Association between socioeconomic factors and urinary sodium-to-potassium ratio: the Nagahama Study


High sodium intake is a simple modifiable risk factor for hypertension. Although not confirmed, lower socioeconomic status may be a factor that increases sodium intake. We aimed to clarify the association between socioeconomic status and urinary sodium-to-potassium ratio by cross-sectional and longitudinal analyses. The study included 9410 community residents. Spot urine sodium-to-potassium ratios were measured twice with a 5-year interval. Socioeconomic status was investigated using a self-administered questionnaire. Cross-sectional analysis revealed that educational attainment was inversely associated with urinary sodium-to-potassium ratio (years of education ≤ 9: 3.0 ± 1.8, ≤ 12: 2.9 ± 1.6, ≥ 13: 2.8 ± 1.6; P < 0.001), whereas no significant association was observed with household income. Men, particularly individuals living alone, exhibited markedly high sodium-to-potassium ratios (3.6 ± 2.3). Although frequent intake of vegetables, fruits, and dairy products was also inversely associated with the ratio, the associations with educational attainment ( ≤ 9: reference, ≤ 12: β = −0.032, P = 0.026, ≥ 13: β= −0.059, P < 0.001), marital status (β = −0.040, P < 0.001), and sex*marital status interaction (β = 0.054, P = 0.001) were independent of these covariates. Educational attainment was also inversely associated with differences in the urinary sodium-to-potassium ratio during the follow-up period (odds ratio, 0.70; P < 0.001). Lower educational attainment was an independent determinant for urinary sodium-to-potassium ratio. Health literacy education, particularly in men living alone, may be a factor for reducing salt intake even in high-income countries where equal educational opportunity is assured.

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  1. 1.

    Intersalt Cooperative Research Group. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 h urinary sodium and potassium excretion. BMJ. 1988;297:319–28.

  2. 2.

    Tabara Y, Takahashi Y, Kumagai K, Setoh K, Kawaguchi T, Takahashi M, et al. Descriptive epidemiology of spot urine sodium-to-potassium ratio clarified close relationship with blood pressure level: the Nagahama study. J Hypertens. 2015;33:2407–13.

  3. 3.

    Han W, Han X, Sun N, Chen Y, Jiang S, Li M. Relationships between urinary electrolytes excretion and central hemodynamics, and arterial stiffness in hypertensive patients. Hypertens Res. 2017;40:746–51.

  4. 4.

    Mente A, O’Donnell MJ, Rangarajan S, McQueen MJ, Poirier P, Wielgosz A, et al. Association of urinary sodium and potassium excretion with blood pressure. N Engl J Med. 2014;371:601–11.

  5. 5.

    Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, et al. Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. N Engl J Med. 2001;344:3–10.

  6. 6.

    He FJ, Li J, Macgregor GA. Effect of longer term modest salt reduction on blood pressure: cochrane systematic review and meta-analysis of randomized trials. BMJ. 2013;346:f1325.

  7. 7.

    O’Donnell MJ, Yusuf S, Mente A, Gao P, Mann JF, Teo K, et al. Urinary sodium and potassium excretion and risk of cardiovascular events. JAMA. 2011;306:2229–38.

  8. 8.

    O’Donnell M, Mente A, Rangarajan S, McQueen MJ, Wang X, Liu L, et al. Urinary sodium and potassium excretion, mortality, and cardiovascular events. N Engl J Med. 2014;371:612–23.

  9. 9.

    de Mestral C, Mayén AL, Petrovic D, Marques-Vidal P, Bochud M, Stringhini S. Socioeconomic determinants of sodium intake in adult populations of high-income countries: a systematic review and meta-analysis. Am J Public Health. 2017;107:e1–e12.

  10. 10.

    Hong JW, Noh JH, Kim DJ. Factors associated with high sodium intake based on estimated 24-hour urinary sodium excretion: the 2009–11 Korea national health and nutrition examination survey. Medicine. 2016;95:e2864.

  11. 11.

    Chien KL, Hsu HC, Chen PC, Su TC, Chang WT, Chen MF, et al. Urinary sodium and potassium excretion and risk of hypertension in Chinese: report from a community-based cohort study in Taiwan. J Hypertens. 2008;26:1750–6.

  12. 12.

    Miyaki K, Song Y, Taneichi S, Tsutsumi A, Hashimoto H, Kawakami N, et al. Socioeconomic status is significantly associated with dietary salt intakes and blood pressure in Japanese workers (J-HOPE Study). Int J Environ Res Public Health. 2013;10:980–93.

