Serum phosphorus concentrations in the third National Health and Nutrition Examination Survey (NHANES III)

Abstract

Background: Higher serum phosphorus concentrations within the normal laboratory range have been associated with cardiovascular events and mortality in large prospective cohort studies of individuals with and without kidney disease. Reasons for interindividual variation in steady-state serum phosphorus concentrations are largely unknown.

Study design: Cross-sectional study.

Setting & participants: 15,513 participants in the Third National Health and Nutrition Examination Survey.

Predictors: Demographic data, dietary intake measured by means of 24-hour dietary recall and food-frequency questionnaire, and established cardiovascular risk factors.

Outcome & measurements: Serum phosphorus concentration.

Results: Mean serum phosphorus concentrations were significantly greater in women (+0.16 mg/dL versus men; P < 0.001) and people of non-Hispanic black and Hispanic race/ethnicity (+0.06 and +0.07 mg/dL versus non-Hispanic white, respectively; P < 0.001). Dietary intakes of phosphorus and phosphorus-rich foods were associated only weakly with circulating serum phosphorus concentrations, if at all. Higher serum phosphorus levels were associated with lower calculated Framingham coronary heart disease risk scores, which are based on traditional atherosclerosis risk factors. In aggregate, demographic, nutritional, cardiovascular, and kidney function variables explained only 12% of the variation in circulating serum phosphorus concentrations.

Limitations: Results may differ with advanced kidney disease.

Conclusions: Serum phosphorus concentration is weakly related to dietary phosphorus and not related to a diverse array of phosphorus-rich foods in the general population. Factors determining serum phosphorus concentration are largely unknown. Previously observed associations of serum phosphorus concentrations with cardiovascular events are unlikely to be a result of differences in dietary intake or traditional cardiovascular risk factors.

Figure 1

Distribution of serum phosphorus concentrations in the Third National Health and Nutrition Examination Survey. Serum phosphorus in mg/dL may be converted to mmol/L by multiplying by 0.3229.

Figure 2

Mean serum phosphorus concentrations by time of day and fasting status. Open circles, fasting; filled circles, nonfasting; bars, 95% confidence intervals. Serum phosphorus in mg/dL may be converted to mmol/L by multiplying by 0.3229.

Figure 3

Mean serum phosphorus concentrations by age, sex, and race/ethnicity. Bars represent 95% confidence intervals. Abbreviations: NHW, non-Hispanic white; NHB, non-Hispanic black; H, Hispanic. Serum phosphorus in mg/dL may be converted to mmol/L by multiplying by 0.3229.

Figure 4

Relationship of serum phosphorus concentration to 24-hour dietary phosphorus, total energy, and percentage of protein intake. Serum phosphorus in mg/dL may be converted to mmol/L by multiplying by 0.3229.