Among adults with hypertension, studies have shown that a reduction in sodium intake is significantly associated with lowering of blood pressure. In a 2010 report on strategies to reduce sodium intake, the Institute of Medicine (IOM; now the National Academy of Medicine), said, “A more accurate measure of total sodium intake such as 24-hour urine collection should be employed in national population surveys, specifically NHANES (the National Health and Nutrition Examination Survey).” That recommendation was based on a review of studies indicating that 24-hour urinary excretion, when complete, reflects approximately 90% of sodium consumed from all sources.
Blood pressure is also associated with potassium intake, which is linked with sodium in biology and physiology. In addition, potassium chloride is used as a substitute for salt, making current estimation of 24-hour urinary potassium excreted efficient, even though the amount of potassium excreted in 24-hour urine collection in previous studies was variable (50% to 90%).
Mary E. Cogswell, DrPH, and colleagues recently conducted a study designed to estimate mean sodium intake among adults in the United States from 24-hour urinary excretion. Secondary objectives included estimates of mean 24-hour urinary potassium excretion and the sodium-to-potassium molar ratio. Results of the study were reported online in JAMA [doi:10.1001/jama.2018.1156].
There were 4656 nonpregnant adults 20 to 69 years of age who participated in the examination component of the 2013-2014 NHANES; of those, 2228 participated in 2014. Among the 2228 participating in 2014, 1103 were randomly selected and asked to participate in 24-hour urine collection post-examination. Of those 1103, 827 completed an initial 24-hour urine collection (421 men and 406 women).
There were differences in completion rates based on sex, race and Hispanic origin, education, body mass index (BMI), and hypertension status. With the exception of non-Hispanic Asians and those with a BMI <25.0, completion was >70% across subgroups. The overall survey response rate for the 24-hour urine collection was an estimated 50% (75% [24-hour urine completion rate] ´ 66% [NHANES examination response rate]).
Of the total NHANES 2013-2014 examination component cohort (n=4656), there were no statistically significant differences in demographic characteristics or cardiovascular disease risk factors between those who completed the 2014 24-hour urine collection and those who did not.
Among the 827 who completed the 24-hour urine collection, 48.8% were men, 63.7% were non-Hispanic white, 15.8% were Hispanic, 11.9% were non-Hispanic black, and 5.6% were non-Hispanic Asian. Based on 2017 hypertension guidelines, 43.5% had hypertension; 10.0% reported a diagnosis of diabetes. A higher percentage of men than women were estimated to have hypertension (47.6% vs 37.9%; P=.03).
Of 585 participants selected, 436 completed a second 24-hour urine collection (53% of the 827 who completed the first collection; men, 255; women, 211). There were no significant variations in population characteristics, mean initial 24-hour urine volume, and mean urinary electrolyte and creatinine excretion when estimated based on participants who collected one versus two complete 24-hour urine specimens.
Overall weighted mean 24-hour urinary sodium excretion was 3608 mg (95% confidence interval [CI], 3414-3803). The median 24-hour urinary sodium excretion was 3320 mg. In secondary analyses by sex, mean 24-hour urinary sodium excretion was 4205 mg (95% CI, 3959-4452) in men and 3039 mg (95% CI, 2844-3234) in women (between-group P<.001). Sodium excretion by age group was 3699 mg (95% CI, 3449-3949) in those 20 to 44 years of age (n=432) and 3507 mg (95% CI, 3266-3748) in those 45 to 69 years of age (n=395).
Results of exploratory analyses suggested that mean 24-hour urinary sodium excretion was generally higher for adults 20 to 59 years of age compared with adults 60 to 69 years of age. There also appeared to be significant variations in mean 24-hour urinary sodium by BMI, hypertension status, and diabetes status.
The proportion of adults with 24-hour urinary sodium excretion ≥2300 mg on any given day was 75.1% (95% CI, 72.0%-78.2%) overall (n=827), 83.5% (95% CI, 79.9%-87.0%) in men (n=421), and 67.1% (95% CI, 62.1%-72.05) in women (n=406).
Weighted overall mean 24-hour urinary potassium excretion was 2155 mg (95% CI, 2030-2280); the median was 2000 mg. In secondary analyses, among men, the mean 24-hour urinary potassium excretion was 2399 mg (95% CI, 2253-2545); among women, 1922 mg (95% CI, 1757-2086), P<.001. There was variation by age: mean 24-hour urinary potassium excretion was lower among participants 45 to 69 years of age compared with those 20 to 44 years of age. There were also variations in exploratory analyses in mean 24-hour urinary potassium excretion between groups defined by race and Hispanic origin, income level, education, and BMI (in men).
The overall mean sodium-to-potassium molar ratio was 3.17 (95% CI, 2.91-3.43); median was 2.87. In secondary analyses, the mean sodium-to-potassium molar ratio was similar by sex. In overall and in sex subgroups, the molar ratio was higher among participants 20 to 44 years of age compared with those 45 to 69 years of age.
The researchers cited several limitations to the study including the inability to account for all potential sources of bias despite electrolyte estimates being weighted to account for sampling and nonresponse. In addition, the generalizability of the results may be limited, particularly among subgroups with low response rates (non-Hispanic Asians). Finally, incomplete collection of 24-hour urine might have resulted in lower estimated sodium and potassium excretion.
In conclusion, the researchers said, “In cross-sectional data from a 2014 sample of US adults, estimated mean sodium intake was 3608 mg per day. The findings provide a benchmark for future studies.”
- Researchers utilized data from a nationally representative cross-sectional survey to estimate mean population sodium intake and describe urinary potassium excretion among adults in the United States.
- Overall weighted mean 24-hour urinary sodium excretion was 3608 mg; 4205 mg in men and 3039 mg in women. In secondary analyses, there were variations by body mass index, hypertension status, and diabetes status.
- Weighted mean 24-hour urinary potassium excretion was 2155 mg overall; 2399 mg in men and 1922 mg in women.