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 Ͻ 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.

Explaining the Racial Difference in AKI Incidence

“…17 Income might also affect outcomes of kidney disease, since the probability of anemia, phosphatemia, disability, depression, and cardiovascular disease was greater among those patients with low income. [18][19][20][21][22][23][24] Our study adds to this body of evidence by providing new data relating AKI (which itself is both a risk factor for and an outcome of CKD 25,26 ) to low income.…”

Chronic Renal Insufficiency Cohort Study (CRIC)

“…An independent association was found between race and serum phosphate that was modified by income level. In the highest income stratum, blacks had significantly higher serum phosphate levels than whites, whereas in the lowest stratum (,$20,000/yr), there was no significant difference in serum phosphate levels by race (6). These findings underscore how socioeconomic disparities can influence metabolic parameters.…”

Fibroblast Growth Factor 23, Cardiovascular Disease Risk Factors, and Phosphorus Intake in the Health Professionals Follow-up Study

“…It is also possible that differences in the dietary habits of the two populations may have played a role. The participants of the CRIC Study included a much larger proportion of individuals with low socioeconomic status than the participants of this study (28), all of whom were health professionals. Because less affluent individuals generally consume higher quantities of foods containing inorganic phosphorus additives incompletely captured by standard dietary surveys (29), this may have increased imprecision in the ascertainment of phosphorus intake in CRIC participants, further limiting the ability to detect an association of dietary phosphorus with FGF23 in the CRIC Study.…”