Relationship of dietary phosphate intake with risk of end stage renal disease and mortality in chronic kidney disease stage 3-5: A Modification of Diet in Renal Disease study

KDIGO guidelines recommend dietary phosphate restriction to lower serum phosphate levels in CKD stage 3-5. Recent studies suggest that dietary phosphate intake is only weakly linked to its serum concentration, and the relationship of phosphate intake with adverse outcomes is uncertain. To further evaluate this, we used Cox proportional hazards models to assess associations of baseline 24 hour urine phosphate excretion with risk of end stage renal disease (ESRD), all-cause mortality, and mortality subtypes (cardiovascular disease (CVD) and non-CVD) using the Modification of Diet in Renal Disease data. Models were adjusted for demographics, CVD risk factors, iothalamate GFR, and urine protein and nitrogen excretion. Phosphate excretion was modestly inversely correlated with serum phosphate concentrations. There was no association of 24 hour urinary phosphate excretion with risk of ESRD, CVD-, non-CVD- or all-cause mortality. For comparison, higher serum phosphate concentrations were associated with all-cause mortality (hazard ratio per 0.7 mg/dL higher, 1.15 [95% CI 1.01, 1.30]). Thus, phosphate intake is not tightly linked with serum phosphate concentrations in CKD stage 3-5, and there was no evidence that greater phosphate intake, assessed by 24 hour phosphate excretion, is associated with ESRD, CVD-, non CVD-, or all-cause mortality in CKD stage 3-5. Hence, factors other than dietary intake may be key determinants of serum phosphate concentrations and require additional investigation.