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      Diurnal variation of urinary sodium-to-potassium ratio in free-living Japanese individuals

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          Abstract

          High sodium-to-potassium ratios are associated with elevated blood pressure levels and an increased risk of cardiovascular diseases. We aimed to determine whether urinary sodium-to-potassium ratios fluctuate diurnally during the day to understand measured values of casual urinary sodium-to-potassium ratios. A total of 13,277 casual urine specimens were collected under free-living conditions from 122 Japanese normotensive and hypertensive individuals. Participants collected all casual urine samples in aliquot tubes, reported urine volumes and the time at each voiding for 10–22 days. Then, specimens were classified into hourly data. Diurnal patterns of urinary sodium-to-potassium ratios and urinary concentrations of sodium and potassium were evaluated. Overall mean values of hourly urinary sodium-to-potassium ratios were highest (4.1–5.0) in the early morning, lower (3.3–3.8) in the daytime and higher (4.0–4.4) toward evening hours. The mean urinary sodium and potassium concentrations were the lowest (90–110 and 24–32 mmol l −1, respectively) during the early morning and higher (110–140 and 35–43 mmol l −1, respectively) after mid-morning. Diurnal variability of potassium concentrations was larger than for sodium concentrations. Diurnal variations in urinary sodium-to-potassium ratios were comparable between normotensive and hypertensive individuals, between hypertensive individuals with and without antihypertensive medications, and among age and gender-specific subgroups. Overall mean hourly urinary sodium-to-potassium ratios fluctuated diurnally under free-living conditions and were higher during the morning and evening and lower during the daytime compared with 24-h urinary sodium-to-potassium ratios. Diurnal variation in urinary sodium-to-potassium ratios should be considered to understand actual daily dietary levels and avoid over- and under-estimation in clinical practice.

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          Most cited references 38

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          Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Intersalt Cooperative Research Group.

          The relations between 24 hour urinary electrolyte excretion and blood pressure were studied in 10,079 men and women aged 20-59 sampled from 52 centres around the world based on a highly standardised protocol with central training of observers, a central laboratory, and extensive quality control. Relations between electrolyte excretion and blood pressure were studied in individual subjects within each centre and the results of these regression analyses pooled for all 52 centres. Relations between population median electrolyte values and population blood pressure values were also analysed across the 52 centres. Sodium excretion ranged from 0.2 mmol/24 h (Yanomamo Indians, Brazil) to 242 mmol/24 h (north China). In individual subjects (within centres) it was significantly related to blood pressure. Four centres found very low sodium excretion, low blood pressure, and little or no upward slope of blood pressure with age. Across the other 48 centres sodium was significantly related to the slope of blood pressure with age but not to median blood pressure or prevalence of high blood pressure. Potassium excretion was negatively correlated with blood pressure in individual subjects after adjustment for confounding variables. Across centres there was no consistent association. The relation of sodium to potassium ratio to blood pressure followed a pattern similar to that of sodium. Body mass index and heavy alcohol intake had strong, significant independent relations with blood pressure in individual subjects.
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            Sodium and potassium intake and mortality among US adults: prospective data from the Third National Health and Nutrition Examination Survey.

            Several epidemiologic studies suggested that higher sodium and lower potassium intakes were associated with increased risk of cardiovascular diseases (CVD). Few studies have examined joint effects of dietary sodium and potassium intake on risk of mortality. To investigate estimated usual intakes of sodium and potassium as well as their ratio in relation to risk of all-cause and CVD mortality, the Third National Health and Nutrition Examination Survey Linked Mortality File (1988-2006), a prospective cohort study of a nationally representative sample of 12,267 US adults, studied all-cause, cardiovascular, and ischemic heart (IHD) diseases mortality. During a mean follow-up period of 14.8 years, we documented a total of 2270 deaths, including 825 CVD deaths and 443 IHD deaths. After multivariable adjustment, higher sodium intake was associated with increased all-cause mortality (hazard ratio [HR], 1.20; 95% confidence interval [CI], 1.03-1.41 per 1000 mg/d), whereas higher potassium intake was associated with lower mortality risk (HR, 0.80; 95% CI, 0.67-0.94 per 1000 mg/d). For sodium-potassium ratio, the adjusted HRs comparing the highest quartile with the lowest quartile were HR, 1.46 (95% CI, 1.27-1.67) for all-cause mortality; HR, 1.46 (95% CI, 1.11-1.92) for CVD mortality; and HR, 2.15 (95% CI, 1.48-3.12) for IHD mortality. These findings did not differ significantly by sex, race/ethnicity, body mass index, hypertension status, education levels, or physical activity. Our findings suggest that a higher sodium-potassium ratio is associated with significantly increased risk of CVD and all-cause mortality, and higher sodium intake is associated with increased total mortality in the general US population.
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              Methodological issues in cohort studies that relate sodium intake to cardiovascular disease outcomes: a science advisory from the American Heart Association.

               Frank Hu,  James Neaton,   (2014)
              The results of cohort studies relating sodium (Na) intake to blood pressure-related cardiovascular disease (CVD) are inconsistent. To understand whether methodological issues account for the inconsistency, we reviewed the quality of these studies. We reviewed cohort studies that examined the association between Na and CVD. We then identified methodological issues with greatest potential to alter the direction of association (reverse causality, systematic error in Na assessment), some potential to alter the direction of association (residual confounding, inadequate follow-up), and the potential to yield false null results (random error in Na assessment, insufficient power). We included 26 studies with 31 independent analyses. Of these, 13 found direct associations between Na and CVD, 8 found inverse associations, 2 found J-shaped associations, and 8 found null associations only. On average there were 3 to 4 methodological issues per study. Issues with greater potential to alter the direction of association were present in all but 1 of the 26 studies (systematic error, 22; reverse causality, 16). Issues with lesser potential to alter the direction of association were present in 18 studies, whereas those with potential to yield false null results were present in 23. Methodological issues may account for the inconsistent findings in currently available observational studies relating Na to CVD. Until well-designed cohort studies in the general population are available, it remains appropriate to base Na guidelines on the robust body of evidence linking Na with elevated blood pressure and the few existing general population trials of the effects of Na reduction on CVD.
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                Author and article information

                Journal
                Hypertens Res
                Hypertens. Res
                Hypertension Research
                Nature Publishing Group
                0916-9636
                1348-4214
                July 2017
                26 January 2017
                : 40
                : 7
                : 658-664
                Affiliations
                [1 ]Department of Research and Development, OMRON Healthcare Co., Ltd. , Muko, Japan
                [2 ]Department of Public Health, Shiga University of Medical Science , Otsu, Japan
                [3 ]Center for Epidemiologic Research in Asia, Shiga University of Medical Science , Otsu, Japan
                [4 ]Department of Nursing, Aino University , Ibaraki, Japan
                [5 ]Department of Medical Statistics, Shiga University of Medical Science , Otsu, Japan
                [6 ]Department of Preventive Medicine and Public Health, Fukuoka University , Fukuoka, Japan
                Author notes
                [* ]Department of Public Health, Shiga University of Medical Science, Tsukinowa-cho Seta , Shiga, Otsu 520 2192, Japan. E-mail: iwahori@ 123456belle.shiga-med.ac.jp
                Article
                hr2016187
                10.1038/hr.2016.187
                5520391
                28123179
                Copyright © 2017 The Author(s)

                This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/4.0/

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