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of water samples from local municipal sources, finding a mean sodium concentration of 278 mg/L (similar to the mean of 269 mg/L reported in other literature) with a range of 172–1,219 mg/L. Municipal water averaged 110 mg sodium per liter, with a range of 0–253 mg/L. The authors concluded that an average daily consumption of 2.5 liters of water could provide up to an average of 695 mg sodium, or up to 3,047 mg sodium from the water with the highest concentrations. A report from the Mayo Clinic suggests that, in general, an 8-ounce glass of softened tap water contains around 12 mg of sodium.12

Dietary Supplements

On average, the intake of sodium due to use of dietary supplements is very low (i.e., less than 1 percent of total sodium intake in NHANES 2003–2006) (see Table 5-1 and Appendix F, Table F-1). However, although these estimates are low on a population basis, supplements can be a meaningful source of sodium for some individuals. For example, in NHANES 2003–2006, the estimated daily contribution from supplements ranged from 0.02 to 540 mg13 among supplement users.

Measures Based on Urine Analysis

Although estimates of sodium intake based on 24-hour dietary recall methods provide important and useful estimates of intake, they likely underestimate the true total intake of sodium in the population. Mean urinary sodium excretion over a 24-hour period is generally considered to be the gold standard for accurately estimating the sodium intake of individuals. The main route of sodium disposal is through urine, with only small losses through perspiration and stool. Studies in which sodium intake and excretion were very carefully monitored showed that a 24-hour urinary sodium excretion captures about 90 percent or more of the ingested sodium (Clark and Mossholder, 1986; Luft et al., 1982; McCullough et al., 1991; Ovesen and Boeing, 2002; Reinivuo et al., 2006; Schachter et al., 1980).

Obtaining 24-hour urine collections from individuals is challenging (Elliott, 1989). It requires the willing participation of individuals who must carry a container to collect their urine for a full 24 hours. Less challenging collections include measuring urinary sodium excretion in “casual”

12

Available online: http://www.mayoclinic.com/health/sodium/AN00317 (accessed June 3, 2009).

13

One survey respondent reported use of a performance workout supplement containing 4,600 mg of sodium per serving dose; the next-highest reported daily amount from supplements was 540 mg.



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