TABLE 4.
Characteristics of the observational cohort and cross-sectional studies (2000–2014) examining the hypotensive effect of the sodium-to-potassium (Na:K) ratio1
| First author, year, country (ref) | Study design | Population | Sex: M/F | Age2 | Hypertension | Na/K assessment | Dietary intake measurement | Nutrient database | Exposure (Na:K ratio) | Outcomes | Adjustment factors |
| n | y | ||||||||||
| Du, 2014, China (37) | Ongoing open-cohort | China Health and Nutrition Survey (1991–2009) participants from all regions (north, south, central) | 8097/8772 | 20–60; mean: 37 at baseline | 10.4% at baseline | 24-h urine collection (used for validation purposes, authors report a lack of data for Na excretion) | Food and condiment weighing + 24-h dietary recall/3 consecutively in each survey | Chinese Food Composition Table3 | Dietary Na:K (mean in 1991–2009: 4.9–2.8) | Incident hypertension | Energy intake, age, sex, education, income, region, BMI, physical activity, smoking status, alcohol intake |
| Grubler, 2014, Austria (33) | Cross-sectional | Hypertensive patients derived from a tertiary care center (data from the Styrian Hypertension Study) | 102/109 | Mean: 60 | 100% | 24-h urine collection | Authors report use of urinary metrics rather than dietary metrics (“dietary salt intake reflected by 24-h urinary Na+/K+”) | NR | Urinary Na:K (mean: NR) | Nighttime SBP, nighttime DBP | SBP: sex, glycated hemoglobin, aldosterone:active renin ratio |
| DBP: age, sex, aldosterone:active renin ratio | |||||||||||
| Kim, 2014, Korea (34) | Cross-sectional | Korean adults who were recruited in the baseline surveys of the MRCohort | 2443/3840 | 40–89; mean: 62/60 (M/F) | 0 | FFQ used to estimate intakes | 106-item FFQ | Food Composition Table of Korea, 7th edition | Dietary Na:K (median in 1st–5th quintile: 0.8–1.94 in men; 0.69–1.91 in women) | SBP, DBP | Sex-stratified models: age, education, farmer status, physical activity, marital status, alcohol intake (men only), waist circumference (women only), fiber and calcium intakes |
| Mente, 2014, multiple (PURE study) (35) | Cross-sectional | Cross-sectional assessment of PURE study participants from 667 communities in 18 countries on 5 continents (42% from China) | 43,752/58,464 | 35–70; mean: 51 | Self-reported hypertension, 42%; not self-reported, 35% | Fasting morning urine collection and applying a formula-derived estimate of 24-h urinary excretion | Authors report use of urinary metrics rather than dietary metrics | NR | Urinary Na:K (mean: 2.33) | SBP, DBP | Age, sex, BMI, education, alcohol intake, geographic region |
| Millen, 2013, South Africa (15) | Cross-Sectional | Community sample of nuclear families with siblings aged >16 y | 137/194 | Mean: 40 | 26% | 24-h urine collection | Authors report use of urinary metrics rather than dietary metrics (“salt intake was indexed as urinary Na+/K+ in all analyses”) | 24-h urine excretion rates were calculated from the product of urine volume and urine electrolyte concentration | Urinary Na:K (mean: 4.18) | SBP, DBP | Age, sex, diabetes mellitus or glycosylated hemoglobin >6.5%, regular alcohol consumption, regular tobacco use |
| P values adjusted for nonindependence of family members | |||||||||||
