|Year : 2021 | Volume
| Issue : 4 | Page : 183-187
Methods of dietary sodium estimation
P Aparna1, Harshal Ramesh Salve1, Anand Krishnan1, Ramakrishnan Lakshmy2, Sanjeev Kumar Gupta1, Baridalyne Nongkynrih1
1 Centre for Community Medicine, All India Institute of Medical Sciences, New Delhi, India
2 Department of Cardiac Biochemistry, All India Institute of Medical Sciences, New Delhi, India
|Date of Submission||24-Aug-2021|
|Date of Acceptance||21-Sep-2021|
|Date of Web Publication||20-Oct-2021|
Dr. P Aparna
232, 20th Main, B block, 3rd Stage, Vijaynagar, Mysore - 570 030, Karnataka
Source of Support: None, Conflict of Interest: None
Excessive dietary sodium intake is found to be associated with high blood pressure and its consequences such as cardiovascular disease and stroke. Daily sodium intake is found to vary from place to place as it is dependent on geography, ethnicity, socioeconomic factors, etc. In this review, we summarize the various methods of assessment of daily sodium intake such as dietary estimation methods using 24-h dietary recall, food frequency questionnaire and diet record, and biochemical methods using 24-h urine sodium or spot urine sodium estimation. Daily sodium intake estimated with spot urine sodium is dependent on the equation used to convert spot urine sodium to 24-h urine sodium. To identify the appropriate equation, validation studies need to be conducted. Population level sodium intake and it's monitoring is important for reduction of noncommunicable diseases.
Keywords: Diet, estimation, method, salt, sodium, urine
|How to cite this article:|
Aparna P, Salve HR, Krishnan A, Lakshmy R, Gupta SK, Nongkynrih B. Methods of dietary sodium estimation. Indian J Med Spec 2021;12:183-7
|How to cite this URL:|
Aparna P, Salve HR, Krishnan A, Lakshmy R, Gupta SK, Nongkynrih B. Methods of dietary sodium estimation. Indian J Med Spec [serial online] 2021 [cited 2023 Jun 9];12:183-7. Available from: http://www.ijms.in/text.asp?2021/12/4/183/328644
| Introduction|| |
Salt or table salt is a chemical compound usually made of approximately 40% sodium and 60% chloride. Sodium and chloride are important electrolytes needed for normal physiological functioning of the human body. Approximately 90% of sodium we eat is derived from the table salt. The terms, salt and sodium, are often used interchangeably by health-care providers as the sodium portion is the one relevant for health and the estimation of one gives the estimate of the other. Sodium is involved in maintaining fluid-electrolyte balance, cell integrity, generating nerve impulses, and various other important functions. Metabolic studies have shown that sodium balance can be maintained with long term intake of 100–375 mg sodium (i.e., 0.25 g–0.9 g salt) per day. Over the ages, population-level salt intake has showed upward trend. The global mean salt intake was estimated to be 10.1 g/day (95% confidence interval [CI]: 9.9–10.2) in 2010. A systematic review done in India which included studies from 1986 to 2014 showed overall mean weighted salt intake as 10.9 g/day (95% CI: 8.6–13.4).
Scientific and medical evidence associates excessive sodium intake with high blood pressure and secondary consequences such as cardiovascular disease and stroke., The mechanisms by which dietary salt increases arterial pressure are not fully understood, but they seem related to the inability of the kidneys to excrete large amounts of salt. High salt intake is also known to cause osteoporosis, obesity, gastric cancer, and chronic kidney disease.
The World Health Organization (WHO) recommends a reduction in sodium intake to <2 g/day in adults (≥16 years). This recommendation is to reduce blood pressure and risk of cardiovascular disease and stroke.
The estimates of daily salt intake all over the world are more than the recommendation given by the WHO. Some of the countries consume more than twice the recommendation for daily salt intake.,,, As a part of the “25 by 25” initiative, the WHO set a target of 30% reduction in mean population salt consumption by 2025, which has been also endorsed by all the member nations. This initiative also includes a 25% reduction in premature mortality from cardiovascular disease and a 25% reduction in raised blood pressure under the Global Action Plan for the Prevention and Control of NCDs. Reducing salt intake is one of the 16 “best buys,” which are considered to be the most cost-effective and feasible for implementation in low-and lower middle-income countries, advocated by the WHO to tackle noncommunicable diseases (NCDs).
To bring about reduction in salt intake, we need to identify the sources of dietary sodium and estimate the sodium/salt intake and regularly monitor the same. Reducing salt intake is inevitable to bring about a reduction in morbidity and mortality related to excessive salt intake.
