Abstract:

This study aimed to identify sociodemographic factors associated with high estimated sodium/potassium ratio. A total of 15,105 participants were assessed, from 35 to 74 years of age, from a cohort of public employees (ELSA-Brazil). Socioeconomic data were collected with a questionnaire, and 12-hour nighttime urine samples were collected to estimate sodium and potassium intake. Sodium/potassium ratio was calculated in mmol/L and divided into tertiles: 1^st tertile, corresponding to “low”; 2^nd tertile for “medium”; and 3^rd tertile for “high” sodium/potassium ratio. The proportions and means were compared according to the classification of tertiles in the sodium/potassium ratio, using chi-square test and analysis of variance (ANOVA). Crude and adjusted multinomial logistic regression models were tested, with the 1st tertile as the reference. Factors associated with sodium/potassium ratio were: male sex (OR = 1.78; 95%CI: 1.60-1.98); age 35 to 44 years (OR = 1.71; 95%CI: 1.33-2.19); incomplete elementary schooling (OR = 2.38; 95%CI: 1.78-3.18); and lower income (OR = 1.47; 95%CI: 1.26-1.73). Men, younger individuals, and those with less schooling and income showed higher mean sodium/potassium ratio.

Keywords:
Sodium; Potassium; Urine

Introduction

Sodium and potassium intake is an important predictor of morbidity and mortality, and the ratio between them has proven an even better predictor of risk of hypertension and cardiovascular diseases; the ratio is considered more important than the single estimates of these two nutrients ¹1. Yang Q, Liu T, Kuklina EV, Flanders WD, Hong Y, Gillespie C, et al. Sodium and potassium intake and mortality among US adults. Arch Intern Med 2011; 171:1183-91.^,22. Bailey RL, Parker EA, Rhodes DG, Goldman JD, Clemens JC, Moshfegh AJ, et al. Estimating sodium and potassium intakes and their ratio in the American diet: data from the 2011-2012 NHANES. J Nutr 2016; 146:745-50.^,33. Okayama A, Okuda N, Miura K, Okamura T, Hayakawa T, Akasaka H, et al. Dietary sodium-to-potassium ratio as a risk factor for stroke, cardiovascular disease and all-cause mortality in Japan: the NIPPON DATA80 cohort study. BMJ Open 2016; 6:e011632.. The single estimates allow assessing excessive salt intake and inadequate consumption of fruits and vegetables, which are high in potassium. The World Health Organization (WHO) ⁴4. World Health Organization. Diet, nutrition and the prevention of chronic diseases. Geneva: World Health Organization; 2003. recommends a sodium-to-potassium ratio of 1. An increase in this ratio can be due to either elevated sodium from industrialized foods and added table salt and/or decreased potassium intake, as in a diet with low nutritional quality ⁵5. Molina MCB, Cunha RS, Herkenhoff LF, Mill JG. Hipertensão arterial e consumo de sal em população urbana. Rev Saúde Pública 2003; 37:743-50.^,66. Cordain L, Eaton SB, Sebastian A, Mann N, Lindeberg S, Watkins BA, et al. Origins and evolution of the Western diet: health implications for the 21st century. Am J Clin Nutr 2005; 81:341-54..

Studying the relationship between food consumption and health outcomes is fundamentally important for a better understanding of their determinants, as well as for planning preventive and health promotion measures. Meanwhile, the assessment of food consumption in population-based studies can be done with different methods, including dietary methods, which are feasible and less expensive, but which are less precise and prone to recall bias and error in estimating the size of portions ⁷7. Beaton GH. Approaches to analysis of dietary data: relationship between planned analyses and choice of methodology. Am J Clin Nutr 1994; 59(1 Suppl):253S-61S.. On the other hand, biomarkers are independent of random errors in relation to the inherent errors of dietary surveys, besides presenting higher precision ⁸8. Bingham SA. Biomarkers in nutritional epidemiology. Public Health Nutr 2002; 5:821-7.. In the case of sodium and potassium intake, urinary excretion provides a more precise estimate than dietary methods ⁹9. Pereira TSS, Cade NV, Mill JG, Sichieri R, Molina MCB. Use of the method of triads in the validation of sodium and potassium intake in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). PLoS One 2016; 11:e0169085., and the ratio between them is also more precise for identifying diet with lower sodium and higher potassium intake ¹⁰10. Iwahori T, Miura K, Ueshima H. Time to consider use of the sodium-to-potassium ratio for practical sodium reduction and potassium increase. Nutrients 2017; 9:E700..

