Abstract
Purpose of ReviewThe kidneys play a critical role in the balance between the internal milieu and external environment. Kidney failure is known to disrupt a number of homeostatic mechanisms that control serum calcium and normal bone metabolism. However, our understanding of calcium balance throughout the stages of chronic kidney disease is limited and the concept of balance itself, especially with a cation as complex as calcium, is often misunderstood. Both negative and positive calcium balance have important implications in patients with chronic kidney disease, where negative balance may increase risk of osteoporosis and fracture and positive balance may increase risk of vascular calcification and cardiovascular events. Here, we examine the state of current knowledge about calcium balance in adults throughout the stages of chronic kidney disease and discuss recommendations for clinical strategies to maintain balance as well as future research needs in this area.Recent FindingsRecent calcium balance studies in adult patients with chronic kidney disease show that neutral calcium balance is achieved with calcium intake near the recommended daily allowance. Increases in calcium through diet or supplements cause high positive calcium balance, which may put patients at risk for vascular calcification. However, heterogeneity in calcium balance exists among these patients.SummaryGiven the available calcium balance data in this population, it appears clinically prudent to aim for recommended calcium intakes around 1000 mg/day to achieve neutral calcium balance and avoid adverse effects of either negative or positive calcium balance. Assessment of patients’ dietary calcium intake could further equip clinicians to make individualized recommendations for meeting recommended intakes.
Highlights
Patients with chronic kidney disease (CKD) have marked disruption in bone and mineral metabolism resulting in a complex disorder that has been termed CKD-mineral bone disorder (CKD-MBD)
The purpose of this review is to examine the available literature on calcium balance in CKD, discuss knowledge gaps and the future research needs in this area, and propose practical recommendations based on current available evidence
It is clear that with advancing kidney disease, the kidneys are no longer able to increase urine calcium excretion, and this removes an important safety mechanism to prevent calcium excess in patients with CKD. It is well-known that 1,25-hydroxyvitamin D (25D) levels fall with advancing CKD and intestinal calcium absorption becomes increasingly dependent on a positive gradient to maintain even neutral flux, as calcium can be both absorbed and lost via the gastrointestinal tract
Summary
Patients with chronic kidney disease (CKD) have marked disruption in bone and mineral metabolism resulting in a complex disorder that has been termed CKD-mineral bone disorder (CKD-MBD). Decreased calcium absorption and decreased urinary calcium excretion are observed, as well as heterogeneous bone disease and excessive vascular and soft tissue calcification. The underlying disease process is not completely understood, the initiators of the observed abnormalities are unclear, and definitive therapies are lacking. Both negative and positive calcium balance pose potential health threats in CKDMBD: negative balance may increase risk for osteoporosis and fracture, and positive balance may increase risk for. It is unlikely that negative or positive calcium balance alone is the initiating factor and it is unproven, clinically plausible, that negative or positive calcium balance contributes to CKD-MBD disease progression in adults. The purpose of this review is to examine the available literature on calcium balance in CKD, discuss knowledge gaps and the future research needs in this area, and propose practical recommendations based on current available evidence
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