This paper presents a review of the methods of dietary sodium estimation under the following headings:
- Sources of dietary sodium
- Methods for estimation of dietary sodium intake
- Dietary estimation
- 24 h dietary recall
- Food frequency questionnaire (FFQ)
- Diet record
- Limitations of dietary sodium estimation methods.
- Biochemical estimation
- 24 h urine collection
- Overnight urine collection
- Spot urine collection
- Limitations of biochemical estimation.
- Important studies estimating dietary sodium intake
- INTERSALT (International Study of Salt and Blood Pressure).
- The INTERMAP (International Study of Macro-and Micro-Nutrients and Blood Pressure).
- Conversion of spot urine sodium into estimates of 24 h sodium excretion.
| Sources of dietary sodium|| |
Sodium is used in our diet for various reasons. Adding flavor is probably its most well-known function. It can also be used as a preservative to keep food safe, enhance a food's color or give it a firmer texture. For example, sodium in the form of baking soda (sodium bicarbonate) is used to help bread and other baked goods rise. Even though sodium plays a key role in many foods, more sodium in the form of salt is often added than is necessary.
The sources of dietary sodium can be found using 24-h dietary recall, FFQ, or diet record. Majority of the sodium in our diet comes from the salt that is added while preparing or processing the food, or at the table while consuming the food. Unprocessed foods such as fruits, vegetables, whole grains, nuts, meat, and dairy foods are low in sodium.
Sources of dietary sodium are known to vary between countries. In developed countries, the predominant source of sodium in diet is processed foods. In Mexico, Turkey, and Brazil, bread followed by processed food was found to be the main source of dietary sodium.,, In the Asian countries, the main source of dietary salt was the salt added while cooking, i.e., discretionary salt.,,,,, Identification of the major sources of sodium helps us in controlling the daily sodium intake.
Methods for estimation of dietary sodium intake
Dietary sodium intake can be estimated by either dietary estimation or biochemical estimation. In biochemical estimation method, sodium excretion of urine is used, as most of the consumed sodium gets excreted in the urine. Sodium excretion gives an estimation of salt intake.
24 h dietary recall
This method is designed to capture all food and drinks consumed in a period of 24 h. The distribution of single daily intake may show a strong variation. Interviewing in a subsample on a different day (ideally on a weekday and one weekend) to calculate the usual intake will give an estimation of sodium intake.
Food frequency questionnaire
The FFQ includes a limited list of foods and beverages and responses to indicate how often each item was consumed over a specified period of time. FFQ can capture typical intakes rather than a single day of intake. In general, FFQ does not include questions about salt added in cooking or at the table.
It is a detailed description of the types and amounts of foods, beverages, and supplements consumed over a specified time period. It is more reliable but requires a high level of knowledge and motivation. It may require training about accurate record intakes.
Limitations of dietary sodium estimation methods
Dietary estimation methods are considered to be more practical for conducting field surveys. However, there are certain limitations which include: Quantifying accurately the amount of sodium chloride added during cooking (including at restaurants) and at the table; variation in the proportion of salt added during cooking that is retained by the food (i.e., salt left behind on the plate); and variation in the sodium content of manufactured foods and in the sodium concentration of local water supplies.
Dietary assessment also allows the linking of sodium intake with dietary patterns or intake of other nutrients (such as potassium) associated with disease-related outcomes in order to inform public health interventions. Sodium intake is highly correlated with energy intake so that if the dietary assessment tool is significantly underestimating total food intake (and therefore total energy intake) then there will be a comparable underestimation of dietary sodium from food sources.
Dietary recall, weighed diet records, food diary, and FFQ are the various methods used for assessing nutrient intakes and are labor intensive for both participants and researchers. While the validity of dietary assessment tools is variable, they are essential for informing public health interventions for dietary sodium reduction, as they enable identification of sources of sodium intake. Identification of foods associated with high intake in different populations and cultural groups is essential to inform public health interventions based on reformulation of processed foods, and consumer education, and changing dietary practices.
24 h urine collection
Here, 24-h urine sodium is estimated. This method is often used to compare and validate other methods. Multiple nonconsecutive 24-h urine sodium is considered the gold standard method.
Overnight urine collection
Low-burden alternative to 24-h collection as fewer voidings are required, and the participant does not have to continue the collection during daily activities. However, it may be biased because of the marked diurnal variation in sodium excretion.
