Hyperphosphatemia is one of the common and serious problems that nephrologists encounter when treating dialysis patients; it is associated with the development of secondary hyperparathyroidism, mineral bone disorder, and vascular stiffening and calcification [1,2]. The exact mechanisms for these issues are unclear, but several studies have reported that serum phosphate stimulates transformation of vascular smooth muscle cells into osteoblasts. Separately, hyperphosphatemia leads to endothelial dysfunction and elevated fibroblast growth factor 23, which contributes to left ventricular hypertrophy, coronary artery disease, and mortality [3]. Therefore, serum phosphate level needs to be maintained in an adequate range. However, only about 50% of dialysis patients maintain their phosphate levels within the target range of between 3.5 mg/dL and 5.5 mg/dL as suggested by the Kidney Disease Outcome Quality Initiative [4].

There are four major ways to manage phosphate level: via dialysis, dietary restriction, oral phosphate binders, and control of hyperparathyroidism. Phosphorous can be partially removed by dialysis; three-times weekly conventional hemodialysis sessions can remove from 300 to 1,200 mg of phosphorous per session [3,5]. Regular Western diets contain 1,500 mg daily phosphorus, equivalent to 10,500 mg per week, so hemodialysis reduces dietary phosphate intake to a net of 6,900 mg per week, reflecting the limited efficacy of phosphate removal by dialysis [1,5]. To solve this imbalance, phosphate binder is commonly used to remove extra phosphorus from the body. However, drug compliance is a key for obtaining any benefit from phosphate binder because, for optimal efficacy, the binder must be taken at the correct time, right after meals. Therefore, education on dietary phosphate restriction and the proper usage of phosphate binder is important. However, excessively stringent dietary restrictions may lead to malnutrition [2,6–9], so education is particularly necessary regarding maintaining good protein intake with less phosphate. The aim of this study was to evaluate the efficacy of education on low-phosphate diet and proper phosphate binder intake.

The primary purpose of this study was to determine how many patients could achieve a calcium-phosphate product of less than 55 through dietary consultation and pharmacological education. After three months, 75.0% of patients in the education group achieved the primary goal as compared with 72.7% of control group. Meta-analyses have investigated the percentages of patients who reached phosphorus levels of less than 5.5 mg/dL after dietary education. Caldeira et al [13] in their meta-analysis reported that 50% of the education group of analyzed studies attained less than 5.5 mg/dL, whereas none of the controls were able to reach this goal. In the education groups in this meta-analysis, the authors observed a decrease of 0.75 mg/dL in phosphorus levels. In another meta-analysis, all of the included studies except one reported lower serum phosphorus. The changes in phosphorus level ranged from 0.3 to 1.6 mg/dL and eight of the studies achieved a serum phosphorus target of ≤ 5.5 mg/dL after education [14]. We did not observe a declining decrement of the phosphorus level following the intervention in this study, likely because the serum phosphorus was already in the target range before and after the study as compared with in the other studies in which many patients’ phosphorus levels exceeded 5.5 mg/dL before the studies [15].

Total dietary phosphorous intake did not change after the intervention in this study. In other reports, dietary nonadherence in patients undergoing maintenance hemodialysis ranged from 9% to 80.4% [16,17]. It is generally known that hemodialysis patients are less likely to adhere to dietary phosphate restrictions versus other restrictions such as those for sodium or potassium because they are less educated about diet itself and the consequences of hyperphosphatemia [15,18]. However, of note, in the present study, education reduced the dietary phosphate-to-protein ratio and this lower ratio is important because high ratios are related with increased mortality [2]. Low ratios are also important because they indicate that the patients maintained their overall nutritional statuses and dietary protein intake even though they reduced their phosphate intake. Therefore, information on the phosphate-to-protein ratios in different foods should be a mainstay of education [19] so that patients can identify foods that have high protein but low phosphorus content [7]. In the absence of specific foods, education should focus on reducing processed foods, which contain inorganic phosphorus. In a previous report, 46% of hemodialysis patients did not know that preservatives that contain phosphate are added extensively to processed foods and only 25% of patients were aware of the presence of phosphate in soda [20]. In a previous study, dietitian-led education reduced consumption of phosphorus-containing food additives [21], while another study showed that reducing the intake of processed food was one of the most effective ways of controlling hyperphosphatemia [17].

Education in this study increased patients’ knowledge of when to take phosphate binder, although the increase was not statistically significant. Notably, the absolute percentage of patients who showed better knowledge after education was higher in the education group. However, as Reddy et al [15] and Elliott et al [18] found, improving patient knowledge did not lead to actual changes in mean serum phosphate levels. In a study that investigated patients’ pill-taking habits, only 50% of the patients took phosphate binders correctly [16]. Separately, because there is a high demand for more information about phosphate binders [22], proper education should be provided to those who need and want it.

Pharmacologic education did not change the MMAS-8 score. Poor adherence to phosphate binder use and dietary restrictions is relatively common among maintenance hemodialysis patients [5]. Several studies revealed that overall medication nonadherence in these patients ranges from 9.7% to 49.5% and that as many as 87% of patients have reported not adhering to their phosphate binder prescriptions [16,17]. Many factors cause this poor adherence. Patients’ ethnic backgrounds, education levels, subjective health statuses, and beliefs about whether they even need the phosphate binder, along with the complexity of some patients’ pharmaceutical regimens, influence their adherence [6,18]. Separately, hemodialysis patients face large pill burdens that primarily comprise phosphate binders. The median number of pills per day for hemodialysis patients in the United States is 19 and phosphate binders account for nearly half of that daily burden [23]. Another cause is forgetfulness; in another study, 64% of survey respondents did not take their pills as prescribed because they forgot, while 35% did not do so because of financial issues [5]. Some reasons for poor adherence can be modified through education, but some cannot.

There are several limitations in this study. First, our study was small and designed to detect a 75% reduction in the number of patients with a calcium-phosphate product of more than 55, which we did not achieve. Second, because we conducted our investigation in a single hemodialysis unit, information might have been transferred between the two groups, which might have reduced the differences between the educated and non-educated groups. Third, food labels in Korea lack information on phosphate content, which might hinder the efficacy of phosphate restriction education. Fourth, the intervention group was offered education only a single time and, finally, we assessed nutritional status based on dietary recall, which could have underestimated actual intake and inevitably has a wide range of variability [9].

In the present study, education did not improve calcium-phosphate product. However, education partly corrected proper timing of phosphate binder intake and partly lowered the phosphate-to-protein ratio from dietary intake, in spite of statistical insignificance. These findings imply the importance of continuous and individualized educational efforts to reduce serum phosphorus levels.