Dialysis Patients Exhibit Abnormal Postprandial Mineral Handling
Excess calcium following a meal may be deposited in soft tissue and blood vessels, researchers hypothesize.
Mineral and hormonal responses to a meal differ between patients on maintenance hemodialysis (HD) and healthy controls, investigators found.
Mark Reinhard, MD, PhD, of Aarhus University in Denmark, and his team tested mineral handling in 12 HD patients and 12 matched healthy controls on a non-dialysis day for 9 hours after consumption of a standard meal (a turkey or chicken salad sandwich with skim milk, coffee, and tea). None of the patients had taken phosphate binders for 24-hours prior to the test, and all had fasted.
Results published in the Journal of Renal Nutrition showed that the healthy individuals responded to the mineral load with increased urinary excretion of calcium and phosphate accompanied by changes in parathyroid hormone (PTH) levels. The maximum amount of phosphate was excreted when PTH reached its zenith at 300 minutes after the meal. Overall, plasma calcium and phosphate levels did not change significantly from baseline levels before the meal.
HD patients also had peak PTH levels of 11% above baseline at 300 minutes after the meal. Unlike controls, however, their plasma phosphate levels declined from 60 to 120 minutes after the meal by up to 10% from baseline.
Fibroblast growth factor-23 (FGF23) did not appear to respond immediately to the meal. FGF23 did not change in HD patients, but it decreased 16% below baseline values in healthy controls.
“In HD patients, the mineral load paradoxically induced a decrease in plasma phosphate, whereas ionized calcium remained unchanged although PTH increased,” Dr Reinhard and his colleagues stated. “These findings suggest that excess calcium and phosphate may be disposed of by mineral deposition, which may include soft tissue and vascular calcification.”
The results are in line with other recent studies. The team advised clinicians to educate advanced kidney disease patients on dietary guidelines to limit calcium and phosphate intake to reduce the risks for calcification and cardiovascular disease.
Reinhard M, Frystyk J, Randers E, Martin Bibby B, and Ivarsen P. Postprandial mineral handling in patients on maintenance hemodialysis. J Ren Nutr. DOI: 10.1053/j.jrn.2017.11.003