ABSTRACT
Background
Intervention strategies to reduce sodium intake and increase potassium intake may decrease blood pressure; however, most are focused on reducing sodium in processed food globally.
Objectives
We attempt to fill important gaps in understanding the dynamics of these dietary determinants of hypertension in China.
Methods
We used data on 29,926 adults aged ≥20 y between 1991 and 2015 from an ongoing cohort, the China Health and Nutrition Survey. We collected detailed diet data with use of weighing methods with 3 consecutive 24-h recalls. With panel data random-effects models, we analyzed factors associated with sodium and potassium intakes and sodium to potassium (Na/K) ratios.
Results
Sodium intake decreased from 6.3 g/d in 1991 to 4.1 g/d in 2015, still twice the tolerable upper intake recommended by the WHO. Potassium intake was 1.7 g/d in 1991 and 1.5 g/d in 2015, below half that recommended by the WHO. The Na/K ratio decreased from 4.1 (ratios in g) in 1991 to 3.1 in 2015, 5 times the recommendation of the WHO. More than two-thirds (67%) of sodium intake was from salt added during food preparation, with 8.8% from processed foods in 2015, up from 5.0% in 1991. The most at-risk populations lived in China's central region and rural areas, were middle aged, had lower educations, or were farmers.
Conclusions
Sodium intake is very high across all regions in China. As part of sodium reduction efforts, China should target people living in the central region and adults aged above 60 whose sodium intakes are much higher. Strategies to decrease sodium intake and increase potassium intake should be different from those applied in the Western world where the major source is processed food. Reduced sodium higher potassium salts should become a major policy initiative in China.
Keywords: sodium, potassium, sodium to potassium ratio, sodium food sources, dietary trends, hypertension, China
Introduction
China is the epicenter of a major global increase in hypertension among low- and middle-income countries. Studies have shown that China's burden of mortality, morbidity, and disability from hypertension is the highest in absolute and relative terms globally (1–3). A recent study reported that the prevalence of hypertension was 44.7% among Chinese adults aged 35–75 y, accounting for 47.7% of the world's hypertensive population in this age group (4). Hypertension accounted for 28.0% of the total deaths and 15.0% of the total disability-adjusted life years in China (5).
Strong evidence has shown that high sodium intake increases hypertension and mortality from cardiovascular diseases (CVDs) (6–12). Sodium reduction decreases blood pressure in people either with or without hypertension and therefore decreases the combined CVD morbidity and mortality (13–17). A growing literature shows that increased potassium intake has the potential to reduce blood pressure, hypertension (18–22), and cardiovascular events (23–25). A reduced sodium to potassium (Na/K) ratio may provide weak but significant protection against hypertension (10, 26, 27). Nonetheless, the evidence is insufficient to estimate the relation between potassium or the Na/K ratio and hypertension and CVDs.
Evidence shows that sodium reduction strategies are low cost and effective, yet numerous initiatives to reduce sodium intake in the past 5 decades have had only minimal success in reducing sodium intake or hypertension (19, 27–33). In high-income countries, a very large proportion of sodium intake is from processed foods (34, 35). As a result, most strategies focus on reducing added sodium in packaged processed foods. In selected western European countries, the United States, and some other countries, major governmental initiatives have reduced sodium in processed foods (36–39).
To date, a few studies with a limited number of communities in China have reported that sodium intake was higher in the north than in the south (40, 41). No other longitudinal data are available, and few studies have explored sources and trends in sodium and potassium intakes among adults in China. To the best of our knowledge, China has not developed any sodium reduction strategies nationally. To develop approaches that can reach the most vulnerable individuals requires knowledge of current patterns and trends and the sources of the sodium consumed. This study examines a unique long-term cohort study of Chinese adults to achieve a better understanding of the current patterns, trends, food sources, and dynamics of sodium and potassium consumption in China as a basis for targeting prevention initiatives.
Methods
Study design and participants
The China Health and Nutrition Survey is an ongoing open cohort study initiated in 1989. We used a multistage, random cluster process to draw the sample surveyed in each of the following provinces from northeast to southwest: Heilongjiang, Liaoning, Jiangsu, Shandong, Henan, Hubei, Hunan, Guizhou, and Guangxi. We randomly selected 2 cities and 4 counties, stratified by income, in each province based on income amounts reported by the State Statistical Bureau in 1988. We added 3 megacities (Beijing, Chongqing, and Shanghai) in 2011 and 3 new provinces (Shaanxi, Yunnan, and Zhejiang) in 2015. We randomly selected 3 communities in each city or county and 20 households in each community and interviewed all household members. The design, sampling, and response rates are reported in-depth elsewhere (42, 43). Overall response rates, based on those who participated in previous surveys and remained in the current survey, were above 80% at the individual level and 90% at the household level.
We used data on 29,926 adults aged ≥20 y who provided 92,223 dietary records (or 3.1 records per person over time) from 1991 to 2015. The first China Health and Nutrition Survey data collected in 1989 that did not collect diet data on all adults are viewed more as a pretest and not used. The latest survey finished in 2019 is still being cleaned and organized. The institutional review committees of the University of North Carolina at Chapel Hill and the National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention, approved the survey protocols and instruments and the process for obtaining informed consent for this study. Participants provided their written, informed consent.
