Lower calcitriol levels tied to rapid loss of kidney function among older adults
Older adults with lower calcitriol concentrations are at greater risk of kidney function decline, a study has shown.
The 10-year case-control study included a subcohort of 479 well-functioning community-living older adults aged 70–79 years at baseline from the Health ABC Study, 397 patients with major kidney function decline and 207 patients with incident heart failure (HF). Calcitriol concentrations, measured at the 2-year follow-up visit using positive ion electrospray ionization-tandem mass spectrometry, were examined in relation to kidney function decline (≥30 percent decline in estimated glomerular filtration rate [eGFR] from baseline), HF and all-cause mortality.
During a mean follow-up of 8.6 years, 212 (44 percent) subcohort participants died. Multivariable Cox regression models showed that the risk of major kidney function decline increased by 30 percent per 1–SD lower calcitriol concentration (hazard ratio [HR], 1.30; 95 percent CI, 1.03–1.65; p=0.03).
Calcitriol was significantly associated with neither incident HF (HR, 1.16; 0.94–1.47) nor mortality (HR, 1.01; 0.81–1.26). Furthermore, no significant interactions were observed between calcitriol concentrations and chronic kidney disease status, baseline intact parathyroid or fibroblast factor 23 concentrations.
Researchers cited several mechanisms that potentially explain why individuals with lower eGFRs have reduced calcitriol concentrations. First, reduced kidney mass functioning may limit the kidney’s ability to convert 25-hydroxyvitamin D to calcitriol. Second, lower eGFR may lead to limited delivery of substrate to the 1α-hydroxylase enzyme. Third, those with chronic kidney disease often have high FGF-23 levels, which may inhibit 1α-hydroxylase activity. [Kidney Int 2002;62:1672-1681; Curr Opin Lipidol 2002;13:255-260]
Additional investigations must be conducted to elucidate whether serum calcitriol measurement provides a surrogate for kidney tubule function and may facilitate assessment of nonglomerular aspects of kidney health, researchers said.