Abstract and Introduction
Purpose of review The role of nutrition and nutritional supplementation in dialysis recently has been reinvigorated, with small clinical trials exploring surrogate outcomes and larger epidemiologic studies generating treatment hypotheses requiring further study. The present review focuses on major aspects of nutrition and outcomes in hemodialysis patients: protein and calorie intake and nutritional vitamin D supplementation.
Recent findings Building on data from small studies, two large, quasi-experimental cohort studies showed significant mortality benefits associated with oral nutritional supplements provided during dialysis, suggesting potential options for ameliorating the protein-energy wasting that is common in dialysis patients and associated with poor outcomes. Multiple cohort studies suggest, both in the general population and in dialysis, that higher 25(OH) vitamin D levels are associated with improved outcomes; however, no major mortality trials exist in dialysis, and the smaller, surrogate studies conducted to date have been disappointing, showing no consistent benefits in surrogate outcomes including inflammation and anemia, despite appropriate responses of vitamin D levels to repletion.
Summary Nutritional interventions are attractive options for improving outcomes in dialysis patients. Nutritional protein supplements have considerable promise, but require further study, preferably in a large, generalizable pragmatic trial. Small nutritional vitamin D supplementation trials in dialysis have had disappointing results. In the absence of new data, there appears to be no role for routine assessment or repletion of 25(OH) vitamin D deficiency or insufficiency in dialysis.
'It is necessary for a physician to know… what man is in relation to what he eats and drinks, and in relation to his habits generally, and what will be the effect of each upon each individual'.
- Ancient Medicine 20 (attributed to Hippocrates)
Over the past several years, the role of nutrition and nutritional supplementation in dialysis has been reinvigorated, moving from a topic deemed to be within the purview of only dieticians to a key modifiable factor that may improve the overall health status of all dialysis patients, and that warrants attention from the entire dialysis team. It has long been recognized that poor nutritional status, whether defined by wasting and cachexia or by nonspecific markers of nutritional and health status, such as albumin, is associated with increased morbidity and mortality in dialysis patients. In their seminal 1990 article, Lowrie and Lew evaluated the relationship between predialysis serum chemistries and survival, noting a marked relationship between low serum albumin level and all-cause mortality. In that study, strong associations with an increased risk of mortality also were seen with lower levels of cholesterol, urea nitrogen, creatinine, potassium, and phosphorus. In a more contemporary revisiting of Lowrie and Lew's work, Lacson et al. similarly noted a 177% increased risk of death and 67% increased risk of hospitalization per 1 g/dl decrease in albumin level, calling on quality improvement efforts to target potentially actionable patient variables, including serum albumin level.
Broadly speaking, nutritional status denotes more than just protein and calories, it also refers to essential nutrients and vitamins that are consumed either in the diet or as supplements. Dialysis, in addition to clearing uremic toxins, also removes amino acids, peptides, and water-soluble vitamins. There are no U.S. guidelines that review vitamin use in adult dialysis patients, although the 2000 National Kidney Foundation (NKF) Kidney Disease Outcomes Quality Initiative (KDOQI) Nutrition in Chronic Renal Failure Guideline does discuss whether there is a role for carnitine supplementation. Similarly, because of a paucity of data, the European Best Practice Guideline (EBPG) on Nutrition, published in 2007, offers expert opinion in lieu of a recommendation for vitamins, minerals, and trace elements administration in maintenance of hemodialysis patients.
Although not truly a vitamin, vitamin D intake and supplementation has become an increasing topic of research, and testing for and treating vitamin D deficiency and insufficiency is widespread, despite little evidence of the benefit of supplementation on hard clinical outcomes. In dialysis, nutritional vitamin D [ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3)] supplementation had received little attention until recently, reflecting existing conceptions that, without 1-α hydroxylation by the kidneys, vitamin D would have little effect on health. This resulted in no recommendation regarding nutritional D use in patients treated with dialysis in the 2009 Kidney Disease Improving Global Outcomes (KDIGO) Mineral and Bone Disorder Guideline.
Curr Opin Nephrol Hypertens. 2015;24(6):546-556. © 2015 Lippincott Williams & Wilkins