Diet is influenced by various factors (economic, social, and cultural) and even some health conditions ¹¹11. Kelly S, Martin S, Kuhn I, Cowan A, Brayne C, Lafortune L. Barriers and facilitators to the uptake and maintenance of healthy behaviours by people at mid-life: a rapid systematic review. PLoS One 2016; 11:e0145074.. These factors intervene directly in access to foods and the diet’s nutritional quality. Evidence has shown that higher income, more schooling, and a favorable environment increase access to healthy foods ¹²12. Irala-Estévez J, Groth M, Johansson L, Oltersdorf U, Prättälä R, Martínez-González MA. A systematic review of socio-economic differences in food habits in Europe: consumption of fruit and vegetables. Eur J Clin Nutr 2000; 54:706-14.^,1313. Pessoa MC, Mendes LL, Gomes CS, Martins PA, Velasquez-Melendez G. Food environment and fruit and vegetable intake in a urban population: a multilevel analysis. BMC Public Health 2015; 15:1012.. Meanwhile, the presence of certain diseases interferes in food intake, whether related to inherent difficulties in the disease process or due to dietary restrictions as part of a food plan or specific diet therapy ¹⁴14. Jomori MM, Proença RPC, Calvo MCM. Determinantes de escolha alimentar. Rev Nutr 2008; 21:63-73.. Considering that sodium/potassium ratio can be used as a good marker of intake of these electrolytes, the current study aims to identify sociodemographic factors associated with high sodium/potassium ratio in adults.

Methods

Study design and population

This cross-sectional study used baseline data from the Brazilian Longitudinal Study of Adult Health (ELSA-Brazil), a multicenter study of active and retired public employees 35 to 74 years of age, whose central focus is the incidence of chronic diseases and their risk factors, particularly cardiovascular diseases and diabetes ¹⁵15. Aquino EM, Barreto SM, Bensenor IM, Carvalho MS, Chor D, Duncan B, et al. Brazilian Longitudinal Study of Adult health (ELSA-Brasil): objectives and design. Am J Epidemiol 2012; 175:315-24.. ELSA-Brazil is being conducted in six state capitals in three of Brazil’s five major geographic regions (South, Southeast, and Northeast), with six research centers, five in public universities [Federal University of São Paulo (USP), São Paulo State; Federal University of Minas Gerais (UFMG), Minas Gerais State; Federal University of Bahia (UFBA), Bahia State; Federal University of Rio Grande do Sul (UFRGS), Rio Grande do Sul State; and Federal University of Espírito Santo (UFES), Espírito Santo State] and one research institution under the Brazilian Ministry of Health (Oswaldo Cruz Foundation - Fiocruz, Rio de Janeiro State). ELSA-Brazil was approved by the institutional review boards of the six institutions, and all the participants signed the Informed Consent Form.

Exclusion criteria

The study excluded individuals that did not provide validated urine samples and those in use of any class of antihypertensive medication, since diuretics have reported natriuretic effects with the decreased extracellular volume, thus presenting altered potassium excretion (hypopotassemia) ¹⁶16. Malachias MVB, Plavnik FL, Machado CA, Malta D, Scala LCN, Fuchs S. 7ª Diretriz Brasileira de Hipertensão Arterial. Capítulo 1 - conceituação, epidemiologia e prevenção primária. Arq Bras Cardiol 2016; 107(3 Suppl 3):1-6..

Data collection

The tests and questionnaires were performed from 2008 to 2010 in standardized fashion in the six study centers, as published previously in full detail ¹⁵15. Aquino EM, Barreto SM, Bensenor IM, Carvalho MS, Chor D, Duncan B, et al. Brazilian Longitudinal Study of Adult health (ELSA-Brasil): objectives and design. Am J Epidemiol 2012; 175:315-24.^,1717. Mill JG, Pinto K, Griep RH, Goulart A, Foppa M, Lotufo PA, et al. Aferições e exames clínicos realizados nos participantes do ELSA-Brasil. Rev Saúde Pública 2013; 47:54-62..