| Zhang, 2013, U.S. (16) | Cross-sectional | NHANES, 2005–2010 | 5295/5268 | Mean: 41/50 (hypertensive/nonhypertensive) | 21% | Dietary recall used to estimate intakes (urine collections not available in NHANES 2005–2010 | 24-h dietary recall /supplements and antacids not included | USDA Survey Nutrient Database | Dietary Na, K, Na:K (mean: 1.41) | SBP, DBP, hypertension | Age, sex, race/ethnicity, BMI, education, use of table salt, smoking status, history of cardiovascular disease, self-reported chronic kidney disease, diabetes mellitus, alcohol use, physical activity; mutually adjusted for Na and K except in model for Na:K ratio |
| Hedayati, 2012, U.S. (17) | Cross-sectional | Probability sample of Dallas county residents | 1457/1846 | 30–65 (mean: 43) | 36% | First-void morning urine specimen | Authors report use of urinary metrics “rather than indirect measures such as dietary recall” | NR | Urinary Na:K (mean/median: 4.4/3.7 in AAs; 4.1/3.6 in non-AAs) | SBP, DBP, hypertension | Age, sex, race, diabetes mellitus, smoking, BMI, total cholesterol, estimated glomerular filtration rate, urine albumin:creatinine ratio |
| Michel, 2012, South Africa (18) | Cross-sectional | Community sample of nuclear families with siblings aged >16 y | 317/579 | Mean: 42/47 (Na:K ratio ≥median of 3.7 and <median of 3.7) | 46%/49% [Na:K ratio ≥3.7 (median) and <3.7] | 24-h urine collection | NR | 24-h urine excretion rates were calculated from the product of urine volume and urine electrolyte concentration | Urinary Na:K (median: 3.71) | SBP, DBP, PR, plasma angiotensin | Age, sex, BMI, regular tobacco use, regular alcohol use, diabetes mellitus/glycated hemoglobin >6.1%, antihypertension treatment |
| P values further adjusted for nonindependence of family members | |||||||||||
| Tzoulaki, 2012, multiple (INTERMAP) (36)4 | Cross-sectional | INTERMAP study: 17 population samples from Japan (4 samples), China (3 samples), United Kingdom (2 samples), United States (8 samples) | 2359/2321 | 40–59 (mean: 49) | 24% overall (Western/East Asian subjects: 27–32%/14–15% | 24-h urine collection | 24-h dietary recall (dietary supplements, foods, drinks recorded) | U.S. dietary data computerized using the Nutrition Data System, Nutrition Coordinating Center, University of Minnesota; in all other countries, dietary data entered onto standard forms, coded, and computerized | Urinary Na:K (mean Japan: 6.31; mean China: 4.23; mean U.K.: 2.23; mean U.S.: 3.04) | SBP, DBP | Age, sex, reported special diet, use of dietary supplements, moderate or heavy physical activity, doctor-diagnosed cardiovascular disease and diabetes mellitus, family history of hypertension, height, weight, and total energy intake |
| Huggins, 2011, Australia (19) | Cross-sectional | Subgroup of cohort study participants recruited opportunistically, with oversampling of southern European immigrants | 376/407 | Mean: 64 | 43% | 24-h urine collection | Discretionary salt use determined by a 2-question survey | NR | Urinary Na, K, Na:K (mean: 1.99) | SBP, DBP, hypertension | Continuous models adjusted for age, sex, BMI, country of birth, antihypertension medication use |
| Quintile models adjusted for age, sex, BMI, country of birth | |||||||||||
| Yang, 2011, U.S. (20) | Cross-sectional | Participants in the third NHANES | 5899/6368 | ≥20 | 21%/19% (M/F) | Dietary recall used to estimate intakes (urine collections not available in NHANES III) | 24-h dietary recall | USDA Survey Nutrient Database | Dietary Na, K, Na:K (mean M: 1.31; F: 1.23) | SBP, DBP, hypertension | None |