  13. 13.

    Uechi K, Asakura K, Masayasu S, Sasaki S. Within-country variation of salt intake assessed via urinary excretion in Japan: a multilevel analysis in all 47 prefectures. Hypertens Res. 2017;40:598–605.

  14. 14.

    Brown IJ, Tzoulaki I, Candeias V, Elliott P. Salt intakes around the world: implications for public health. Int J Epidemiol. 2009;38:791–813.

  15. 15.

    Ji C, Cappuccio FP. Socioeconomic inequality in salt intake in Britain 10 years after a national salt reduction programme. BMJ Open. 2014;4:e005683.

  16. 16.

    Morris RC Jr, Sebastian A, Forman A, Tanaka M, Schmidlin O. Normotensive salt sensitivity: effects of race and dietary potassium. Hypertension. 1999;33:18–23.

  17. 17.

    Adrogué HJ, Madias NE. Sodium and potassium in the pathogenesis of hypertension. N Engl J Med. 2007;356:1966–78.

  18. 18.

    Kawasaki T, Itoh K, Uezono K, Sasaki H. A simple method for estimating 24 h urinary sodium and potassium excretion from second morning voiding urine specimen in adults. Clin Exp Pharmacol Physiol. 1993;20:7–14.

  19. 19.

    Tanaka T, Okamura T, Miura K, Kadowaki T, Ueshima H, Nakagawa H, et al. A simple method to estimate populational 24-h urinary sodium and potassium excretion using a casual urine specimen. J Hum Hypertens. 2002;16:97–103.

  20. 20.

    Jayaweera S. Gender and access to education in Asia. Int Rev Educ. 1987;33:455–66.

  21. 21.

    Matsuo S, Imai E, Horio M, Yasuda Y, Tomita K, Nitta K, et al. Revised equations for estimated GFR from serum creatinine in Japan. Am J Kidney Dis. 2009;53:982–92.

  22. 22.

    Taylor EN, Stampfer MJ, Mount DB, Curhan GC. DASH-style diet and 24-hour urine composition. Clin J Am Soc Nephrol. 2010;5:2315–22.

  23. 23.

    Cappuccio FP, Ji C, Donfrancesco C, Palmieri L, Ippolito R, Vanuzzo D, et al. Geographic and socioeconomic variation of sodium and potassium intake in Italy: results from the MINISAL-GIRCSI programme. BMJ Open. 2015;5:e007467.

  24. 24.

    Ji C, Kandala NB, Cappuccio FP. Spatial variation of salt intake in Britain and association with socioeconomic status. BMJ Open. 2013;3:e002246.

  25. 25.

    Tani Y, Kondo N, Takagi D, Saito M, Hikichi H, Ojima T, et al. Combined effects of eating alone and living alone on unhealthy dietary behaviors, obesity and underweight in older Japanese adults: results of the JAGES. Appetite. 2015;95:1–8.

  26. 26.

    Si Hassen W, Castetbon K, Cardon P, Enaux C, Nicolaou M, Lien N, et al. Socioeconomic indicators are independently associated with nutrient intake in French adults: a DEDIPAC study. Nutrients. 2016;8:158.

  27. 27.

    Iwahori T, Ueshima H, Torii S, Saito Y, Kondo K, Tanaka-Mizuno S, et al. Diurnal variation of urinary sodium-to-potassium ratio in free-living Japanese individuals. Hypertens Res. 2017;40:658–64.

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We are extremely grateful to the Nagahama City Office and the nonprofit organization Zeroji Club for their support in performing the Nagahama Study. The authors would like to thank Enago ( for the English language review.


The study was supported by a university grant, The Center of Innovation Program, The Global University Project, and a Grant-in-Aid for Scientific Research (25293141, 26670313) from the Ministry of Education, Culture, Sports, Science & Technology in Japan, the Practical Research Project for Rare/Intractable Diseases (ek0109070, ek0109196), the Comprehensive Research on Aging and Health Science Research Grants for Dementia R&D (dk0207006), the Program for an Integrated Database of Clinical and Genomic Information (kk0205008) from Japan Agency for Medical Research and Development (AMED), and the Takeda Medical Research Foundation.

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Correspondence to Yasuharu Tabara.

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  • Salt intake
  • Sodium-to-potassium ratio
  • Educational attainment
  • Socioeconomic status
  • General population

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