Low socioeconomic status associates with higher serum phosphate irrespective of race

Abstract

Hyperphosphatemia, which associates with adverse outcomes in CKD, is more common among blacks than whites for unclear reasons. Low socioeconomic status may explain this association because poverty both disproportionately affects racial and ethnic minorities and promotes excess intake of relatively inexpensive processed and fast foods enriched with highly absorbable phosphorus additives. We performed a cross-sectional analysis of race, socioeconomic status, and serum phosphate among 2879 participants in the Chronic Renal Insufficiency Cohort Study. Participants with the lowest incomes or who were unemployed had higher serum phosphate concentrations than participants with the highest incomes or who were employed (P < 0.001). Although we also observed differences in serum phosphate levels by race, income modified this relationship: Blacks had 0.11 to 0.13 mg/dl higher serum phosphate than whites in the highest income groups but there was no difference by race in the lowest income group. In addition, compared with whites with the highest income, both blacks and whites with the lowest incomes had more than twice the likelihood of hyperphosphatemia in multivariable-adjusted analysis. In conclusion, low socioeconomic status associates with higher serum phosphate concentrations irrespective of race. Given the association between higher levels of serum phosphate and cardiovascular disease, further studies will need to determine whether excess serum phosphate may explain disparities in kidney disease outcomes among minority populations and the poor.

Figure 1.

Relationship between race and serum phosphate is modified by income. Black boxes represent mean values for the overall sample within each stratum of income, filled circles represent mean values for blacks, and open circles represent mean values for whites. Vertical lines represent SD.

Figure 2.

Odds of hyperphosphatemia (>4.6 mg/dl) increase in blacks and whites with decreasing income. Filled bars represent blacks and open bars represent whites. Vertical lines represent 95% confidence intervals. Whites in the highest income level are the referent group in both models. The multivariable model was adjusted for age, gender, diabetes, eGFR, and activated vitamin D and phosphorus binder use.