| Redelinghuys, 2010, South Africa (21) | Cross-sectional | Community sample of nuclear families with siblings aged >16 y | 221/414 | Mean: 45 | 43.6% | 24-h urine collection | NR | 24-h urine excretion rates were calculated from the product of urine volume and urine electrolyte concentration | Urinary Na:K (mean: 4.27) | PP, SBP, DBP, central hemodynamics | Age, BMI, sex, diabetes mellitus or glycosylated hemoglobin >6.1%, regular tobacco intake, regular alcohol intake, treatment for hypertension; mean arterial pressure adjusted for only in analyses of PP and central hemodynamics |
| P values further adjusted for nonindependence of family members | |||||||||||
| Ruixing, 2008, China (22) | Cross-sectional | Stratified randomized cluster sample of residents of 7 villages in Napo County, Guangxi | 834/835 | 15–84 (mean: 46) | 34%/19% (M/F) | Dietary recall analyzed to determine each subject’s dietary sodium and potassium intake (g/d) | 24-h dietary recall | 2002 Chinese Food Composition Table | Dietary Na, K, Na:K (mean: 1.1 in nonhypertensive M; 1.5 in hypertensive M; 1.4 in nonhypertensive F; 1.8 in hypertensive F) | Hypertension | NR |
| Polónia, 2006, Portugal (23) | Cross-sectional | Sample of 4 different adult populations living in northern Portugal | 187/239 | 20–71 (mean: 50) | NR | Average of 2 24-h urine collections for 162 participants/single 24-h urine collection for 264 participants | Daily salt intake based on calculation of 24-h urinary Na and assuming that all Na ingested was as NaCl | NR | Urinary Na, Na:K (mean: 1.9 in hypertensives; mean: ≤1.5 in nonhypertensives) | SBP, DBP, pulse wave velocity | None for SBP and DBP; age and SBP adjusted for in analysis of pulse wave velocity |
| Kwok, 2003, China (24) | Cross-sectional | Long-term (≥10 y) vegetarians recruited from religious organizations or old-age hostels | 0/111 | Mean: 78 | 64% | Fasting 20-mL urine specimen | 24-h dietary recall | Region-specific (Hong Kong) food composition tables | Urinary Na:K, dietary K (mean: 4.7 in hypertensives; mean, 3.4 in nonhypertensives) | SBP, DBP, hypertension | None in dietary K-hypertension analysis |
| Adjusted for urinary Na:creatinine ratio in urinary Na/K and SBP, DBP analyses | |||||||||||
| Age-adjusted in urinary Na/K and SBP, DBP, and hypertension analyses | |||||||||||
| Schröder, 2002, Spain (25) | Cross-sectional | Stratified randomized sample of general population of Gerona according to 1991 census | 758/809 | 45/59/62 (normotensives, untreated hypertensives, treated hypertensives) | 37% | Dietary recall analyzed to determine each subject’s dietary sodium and potassium intake (mg/d) | 72-h dietary recall | Diet Analysis Nutritionist IV; the database of this software was supplemented with 130 food items from Spanish food composition tables | Dietary Na, K, Na:K (mean: 0.60 in nonhypertensives; 0.62 in untreated hypertensives; 0.59 in treated hypertensives) | SBP, DBP, hypertension | Dietary Na/K and SBP, DBP analyses: age, sex, BMI, smoking and drinking status |
| Dietary Na analyses and SBP, DBP: age, sex, BMI, smoking and drinking status, calcium, K, magnesium | |||||||||||
| Dietary K analyses and SBP, DBP: age, sex, BMI, smoking and drinking status, calcium, Na, magnesium | |||||||||||
| Hypertension analyses: age, sex, BMI, alcohol and smoking status | |||||||||||
| Yamori, 2002, China (26) | Cross-sectional | Randomized cluster sample of male residents in Daping District of Chongqing, China | 177/0 | 43–55 (mean: 51) | 20% | 24-h urine collection | Questionnaire (NR; data to be presented in subsequent reports by the authors) | NR | Urinary Na, K, Na:K (mean: 4.55) | SBP, DBP, hypertension | Urinary Na and K analyses: none |
