194 mg/d. After a 24-hour urine test, it was found that the participants in the first (high bioavailability) group excreted 3,392 mg of potassium in their urine (141 mg less than consumed), while the second group excreted only 3,220 mg (973 mg less than consumed). Based on these results, Naismith's group of scientists concluded that the biological availability of potassium when consuming unprocessed plant-based products is up to 60%. Similar results were obtained in the DASH (Dietary Approaches to Stop Hypertension) study in both the general and LIL patient populations. In the same study, a team of scientists applied 1 of 3 diets to 459 individuals with elevated blood pressure for 11 weeks. The research team assigned the first group a standard North American diet containing 1,700 mg of potassium. They gave the other 2 groups diets with a much higher potassium content (4,700 mg) with slight differences: one group ate a diet of fruits and vegetables, while the other included whole grains, nuts, seeds, and low-fat dairy products in addition to fruits and vegetables. This second group followed what is often referred to as the DASH diet, effective in reducing blood pressure in individuals with arterial hypertension and stage 1 LIL. After conducting a 24-hour urine test, researchers found that patients on the standard North American diet excreted about 90% of the potassium they consumed. In contrast, those on the second and third diets excreted only up to 60%. In both cases, the body did not absorb approximately 2 g of potassium. From these data, a conclusion can be drawn that fruits and vegetables offer only around 50% biological availability of potassium.

 Tyson and his team also observed the effect of the DASH diet on 11 patients with aGFG ranging from 42 to 62 ml/min./1.73 m2. In this controlled diet study, patients were assigned 2 different diets over 3 weeks: the first week - a control diet containing 1,700 mg of potassium, and the second and third weeks - the DASH diet. The results did not differ from existing trends: by increasing the potassium intake to 3,000 mg, only 780 mg more potassium was excreted in the urine. This information can also be useful in practice. Regardless of the current diet, increasing the intake of fruits and vegetables can positively adjust indicators showing kidney damage and metabolic acidosis, significantly without changing the potassium concentration in the blood serum. Goraya and colleagues studied 77 patients with stage 4 LIL complicated by metabolic acidosis. The treatment of study participants was randomly supplemented with fruits and vegetables or sodium bicarbonate. The plant products provided were alkaline and rich in potassium, such as oranges, potatoes, spinach, and tomatoes. The researchers concluded from this study that increased consumption of fruits and vegetables did not affect blood serum potassium concentration (none of the patients exceeded the 5 mmol/l threshold). However, they observed a positive trend in the indicators reflecting kidney damage. In summary, given that fruits and vegetables have a 50-60% biological availability of potassium, incorporating them into the diet can benefit a patient with LIL. It can positively impact their blood pressure, correct developed metabolic acidosis, and lower the risk of further kidney damage, all while maintaining a normal potassium concentration in the blood serum.

As food suppliers are encouraged to reduce the sodium content in their products, representatives of this industry have started to increasingly seek suitable alternatives, hence potassium additives are being used more frequently. This poses a number of problems for patients with LIL who are on a potassium-restricted diet, for example, in Canada, all dialysis patients are recommended to limit their sodium intake. The biological availability of potassium additives has been most extensively studied in 2 randomized, single-blind, crossover trials. Braschi and his team assessed the absorption of potassium chloride from potassium-fortified bread by the participants. The researchers found that this food additive is completely absorbed in the digestive tract. Similar results were obtained by the Macdonald-Clarke research team: the participants were given increasing doses of potassium gluconate, and the amount of potassium excreted in the urine was monitored. It was found that in all doses, about 94% of the consumed potassium was excreted in the urine. These findings provide a strong logical basis that the biological availability of these substances differs little from phosphorus-containing additives. Recently, the use of potassium supplements in food has been started to be investigated. A group of researchers, after conducting a survey, examined the products most commonly consumed by dialysis patients in Canada [21]. It turned out that 76 out of 91 products contained various types of food additives: 37% of them had phosphorus, but in 9% of cases, potassium compounds were also used. Therefore, every eleventh patient undergoing dialysis consumes a food product containing potassium additives. Another important observation related to this topic is that in products containing potassium additives, the amount reaches about 900 mg/100 g, compared to products without them - 325 mg/100 g. Products with nearly 3 times more potassium per 100 g compared to the reference standard allow for a preliminary conclusion that a large amount of this substance can be obtained even from non-traditional sources. It is crucial for patients and doctors aiming to effectively avoid hyperkalemia to identify these high-potassium products. In another study conducted in Canada, 38 meat or poultry products were examined: half of them were natural, and half had less sodium [4]. Analysis results: products with less sodium were found to have 44% more potassium. Although the potassium content varied significantly among products, one of them exceeded all average values - 100 g contained as much as 1,500 mg of potassium. This is a significantly excessive amount for patients who need to limit potassium intake. Such differences in the amount of food additives suggest that they can be found anywhere, so it is essential to carefully choose products. In 2009, a similar study was conducted in the United States as in Canada [22]. The results were practically the same: 36 meat and poultry products showed 2-3 times higher potassium levels than before, with the highest values reaching 930 mg/100 g. Since the food industry is required to reduce sodium content, it is likely that more products containing potassium additives will be produced. There is a high probability that this change will affect patients with CKD. Nevertheless, the idea of a solution is: one study examined the effect of education about phosphorus additives on its concentration in blood serum. The results are promising - the values decreased by 10 mg/l [12]. The only concerning thing is that it is unclear how effective this will be regarding potassium additives.

Practical Application

Since the biological availability of potassium in natural fruits and vegetables can be as low as 50-60%, there is a lack of evidence linking high consumption of fruits and vegetables with high potassium concentration in the blood serum. Moreover, diets rich in fruits and vegetables may even improve other health indicators related to CKD. It is believed that the biological availability of potassium in food additives can reach up to 100%, but this is rarely discussed in educational sources or dietary guidelines. Potassium additives can increase the potassium content in consumed food by 2-3 times. Restricting fruits and vegetables to control potassium concentration in the blood serum may not only fail to achieve the desired result but also eliminate beneficial food products from the diet. Reviews of potassium additives should be included in patient education programs, as these substances provide the highest biologically available potassium content in the body.

REFERENCES

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Publication "Kidney and Cardiovascular Diseases" 2019.