12-hour sodium and potassium excretion

ELSA-Brazil adopted 12-hour nighttime urine collection to estimate sodium and potassium excretion and assess creatinine clearance ¹⁵15. Aquino EM, Barreto SM, Bensenor IM, Carvalho MS, Chor D, Duncan B, et al. Brazilian Longitudinal Study of Adult health (ELSA-Brasil): objectives and design. Am J Epidemiol 2012; 175:315-24.. Participants received verbal and written instructions from trained and certified personnel on the samples’ collection, storage, and transportation. Urinary volume was measured with a graduated cylinder with a capacity of 1,000mL and precision to 10mL. Sodium and potassium titrations were performed with selective electrodes. Urinary samples were defined as collection period from 10 to 14 hours, diuresis greater than 250mL, and no report of complete losses of micturition. Urine samples were considered valid when total weight-corrected creatinine excretion adjusted for 12 hours was between 7.2 and 16.8mg/kg in men and 5.4 and 12.6mg/kg in women ¹⁸18. Ljungman S, Granerus G. The evaluation of kidney function in hypertensive patients. In: Laragh JH, Brenner BM, editors. Hypertension: pathophysiology, diagnosis, and management. 2nd Ed. New York: Raven Press Limited; 1995. p. 1987-2004..

The study used 12-hour nighttime urinary sodium and potassium excretion and estimated 24-hour sodium and potassium intake in milligrams. 12-hour urinary excretion can be used in epidemiological studies because it estimates 24-hour consumption/excretion with reliable precision ¹⁹19. Mill JG, Silva ABT, Baldo MP, Molina MCB, Rodrigues SL. Correlation between sodium and potassium excretion in 24- and 12-h urine samples. Braz J Med Biol Res 2012; 45:799-805.. Sodium/potassium ratio was calculated in mmol/mmol and later divided into tertiles, classified as 1^st tertile = low, 2^nd tertile = medium, and 3^rd tertile = high.

Exploratory variables

Individuals of both sexes were evaluated. Age was classified in four brackets, namely 35 to 44, 45 to 54, 55 to 64, and 65 to 74 years. Schooling was grouped in incomplete and complete elementary, complete secondary, and complete university. Per capita income was based on information on approximate net family income in the month prior to the interview and the number of persons that depended on it. This variable was divided into tertiles, where the first tertile indicates the lowest income and the last tertile the highest income. Race/color was self-reported and grouped into white and non-white (black, brown, Asian-descendant, and indigenous).

Statistical analysis

Descriptive analysis of the sociodemographic variables was performed according to tertiles of sodium/potassium ratio using the chi-square test. Mean values for sodium, potassium, and sodium/potassium ratio were compared using analysis of variance (ANOVA) followed by Tukey post hoc and Student’s t-test. Crude and adjusted multinomial logistic regression model was tested, where the dependent variable was sodium/potassium ratio in tertiles and the reference was low ratio (1^st tertile). The independent variables used in the model were sex, age bracket, schooling, race/color, and income. The data were analyzed with the SPSS version 18.0 (https://www.ibm.com/).

Results

Of the 15,105 participants, 2,292 individuals were excluded because they failed to provide validated urine collection and 3,734 were excluded because they reported use of antihypertensive medication, thus constituting a final sample of 9,079 individuals.

Individuals with high sodium/potassium ratio presented the highest mean sodium and lowest potassium (Table 1). High mean sodium/potassium ratio was associated with male sex, younger age (35 to 44 years), lower schooling, non-white ethnicity, and lower income (Table 2).

Estimated sodium and potassium intake showed a significant difference between sex and schooling (Table 3). Higher mean sodium/potassium ratios were observed in men, younger individuals, and individuals with lower schooling and income (Table 3). Table 4 shows the crude and adjusted multinomial logistic regression models. In the adjusted model, men showed 78% higher odds of high sodium/potassium ratio when compared to women. Younger individuals (35 to 44 years: OR = 1.71; 95%CI: 1.33-2.19) and those with lower schooling (OR = 2.38; 95%CI: 1.78-3.18) and income (OR = 1.47; 95%CI: 1.26-1.73) showed higher odds of high sodium/potassium ratio.

Discussion

Factors associated with high sodium/potassium ratio were male sex, younger age, and lower schooling and income. These characteristics were associated with higher odds of consuming a high-sodium and low-potassium diet. Elevated sodium/potassium ratio is due to consumption of high-sodium foods such as processed and ultra-processed products and the addition of table salt and industrialized seasonings when preparing meals ²⁰20. Louzada MLC, Martins APB, Canella DS, Baraldi LG, Levy RB, Claro RM, et al. Ultra-processed foods and the nutritional dietary profile in Brazil. Rev Saúde Pública 2015; 49:38.. Meanwhile, lower ratio indicates higher consumption of fruits and vegetables, considered important sources of potassium ²¹21. Weaver CM. Potassium and health. Adv Nutr 2013; 4:368S-77S..

