# Association between serum phosphate levels within the normal range and all-cause mortality among US adults

## TL;DR

This study found that higher-normal phosphate levels are linked to increased mortality in people with chronic kidney disease but not in the general population.

## Contribution

The study reveals that phosphate levels within the normal range may still impact mortality risk in individuals with CKD.

## Key findings

- Higher-normal phosphate levels were not associated with increased mortality in the general population.
- In individuals with CKD, higher-normal phosphate levels were linked to a 13% increased mortality risk.
- No association was found between higher-normal phosphate and mortality in those without CKD.

## Abstract

Hyperphosphatemia is associated with increased mortality in chronic kidney disease (CKD), but the clinical relevance of variation within the normal serum phosphate range remains unclear. This study evaluated the association between higher-normal serum phosphate levels within the normal range and all-cause mortality among US adults.

We conducted a cohort study using data from 15 848 individuals aged ≥20 years with serum phosphate levels between 2.5 and 4.5 mg/dL from the Third National Health and Nutrition Examination Survey (1988-1994) linked to mortality data ascertained by the National Center for Health Statistics with the National Death Index through December 2019. Baseline serum phosphate was the exposure. Participants were categorized into lower-normal (2.5 mg/dL to <3.5 mg/dL; n = 7691) and higher-normal (3.5 mg/dL to ≤4.5 mg/dL; n = 8157) serum phosphate groups. Cox proportional hazard models were used to estimate adjusted hazard ratios (aHR) for all-cause mortality. A subgroup analysis was conducted by CKD status (estimated glomerular filtration rate ≥60 and <60 mL/min/1.73 m2).

Over a median follow-up of 26.3 years, 6660 (42%) participants died. Compared to the lower-normal group, the higher-normal group showed no significant increase in all-cause mortality risk in the overall population (aHR 1.06 [95% CI, 0.98-1.13]). However, among individual with CKD, higher-normal serum phosphate was significantly associated with increased all-cause mortality (aHR 1.13 [95% CI, 1.02-1.25]), wheres no association was observed in those with estimated glomerular filtration rate ≥60 mL/min/1.73 m2 (aHR 1.01 [95% CI, 0.92-1.12]; P for interaction, .14).

Higher-normal phosphate levels were associated with an increased risk of all-cause mortality among people with CKD.