Spot urine collection
This method is a convenient and affordable alternative to 24-h urine collection. This can be used when a calibration study for use of spot urine has been done in the specific population of interest.
Limitations of biochemical estimation
Biochemical estimation, though considered a better and more objective method also, has its limitations. For example, factors that can affect sodium absorption, metabolism, and excretion, can alter the sodium intake estimation using urinary sodium excretion. In homeostasis, kidneys handle most of the sodium consumed in a day, and approximately 90%–95% of sodium is excreted in the urine within 24 h. To capture the marked diurnal variation in sodium, chloride, and water excretion, 24 h period is necessary. Electrolyte excretion in healthy individuals reaches a maximum at or before midday, and a minimum at night toward the end of sleep.
The 24-h urinary excretion method takes no account of electrolyte loss other than through the kidney and therefore will tend to underestimate true intake. Losses of sodium in the feces are small; losses through sweat are minimal in temperate climates but can be considerable in certain conditions.
Unlike most dietary methods, the 24-h urine collection is not prone to reporting biases. However, 24-h urine sodium estimation has its own share of disadvantages, such as:
- Due to high burden on the participant, rates of attrition may be high
- Estimates are dependent on sample collection volume
- There is no absolute check on completeness of sample collection (though the sodium/creatinine ratio and para-aminobenzoic acid marker have been used)
- The collection must be accurately timed to avoid over as well as undercollection and so that minor deviations from a 24-h collection period can be corrected.
Important studies estimating dietary sodium intake
Twenty-four hour urine collection has been used to assess population sodium intake in the landmark INTERSALT (International Study of Salt and Blood Pressure) study, which estimated dietary sodium intake. INTERSALT collected standardized data on 24-h urinary excretion of sodium among 10,079 men and women (aged 20–59 years) from 52 population sample clusters in 32 countries, this was by far the most extensive set of standardized data on 24-h urinary sodium excretion patterns around the world. Across the centers, median sodium levels ranged from 4.6 to 5.6 g/24 h and was significantly related to blood pressure in individuals. On multiple regression, a difference of 100 mmol/day in average population sodium intake corresponded to 2.2 mmHg lower systolic pressure.
The INTERMAP (International Study of Macro-and Micro-Nutrients and Blood Pressure) included measurements of dietary sodium intake and urinary sodium excretion from men and women, aged 40–59 years, from 17 population samples in four countries. Mean sodium excretion of the total 4680 participants was 4165 mg. The participants were divided into quartiles based on the excretion of sodium. With control for age, sex, and sample only, systolic blood pressure and diastolic blood pressure were consistently higher for those in the highest, compared with those in the lowest quartile of sodium excretion.
Conversion of spot urine sodium into estimates of 24 h sodium excretion
Spot urine sodium has been considered to be an affordable alternative to 24 h urine sodium. There have been few published formulae or equations to convert spot urinary sodium into estimates of 24 h excretion [Table 1]. Two have been derived in Japanese populations by Tanaka et al. and Kawasaki et al., One equation has been proposed by the Pan American Health Organisation (PAHO), the regional office of the WHO (the PAHO formula), and one equation derived from analysis of data from the INTERSALT study in North American and European populations., Toft equation was developed for the Danish population. The various variables used in these equations are age, weight, height, sex, spot urine sodium, spot urine potassium, and spot urine creatinine. The choice of formula depends on the population being studied. The sodium intake calculated using these equations only gives us the estimate of population-level sodium intake and not of the individual.
|Table 1: Equations used for the conversion of spot urine sodium to 24 h urine sodium|
Click here to view
The studies which compared the mean dietary salt intake based on spot urine sodium and 24 h urine sodium showed that the estimate of daily salt intake calculated with spot urine sodium is dependent on the equation used. Kawasaki equation was found to overestimate the daily intake, and the INTERSALT equation gave an estimate comparable with the 24 h urine sodium in some studies.,,,, More calibration or validation studies are required to find the appropriate equation for any particular region of the world.
| Conclusion|| |
Salt reduction at the population level is one important component in reducing cardiovascular diseases. Dietary sodium intake can be estimated by either dietary estimation or biochemical estimation. Estimates based on the food diary, weighed records, food-frequency questionnaire, or 24-h dietary recall tend to underestimate sodium intakes as compared with 24-h urine collections. Hence, 24-h urinary sodium excretion has become the preferred method of obtaining data on sodium intakes in population surveys. However, from a practical point of view, the spot urine or casual urine sample collection is more feasible for participants and is the preferred method for large population and surveys.
