As shown in Figure 2-14, the differences in sodium intake that were observed among children and adult men and women disappear to a large degree when the intakes are expressed as sodium densities. This suggests that the intake differences among life stage groups at any time were related primarily to differences in their energy intake rather than to differences in the sodium densities of the foods they consumed. The increasing sodium densities between the 1970s and late 1980s also show that foods as consumed contained higher amounts of sodium between those time periods. However, since the early 1990s sodium densities appear to be stable. Although data are not available to allow the separation of the relative contribution of increasing energy intake over time (or improved measures of energy intake over time) from the relative contribution of increasing amounts of sodium in foods over time, these data suggest that at least some of the increases in sodium intake over time may be due to increases in the amount of sodium in foods. Changes in intake over time must be cautiously interpreted because of limitations in these data, particularly older data based on different methodologies. However, compared to a sodium intake density of < 1,150 mg/1,000 calories per day to be consistent with a Dietary Guidelines for Americans daily intake of < 2,300 mg sodium and assuming a 2,000-calorie reference diet, most groups had intakes that exceeded guideline levels, even during the earlier periods when sodium densities appeared lower than in more recent years.
As described in Chapter 5, mean urinary sodium excretion collected over a 24-hour period is generally considered to be the gold standard for accurately estimating the sodium intake of individuals. However, in the absence of such data from nationally representative surveys in the United States, the best source of data on urinary sodium excretion of Americans is carefully designed and monitored research studies. Results for U.S. adults participating in two observational studies and four clinical trials between 1980 and the late 1990s indicate that the median urinary sodium excretion per 24 hours across all studies was approximately 3,700 mg/d for men and 3,000 mg/d for women (Loria et al., 2001). Based on the average sodium excretion across all studies, all but one group had sodium excretions of more than 2,300 mg. Eleven of 12 groups of men had average sodium excretion levels greater than 3,000 mg/d, with 4 of these groups having a mean excretion greater than 4,000 mg/d. For women, 6 of 12 groups had sodium excretions between 2,500 and 3,000 mg/d; 6 of the 12 groups had sodium excretions between 3,000 and 3,612 mg/d. Thus, the sodium excretion of U.S. adults participating in research studies showed that almost all of the groups had mean sodium excretion levels well in excess of the