making. The survey relies on the gold standard for dietary measures, two or more 24-hour dietary recalls per person (IOM, 2000). NHANES is unique in that it collects and tracks both dietary intake and health measures in a nationally representative sample of Americans. Dietary intake estimates are limited by survey respondents’ abilities to accurately report foods and amounts consumed and by the accuracy, specificity, and currentness of the food composition databases used to code foods reported in the survey. They are also prone to underreporting intake (IOM, 2000). Issues related to estimation of usual intake related to WWEIA-NHANES have been carefully reviewed by others (Dwyer et al., 2003).
During the four decades that dietary intake has been tracked in nationally representative cross-sectional surveys of the population, there have been changes in the data collection methods and protocols used to estimate dietary intake. The quality of data has improved, but of course some bias and measurement error still exist given that the estimates must rely on self-reported data. Beginning with NHANES III (1988–1994), improvements were made in dietary data collection to produce population-level estimates of total sodium intake to track progress in meeting Healthy People objectives for the dietary guidelines for sodium.2 These improvements included the collection of more than 1 day of intake on at least a subsample of the population and questions about tap water consumption and water softening, dietary supplement use, and salt added at the table, including the type of salt. These additional survey questions were intended to produce more complete estimates of dietary sodium intake.
Beginning in 2003–2004, two 24-hour diet recalls were collected and released for each person, allowing for estimates of usual nutrient (sodium) intake in the population using statistical software to account for the large day-to-day variations in individual intake (Dodd, 1996). The improvements in dietary data collection and the availability of statistical techniques to assess dietary intake allow for estimates of the population’s usual sodium intake from food sources. When the available statistical software is not applicable to the measure(s) of interest, data on the basis of a 1-day mean are reported. This applies to analyses focused on food categories, sodium intake from earlier studies, and measures of sodium density.
Current estimates of intake are derived from information available from two recently completed NHANES: 2003–2004 and 2005–2006. Those data sets were combined for this report to provide larger sample sizes for
Available online: http://www.healthypeople.gov/document/pdf/tracking/od19.pdf (accessed November 14, 2009).