Salt reduction at population level has been identified as one of the top five priority interventions to prevent NCDs based on certain parameters such as health effects, cost-effectiveness, low implementation costs, and financial and political feasibility. In order to reduce the growing burden caused by the NCDs, the countries all over the world should take measures for reduction of salt consumption at the population level.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Patel S. Sodium balance-an integrated physiological model and novel approach. Saudi J Kidney Dis Transpl 2009;20:560-9.
] [Full text]
Dahl LK. Possible role of salt intake in the development of essential hypertension. 1960. Int J Epidemiol 2005;34:967-72.
Powles J, Fahimi S, Micha R, Khatibzadeh S, Shi P, Ezzati M, et al.
Global, regional and national sodium intakes in 1990 and 2010: A systematic analysis of 24 h urinary sodium excretion and dietary surveys worldwide. BMJ Open 2013;3:e003733.
Johnson C, Praveen D, Pope A, Raj TS, Pillai RN, Land MA, et al.
Mean population salt consumption in India: A systematic review. J Hypertens 2017;35:3-9.
Aburto NJ, Ziolkovska A, Hooper L, Elliott P, Cappuccio FP, Meerpohl JJ. Effect of lower sodium intake on health: systematic review and meta-analyses. BMJ 2013;346:f1326.
Malta D, Petersen KS, Johnson C, Trieu K, Rae S, Jefferson K, et al.
High sodium intake increases blood pressure and risk of kidney disease. From the science of salt: A regularly updated systematic review of salt and health outcomes (August 2016 to March 2017). J Clin Hypertens (Greenwich) 2018;20:1654-65.
Meneton P, Jeunemaitre X, de Wardener HE, MacGregor GA. Links between dietary salt intake, renal salt handling, blood pressure, and cardiovascular diseases. Physiol Rev 2005;85:679-715.
Antonios TF, MacGregor GA. Deleterious effects of salt intake other than effects on blood pressure. Clin Exp Pharmacol Physiol 1995;22:180-4.
Perin MS, Cornélio ME, Oliveira HC, São-João TM, Rhéaume C, Gallani MBJ. Dietary sources of salt intake in adults and older people: A population-based study in a Brazilian town. Public Health Nutr 2019;22:1388-97.
D'Elia L, Brajović M, Klisic A, Breda J, Jewell J, Cadjenović V, et al.
Sodium and potassium intake, knowledge attitudes and behaviour towards salt consumption Amongst adults in Podgorica, Montenegro. Nutrients 2019;11:E160.
Rodrigues SL, Souza PR Jr., Pimentel EB, Baldo MP, Malta DC, Mill JG, et al.
Relationship between salt consumption measured by 24-h urine collection and blood pressure in the adult population of Vitória (Brazil). Braz J Med Biol Res 2015;48:728-35.
Ribič CH, Zakotnik JM, Vertnik L, Vegnuti M, Cappuccio FP. Salt intake of the Slovene population assessed by 24 h urinary sodium excretion. Public Health Nutr 2010;13:1803-9.
World Health Organization. Draft Comprehensive Global Monitoring Framework and Targets for the Prevention and Control of Noncommunicable Diseases: Formal Meeting of Member States to Conclude the Work on the Comprehensive Global Monitoring Framework, Including Indicators, and a Set of Voluntary Global Targets for the Prevention and Control of Noncommunicable Diseases: Report by the Director-General. Available from: http://www.who.int/nmh/global_monitoring_framework/gmf1_large.jpg?ua=1
. [Last accessed on 2020 Apr 11].
World Health Organization. Tackling NCDs: 'Best Buys' and Other Recommended Interventions for the Prevention and Control of Noncommunicable Diseases. World Health Organization; 2017. Available from: https://apps.who.int/iris/handle/10665/259232
. [Last accessed on2020 Apr 11].
Colin-Ramirez E, Espinosa-Cuevas Á, Miranda-Alatriste PV, Tovar-Villegas VI, Arcand J, Correa-Rotter R. Food sources of sodium intake in an adult Mexican population: A sub-analysis of the SALMEX study. Nutrients 2017;9:E810.
Erdem Y, Akpolat T, Derici Ü, Şengül Ş, Ertürk Ş, Ulusoy Ş, et al.
Dietary sources of high sodium intake in Turkey: SALTURK II. Nutrients 2017;9:E933.
Asakura K, Uechi K, Masayasu S, Sasaki S. Sodium sources in the Japanese diet: Difference between generations and sexes. Public Health Nutr 2016;19:2011-23.