Diet measurement
We collected detailed diet data with use of weighing methods at the household level in combination with 3 consecutive 24-h recalls at the individual level. We carefully recorded and measured all food items and condiments in the home inventory with Chinese balance scales (graduation: 10 g) before 2004 and with digital diet and kitchen scales (graduation: 1 g) thereafter at the start of the first 24-h recall and at the end of the last 24-h recall in each survey. In addition, we disaggregated all mixed dishes by measuring all of the components of the recipe to allow accurate measurement at the household level. All interviewers participated in at least one 7-d training session and passed a comprehensive test before collecting any data.
We calculated sodium and potassium intakes based on the compositions in the Chinese Food Composition Table (FCT) (44) and have previously reported details (10). For food consumed away-from-home, we had no way to collect measurements of salt and other condiments added during cooking. To solve this problem, we conducted a study measuring and comparing sodium, potassium, and other compositions of identical dishes prepared at restaurants and stalls with the compositions of those prepared at home in urban and rural areas, and found that dishes prepared at restaurants contained at least 10% more sodium than the same dishes prepared at home (45). Therefore, we added 10% to the sodium in meals eaten away-from-home and conducted sensitivity analyses adding 5%, 10%, and 25% more sodium and not adding any sodium to meals eaten away-from-home. We used the mean of the 3 consecutive 24-h recalls in all analyses.
Previous validation studies have shown that our dietary data perform particularly well. In a validation of energy intake with doubly labeled water, our correlation was 0.56 for men and 0.60 for women, which is stronger than is shown in the literature (46). In another set of validation studies, we compared reported monosodium glutamate (MSG) intake with a urinary riboflavin marker, finding a correlation of 0.82 (P < 0.010) (47), and reported sodium and potassium intakes with urine sodium and potassium excretion via 24-h urine samples, finding a correlation of 0.58 and 0.59, respectively (P = 0.005) (10).
Statistical methods
We evaluated dietary behaviors and food consumption as potential predictors for sodium, potassium, and sodium to potassium ratio (Na/K ratio). For continuous variables, we applied general linear regression models and t tests to test differences among groups and trends. We tested categorical variables with chi-square tests. We separated residency into 3 regions based on geographic locations that are also linked with major dietary differences, north (Heilongjiang, Liaoning, Beijing, and Shaanxi), central (Shandong, Jiangsu, Henan, and Zhejiang), and south (Hubei, Hunan, Guangxi, Guizhou, Yunnan, and Shanghai). We grouped communities in large cities and county capital cities into urban areas and communities in highly rural suburban areas and rural villages into rural areas. We collected detailed income data from all sources, including demographic, economic, time-use, labor force participation, asset ownership, and expenditure data (48), inflated income to 2015 Chinese yuan value, and divided inflation-adjusted per capita household income into tertiles, low-, middle-, and high-income in all analyses. We collected detailed weeklong physical activity data including occupation activity, recreation and sports, transportation, and household chores on weekdays and weekends, converted all activities into metabolic equivalent tasks, and divided them into tertiles (49). We divided education into 2 categories, below high school and high school or higher. We defined smokers as those who ever smoked and alcohol drinkers as those who drank any alcoholic beverage at least once a month in the past year.
To examine the factors associated with dynamic changes in sodium and potassium intakes and Na/K ratio, we used time serial random-effects linear regression models to examine the demographic and economic factors associated with varying sodium, potassium, and Na/K ratio in the population. As the effects of time-invariant variables (e.g., gender) may be different over time, random-effects models are better approaches to estimate within-subject variance. We also used multinomial logit analyses, which generalize logistic regression by allowing more than 2 discrete outcomes, to examine the effects of these factors. Based on the WHO recommended reference intake (12, 27) and the newly released US DRIs (50), we defined 6 categories of sodium intake: <1.5 g/d, 1.5–1.9 g/d, 2.0–2.2 g/d, 2.3–4.1 g/d, 4.2–5.0 g/d, and >5.0 g/d; 4 categories of potassium intake: <1.6 g/d, 1.6–1.9 g/d, 2.0–3.5 g/d, and >3.5 g/d; and 5 Na/K ratios: <0.6 (ratios in g), 0.6–0.9, 1.0–1.9, 2.0–2.9, and ≥3.0. In multinomial logit analyses, we combined sodium intake <2.3 g/d into 1 group, potassium intake >2.0 g/d into 1 group, and an Na/K ratio <2.0 into 1 group because of the small sizes of these groups and used them as reference groups. We also conducted simulation analyses to examine the effects of regions on dietary sodium and potassium intakes and Na/K ratio. Based on the models we built with all sociodemographic factors, we predicted the mean intakes or proportion of intakes for each specific region by assigning a single value to the region variable and keeping all other variables unchanged. Comparing the predicted results with the unadjusted, real results from the survey data, we could understand the magnitude and direction of the effects of each region on sodium and potassium intakes and Na/K ratio. We cleaned, managed, and analyzed all the data with SAS software (version 9.4) and STATA (version 14).