| Urinary Na/K: age, occupation, smoking, alcohol consumption, education, BMI, magnesium, total:HDL-cholesterol ratio, total protein, TGs | |||||||||||
| Hajjar, 2001, U.S. (27) | Cross-sectional | Participants in third NHANES | 8004/9026 | ≥20 (mean: 49) | NR | Dietary recall used to estimate intakes (urine collections not available in NHANES III) | 24-h dietary recall | USDA Survey Nutrient Database | Dietary Na, K, Na:K (mean: 1.22) | PP, SBP, DBP | Adjusted: age, sex, ethnicity, BMI |
| Multivariate: stepwise selection of demographic variables, BMI, dietary factors, and dietary factor interactions; model based on a random subsample of 8529 participants, then tested on remaining participants | |||||||||||
| Hu, 2001, China (28) | Cross-sectional | Two random stratified cluster samples, 3 y apart, in 6 districts in Tianjin | 990/1078 | 35–64 (mean: 47/54) (normotensive/hypertensive) | 37% | Food records or recall analyzed to determine each child‘s dietary sodium and potassium intake (mg/d) | Food weighing + 3-d food records or 24-h recall | Chinese Food Composition Tables | Dietary Na, K, Na:K (mean: 2.99 in nonhypertensive M; 3.13 in hypertensive M; 3.08 in nonhypertensive F; 3.34 in hypertensive F) | Hypertension | Age, energy, BMI, time of survey |
| Xie, 2001, China (29) | Cross-sectional | Stratified random sample of residents of an isolated farming village in Hubai Province | 191/162 | 14–75 (mean: 40/37) (M/F) | NR | 24-h urine collection | 24-h recall | 1991 Chinese Food Composition Table | Urinary Na, K, Na:K (mean: 6.1) | PP, SBP, DBP | Age, sex, height, weight, heart rate, serum total cholesterol |
| Caputo, 2000, U.S. (30) | Cross-sectional | Urban public 6th-grade students | 30/39 | 11–13 (mean: 12) | 0% | FFQs analyzed to determine each child‘s dietary sodium and potassium intake (mg/d) | FFQ jointly completed by parents and children | Nutritionist IV: Diet Analysis and Nutritional Evaluation | Dietary Na:K (mean: 0.96) | SBP, DBP | BMI, % body fat, family history of hypertension, physical activity, waist-to-hip ratio |
| Mosley, 2000, Egypt (31) | Cross-sectional | Household clusters in 6 governorates | 370/465 | Mean: 51/47 (M/F) | NR | 12-h urine collection | NR | NR | Urinary Na:K (median: 2.9 in M; median: 2.5 in F) | SBP | Male-only analysis: age, melanin index, and BMI |
| Female-only analysis: age | |||||||||||
| Mufunda, 2000, Zimbabwe (32) | Cross-sectional | Household clusters in Dombotombo township; restricted to residents in area for ≥3 y | 384/391 | ≥25 | 28%/41% (M/F) | Spot urine collection | NR | NR | Urinary Na:K (mean: 3.3 in M; mean: 3.4 in F) | SBP, hypertension | Hypertension analysis: age |
| SBP analysis: age, BMI, Shona ethnicity, tobacco use, alcohol use, months in rural area per year |
1
AA, African American; DBP, diastolic blood pressure; INTERMAP, International Study of Macro/Micronutrients and Blood Pressure; MRCohort, Multi-Rural Communities cohort; NR, not reported; PP, pulse pressure; PR, plasma renin; PURE, Prospective Urban Rural Epidemiology; SBP, systolic blood pressure; ref, reference.
2
The mean only is shown when the range is not provided.
3
The sodium and potassium compositions of a few foods imported or unavailable in Chinese markets were adopted from the food composition tables of Hong Kong, Taiwan, Japan, or the USDA.
4
NHANES data (4 cross-sectional cohorts: 1999–2000, 2001–2002, 2003–2004, 2005–2006) were used for external validation of the INTERMAP data.