Zhao F, Zhang P, Zhang L, Niu W, Gao J, Lu L, et al.
Consumption and sources of dietary salt in family members in Beijing. Nutrients 2015;7:2719-30.
Xu J, Wang M, Chen Y, Zhen B, Li J, Luan W, et al.
Estimation of salt intake by 24-hour urinary sodium excretion: A cross-sectional study in Yantai, China. BMC Public Health 2014;14:136.
Lu Z, Zhang X, Li J, Zhang J, Zhao W, Ma J, et al.
Dietary sodium intakes and resources among residents in Shandong province. Zhonghua Yu Fang Yi Xue Za Zhi 2014;48:7-11.
Johnson C, Santos JA, Sparks E, Raj TS, Mohan S, Garg V, et al.
Sources of dietary salt in North and South India estimated from 24 hour dietary recall. Nutrients 2019;11:E318.
Ravi S, Bermudez OI, Harivanzan V, Kenneth Chui KH, Vasudevan P, Must A, et al.
Sodium intake, blood pressure, and dietary sources of sodium in an adult south Indian population. Ann Glob Health 2016;82:234-42.
Defagó MD, Perovic NR. Nutritional epidemiological tools for sodium intake. J Hypertens (Los Angel) 2015;4:208.
McLean RM. Measuring population sodium intake: A review of methods. Nutrients 2014;6:4651-62.
Brown IJ, Tzoulaki I, Candeias V, Elliott P. Salt intakes around the world: Implications for public health. Int J Epidemiol 2009;38:791-813.
World Health Organization/Pan American Health Organization. Regional Expert Group for Cardiovascular Disease Prevention Through Populationwide Dietary Salt Reduction. Protocol for Population Level Sodium Determination in 24Hour Urine Samples; 2010. Available from: http://new.paho.org/hq/dmdocuments/2010/pahosaltprotocol.pdf
. [Last accessed on 2020 Nov 11].
Kirkendall AM, Connor WE, Abboud F, Rastogi SP, Anderson TA, Fry M. The effect of dietary sodium chloride on blood pressure, body fluids, electrolytes, renal function, and serum lipids of normotensive man. J Lab Clin Med 1976;87:411-34.
Rose G, Stamler J. The INTERSALT study: Background, methods and main results. INTERSALT co-operative research group. J Hum Hypertens 1989;3:283-8.
Stamler J, Elliott P, Dennis B, Dyer AR, Kesteloot H, Liu K, et al.
INTERMAP: Background, aims, design, methods, and descriptive statistics (nondietary). J Hum Hypertens 2003;17:591-608.
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.
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.
Brown IJ, Dyer AR, Chan Q, Cogswell ME, Ueshima H, Stamler J, et al.
Estimating 24-hour urinary sodium excretion from casual urinary sodium concentrations in Western populations: The INTERSALT study. Am J Epidemiol 2013;177:1180-92.
Toft U, Cerqueira C, Andreasen AH, Thuesen BH, Laurberg P, Ovesen L, et al.
Estimating salt intake in a Caucasian population: Can spot urine substitute 24-hour urine samples? Eur J Prev Cardiol 2014;21:1300-7.
Santos JA, Rosewarne E, Hogendorf M, Trieu K, Pillay A, Ieremia M, et al.
Estimating mean population salt intake in Fiji and Samoa using spot urine samples. Nutr J 2019;18:55.
Meyer HE, Johansson L, Eggen AE, Johansen H, Holvik K. Sodium and potassium intake assessed by spot and 24-h urine in the population-based Tromsø study 2015-2016. Nutrients 2019;11:E1619.
Swanepoel B, Schutte AE, Cockeran M, Steyn K, Wentzel-Viljoen E. Monitoring the South African population's salt intake: Spot urine v. 24 h urine. Public Health Nutr 2018;21:480-8.
Zhou L, Tian Y, Fu JJ, Jiang YY, Bai YM, Zhang ZH, et al.
Validation of spot urine in predicting 24-h sodium excretion at the individual level. Am J Clin Nutr 2017;105:1291-6.
McLean R, Williams S, Mann J. Monitoring population sodium intake using spot urine samples: Validation in a New Zealand population. J Hum Hypertens 2014;28:657-62.
Bhargava M. Salt reduction strategy at population level. J Family Med Prim Care 2017;6:19-20.
] [Full text]
Beaglehole R, Bonita R, Horton R, Adams C, Alleyne G, Asaria P, et al.
Priority actions for the non-communicable disease crisis. Lancet 2011;377:1438-47.