Assessing U.S. Sodium Intake through Dietary Data and Urine Biomarkers

Abstract

Sodium intake is related to blood pressure, an established risk factor for heart disease and stroke. Reducing intake may save billions in United States health care dollars annually. Efforts targeting sodium reductions make accurate monitoring vital, yet limited information exists on the accuracy of the current data to assess sodium intake in the United States population. In this symposium, new findings were presented on the accuracy of estimating population 24-h urinary excretion of sodium from spot urine specimens or sodium intake from 24-h dietary recalls. Differences in accuracy by sex, BMI, and race were apparent as well as by timing of spot urine collections. Although some published equations appear promising for estimating group means, others are biased. Individual estimates of sodium intake were highly variable and adjustment for within-individual variation in intake is required for estimating population prevalence or percentiles. Estimates indicated United States sodium intake remains high.

Applying recovery biomarkers to calibrate self-report measures of sodium and potassium in the Hispanic Community Health Study/Study of Latinos

“…However, the use of 24-hour urinary excretion to assess individual, as opposed to population intake is not without limitations. Consistency of intake, physical activity, ambient heat, humidity and circadian rhythms impact the excretion of sodium and potassium (20) and there may be more variability in potassium than sodium excretion related to racial differences (21). More recently, spot urine collections that take into account timing of collection and race-ethnicity, have also been used, but are reported to be a less accurate estimate than 24-hour urine (20, 22).…”

The Science of Salt: A Regularly Updated Systematic Review of Salt and Health Outcomes (June and July 2015)

“…A systematic review of the relationship of salt intake estimated from spot urine samples to 24‐hour urine samples found a wide range of correlations from very weak to strong . Further, the formula used for estimating sodium intake often incorporates age, sex, urinary creatinine, height, and weight and hence the estimate of salt intake is confounded by those factors that are also associated with many common health issues . Many factors impact short‐term sodium and creatinine excretion, apart from dietary salt, and hence estimates from a spot urine sample are a complex reflection of many inputs.…”

Understanding the science that supports population‐wide salt reduction programs

“…Several of the studies showing a J‐shaped relationship between salt intake and health outcomes rely on a single spot urine assessment to estimate each person's long‐term usual sodium intake . Single spot urine sodium samples cannot accurately assess an individual's usual salt intake, because sodium intake varies meal to meal and day to day and is also impacted by seasonal food availability . Other studies have had a large proportion of 24‐hour urine collections that were incomplete, leading to inaccurate estimates of salt intake that would impact the results .…”

“… Salt intake varies from day to day and from meal to meal . Therefore, the sodium content of a spot urine sample reflects what was just eaten rather than usual salt intake over an extended period in an individual Other factors affect spot urine sodium excretion concentration and include state of hydration, posture, renal function, diurnal variation, and other regulatory functions …”