In this study, women showed lower mean sodium/potassium ratio than men. This may mean that women were more concerned about their health ²²22. Deeks A, Lombard C, Michelmore J, Teede H. The effects of gender and age on health related behaviors. BMC Public Health 2009; 9:213. and thus probably ate a better diet, including daily fruits and vegetables. Assumpção et al. ²³23. Assumpção D, Domene SMA, Fisberg RM, Canesqui AM, Barros MBA. Diferenças entre homens e mulheres na qualidade da dieta: estudo de base populacional em Campinas, São Paulo. Ciênc Saúde Colet 2017; 22:347-58. found that women eat more fruits and vegetables when compared to men. The same result appeared in the Brazilian National Health Survey²⁴24. Malta DC, Andrade SSCA, Stopa SR, Pereira CS, Szwarcwald CL, Silva Júnior JB, et al. Estilos de vida da população brasileira: resultados da Pesquisa Nacional de Saúde, 2013. Epidemiol Serv Saúde 2015; 24:217-26..

Another issue is changes with aging, since older individuals may be more aware of their own health care, as demonstrated by Deeks et al. ²²22. Deeks A, Lombard C, Michelmore J, Teede H. The effects of gender and age on health related behaviors. BMC Public Health 2009; 9:213.. However, we noted that older participants presented lower sodium/potassium ratio, probably due to higher consumption of fruits and vegetables. Younger individuals tend to eat away from home more often, frequently replacing full meals with quick snacks like fast foods, contributing to worse diet ²⁵25. Bezerra IN, Souza AM, Pereira RA, Sichieri R. Consumo de alimentos fora do domicílio no Brasil. Rev Saúde Pública 2013;47 Suppl 1:200S-11S..

Information on the benefits of healthy eating with lower amounts of sodium and processed foods is currently available to the entire population, but real access to this type of diet can be limited to individuals with more schooling. Better knowledge on the benefits of adequate or more nutritious diet assists eating choices. Data from the VIGITEL survey (Risk and Protective Factors Surveillance System for Chronic Non-communicable Diseases through Telephone Interview) ²⁶26. Departamento de Vigilância de Doenças e Agravos não Transmissíveis e Promoção da Saúde, Secretaria de Vigilância em Saúde, Ministério da Saúde. VIGITEL Brasil 2016: Vigilância de Fatores de Risco e Proteção para Doenças Crônicas por Inquérito Telefônico. Brasília: Ministério da Saúde; 2017. show that 44.3% of Brazilian adults with 12 or more years of schooling report consuming fruits and vegetables five or more days a week, while those with fewer than nine years of schooling consumed 29.9%.

Income is also a determinant factor for food choices. Faleiro et al. ²⁷27. Faleiro JC, Giatti L, Barreto SM, Camelo LV, Griep RH, Guimarães JMN, et al. Posição socioeconômica no curso de vida e comportamentos de risco relacionados à saúde: ELSA-Brasil. Cad Saúde Pública 2017; 33:e00017916. demonstrated that lower socioeconomic status was associated with higher prevalence of low consumption of fruits and vegetables. Healthy foods tend to be costlier than industrialized foods ²⁸28. Claro RM, Maia EG, Costa BVL, Diniz DP. Preço dos alimentos no Brasil: prefira preparações culinárias a alimentos ultraprocessados. Cad Saúde Pública 2016; 32:e00104715., which is one factor favoring choice of the latter for people with less buying power ¹²12. Irala-Estévez J, Groth M, Johansson L, Oltersdorf U, Prättälä R, Martínez-González MA. A systematic review of socio-economic differences in food habits in Europe: consumption of fruit and vegetables. Eur J Clin Nutr 2000; 54:706-14.. Although less costly and more practical, industrialized foods are high in calories, fat, salt, and sugar ²⁰20. Louzada MLC, Martins APB, Canella DS, Baraldi LG, Levy RB, Claro RM, et al. Ultra-processed foods and the nutritional dietary profile in Brazil. Rev Saúde Pública 2015; 49:38.. A study by Simões et al. ²⁹29. Simões BS, Cardoso LO, Benseñor IJM, Schmidt MI, Duncan BB, Luft VC, et al. Consumption of ultra-processed foods and socioeconomic position: a cross-sectional analysis of the Brazilian Longitudinal Study of Adult Health. Cad Saúde Pública 2018; 34:e00019717., with participants in ELSA-Brazil, showed that the highest share of energy density came from ultra-processed foods, among individuals with less schooling. The race/color variable did not remain in the final model. Although participants in ELSA-Brazil are public employees with higher income and schooling than the Brazilian national average, the sodium/potassium ratio was higher than in the U.S. population ²2. Bailey RL, Parker EA, Rhodes DG, Goldman JD, Clemens JC, Moshfegh AJ, et al. Estimating sodium and potassium intakes and their ratio in the American diet: data from the 2011-2012 NHANES. J Nutr 2016; 146:745-50..

