Dietary and Pharmacological Control of Calcium and Phosphate Metabolism in Dialysis Patients

Abstract

Chronic kidney disease-mineral and bone disorder is a new term defining a complex syndrome which underlines the need of a systemic approach to disturbances of calcium and phosphate metabolism in patients with renal failure. In recent years, the availability of new phosphorus binders and the appearance of new selective vitamin D receptor activators and calcimimetics have increased our current armamentarium and have changed previous paradigms. All these drugs can be used in combination, acting in distinct yet complementary pathways, with a resultant improvement in their individual clinical profile and reduction in secondary effects, while enhancing the achievement of clinical guideline targets. On the other hand, we should be aware that treatment costs are increasing and most of our knowledge is opinion-based. In this article, we shall consider rational recommendations on the control of calcium, phosphorus and parathyroid hormone while awaiting new evidence. We shall also briefly review some important related issues such as vascular calcification, adynamic bone disease, osteoporosis and the need of parathyroidectomy. Future guidelines may modify current recommendations, but we believe that the lack of an absolute evidence is not equivalent to the lack of awareness of the important problem which chronic kidney disease-mineral and bone disorder represents.

Stirring the Pot: Can Dietary Modification Alleviate the Burden of CKD?

“…As kidney function declines, there is a decrease in the number of functioning nephrons and subsequent decrease in phosphorus excretion [102]. As renal function decreases to less than 80% of normal, phosphorus absorption can exceed the rate of clearance by the kidneys, and a subsequent rise in serum phosphate levels is seen [61,103].…”

“…Humans (and other monogastric animals) lack the enzyme phytase and thus cannot digest phytate, although some degradation may occur via the intestinal microbiota [119]. Dairy products have about 30%–60% bioavailability, and the highest bioavailability of organic phosphate, in meat products, may be as high as 80% [102]. This difference in phosphorus bioavailability between meat and plant protein sources, may partially explain the benefits of consuming a greater proportion of protein from plants sources, as described above.…”

“…These additives are primarily inorganic phosphate salts that require no enzymatic digestion and dissociate rapidly in the low pH environment of the stomach; thus inorganic phosphate additives have a high bioavailability of 90%–100% [102]. Phosphoric acid, which is present in cola drinks, has a bioavailability of 100% [121].…”

“…An observational prospective five year study found that haemodialysis patients with higher dietary phosphate:protein ratio had increased mortality, even after serum phosphate levels were controlled for [117]. Egg white has one of the lowest phosphate:protein ratios [102] whilst many processed foods and beverages are high in phosphate with low protein. One study compared the phosphate:protein ratio in meat products prepared with and without phosphate additives found that there was a 60% increase in the phosphate:protein ratio in those products containing additives [131].…”

Mineral and bone disorders in chronic kidney disease and end-stage renal disease patients: new insights into vitamin D receptor activation

“…4 As therapy with VDR activators appears to be useful in preventing bone loss and in decreasing morbidity and mortality, across different biochemical mineral metabolism parameters, some consider vitamin D and/or selective VDR activation to be essential therapy in CKD regardless of bone turnover status. 29, 106 It is conceivable that other beneficial effects of activation of the VDR beyond bone result in some benefit even in the presence of ABD. 17 However, the current Kidney Disease Outcomes Quality Initiative and KDIGO recommendations limit the administration of VDR activators for the treatment of hyperparathyroidism only.…”