Urinary excretion is a gold standard for estimating sodium and potassium intake ⁹9. Pereira TSS, Cade NV, Mill JG, Sichieri R, Molina MCB. Use of the method of triads in the validation of sodium and potassium intake in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). PLoS One 2016; 11:e0169085.. Thus, sodium/potassium ratio can be used as a marker of intake of these electrolytes, since it lacks the biases found in dietary methods. Still, this indicator is not able to identify the foods consumed by the population, which is considered a limitation. However, Oliveira et al. ³⁰30. Oliveira LS, Coelho JS, Siqueira JH, Santana NMT, Pereira TSS, Molina MCB. Relación sodio/potasio urinario y consumo de condimentos industrializados y alimentos ultraprocesados. Nutr Hosp 2019; 36:125-32. found that frequent consumption of industrialized seasonings is associated with the highest urinary sodium excretion and sodium/potassium ratio. Higher consumption of ultra-processed foods has also been associated with higher sodium/potassium ratio ³⁰30. Oliveira LS, Coelho JS, Siqueira JH, Santana NMT, Pereira TSS, Molina MCB. Relación sodio/potasio urinario y consumo de condimentos industrializados y alimentos ultraprocesados. Nutr Hosp 2019; 36:125-32.. Thus, the higher the sodium/potassium ratio, the higher the sodium intake and the lower the potassium intake.

Although sodium is widely distributed in small amounts in whole foods, its principal source in contemporary diet is table salt. Foods with the highest amounts of sodium include cold cuts, cookies, and readymade meals and seasonings, among others. Since this nutrient is present in the foods that are part of current global food variety, one can predict that individuals will tend to consume much more sodium than recommended, potentially increasing the sodium/potassium ratio. The addition of salt to readymade meals is also more common in men than in women ³¹31. Castro RSA, Giatti L, Barreto SM. Fatores associados à adição de sal a refeição pronta. Ciênc Saúde Colet 2014; 10:1503-12..

Therefore, even though urinary sodium/potassium ratio does not allow identifying food sources or the precise sources increasing the ratio, one can state that higher ratios are associated with greater consumption of industrialized seasonings and processed foods ³⁰30. Oliveira LS, Coelho JS, Siqueira JH, Santana NMT, Pereira TSS, Molina MCB. Relación sodio/potasio urinario y consumo de condimentos industrializados y alimentos ultraprocesados. Nutr Hosp 2019; 36:125-32.. Thus, the study’s results corroborate the fact that demographic and socioeconomic factors are important determinants of food choices ²³23. Assumpção D, Domene SMA, Fisberg RM, Canesqui AM, Barros MBA. Diferenças entre homens e mulheres na qualidade da dieta: estudo de base populacional em Campinas, São Paulo. Ciênc Saúde Colet 2017; 22:347-58.^,3232. Sichieri R, Castro JFG, Moura AS. Fatores associados ao padrão de consumo alimentar da população brasileira urbana. Cad Saúde Pública 2003; 19 Suppl 1:S47-53., and that sodium/potassium ratio can be used as a summary indicator of diet quality, contributing to monitoring of policies to promote healthy eating.

Conclusion

High sodium/potassium ratio was found in males, young individuals, and those with lower schooling and lower income. In addition, individuals in the first tertile of the sodium/potassium ratio showed higher levels than recommended.

Acknowledgments

The authors wish to thank the team and participants of the ELSA-Brazil study for their important contributions, as well as the Brazilian Ministry of Health, Innovation and Research Funding and Brazilian National Research Council (CNPq), for the financial support.

References

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History