Results
Sample characteristics
The sample changed in composition over time. In 1991, 84.2% of the participants did not have a high school education, but by 2015 that percentage decreased to 64.9%. The proportion rural remained approximately similar over time, while occupation and physical activity shifted dramatically away from labor-intensive activities, as the large declines in the metabolic equivalent tasks show. The gender composition remained constant, but the age distribution shifted toward a much older sample over time (Table 1).
TABLE 1.
Characteristics of Chinese adults aged ≥20 y, China Health and Nutrition Survey 1991–20151
| 1991 | 2000 | 2011 | 2015 | ||||
|---|---|---|---|---|---|---|---|
| 9 provinces | 9 provinces | 9 provinces | Megacities | 9 provinces | Megacities | New provinces | |
| Sample size, n | 8595 | 9937 | 9406 | 3239 | 9386 | 3091 | 2972 |
| Sample participated previously | 86.1 | 91.2 | 82.4 | 74.5 | |||
| Age, y | 42.2 ± 15.4 | 45.8 ± 15.2 | 52.0 ± 15.2 | 49.4 ± 14.4 | 53.3 ± 15.2 | 53.5 ± 14.6 | 47.0 ± 13.4 |
| 20–44 | 62.6 | 51.0 | 33.4 | 39.9 | 29.7 | 29.6 | 49.5 |
| 45–59 | 21.9 | 29.5 | 36.1 | 35.6 | 35.2 | 32.0 | 30.9 |
| ≥60 | 15.5 | 19.5 | 30.6 | 24.5 | 35.1 | 38.4 | 19.6 |
| Gender | |||||||
| Women | 52.0 | 51.6 | 53.0 | 53.3 | 53.0 | 53.4 | 53.2 |
| Men | 48.0 | 48.4 | 47.0 | 46.7 | 47.1 | 46.6 | 46.8 |
| Education | |||||||
| Below high school | 84.2 | 79.1 | 73.5 | 49.1 | 70.2 | 47.8 | 65.9 |
| High school and above | 15.8 | 20.9 | 26.5 | 50.9 | 29.8 | 52.2 | 34.1 |
| Adjusted per capita household income,2 1000 yuan | 3.3 ± 2.4 | 6.1 ± 6.3 | 15.6 ± 17.5 | 20.1 ± 17.6 | 21.7 ± 34.1 | 28.8 ± 41.6 | 19.5 ± 29.9 |
| Low tertile | 1.2 ± 0.5 | 1.6 ± 0.9 | 4.3 ± 4.6 | 4.1 ± 6.3 | 4.5 ± 4.6 | 4.7 ± 4.1 | 3.2 ± 7.3 |
| Middle tertile | 2.9 ± 0.5 | 4.7 ± 1.0 | 13.1 ± 2.8 | 13.7 ± 2.9 | 16.4 ± 3.9 | 17.1 ± 4.0 | 16.5 ± 4.0 |
| High tertile | 5.8 ± 2.5 | 11.8 ± 8.0 | 32.7 ± 23.3 | 32.8 ± 18.7 | 47.4 ± 51.7 | 47.9 ± 54.8 | 19.5 ± 45.8 |
| Region | |||||||
| North | 11.4 | 20.5 | 20.2 | 33.1 | 19.5 | 32.0 | 33.0 |
| Central | 37.8 | 33.9 | 34.1 | 33.1 | 32.5 | ||
| South | 50.8 | 45.6 | 45.6 | 66.9 | 47.4 | 68.0 | 34.5 |
| Urban/rural | |||||||
| Megacity | 60.5 | 59.3 | |||||
| Big city | 17.1 | 17.0 | 17.5 | 16.0 | 17.0 | ||
| Urban | 25.4 | 23.7 | 24.1 | 18.7 | 24.3 | 19.9 | 24.4 |
| Rural | 57.5 | 59.3 | 58.4 | 20.7 | 59.8 | 20.7 | 58.6 |
| Occupation | |||||||
| Farmer | 49.8 | 41.7 | 24.6 | 5.3 | 12.7 | 4.5 | 13.3 |
| Worker | 26.1 | 21.3 | 24.2 | 23.9 | 22.3 | 19.0 | 21.4 |
| Cleric | 5.1 | 5.4 | 4.7 | 10.8 | 4.7 | 10.2 | 10.0 |
| Manager | 11.1 | 6.4 | 5.2 | 13.5 | 5.6 | 12.0 | 7.6 |
| Not working | 7.9 | 25.3 | 41.4 | 46.5 | 54.8 | 54.2 | 47.6 |
| Physical activity, MET h/wk | 58.6 ± 37.6 | 37.5 ± 30.9 | 26.2 ± 27.3 | 17.9 ± 20.5 | 18.1 ± 21.2 | 12.4 ± 17.6 | 25.5 ± 29.7 |
| Low tertile | 18.8 ± 9.0 | 7.4 ± 5.6 | 3.4 ± 2.8 | 3.8 ± 2.8 | 1.9 ± 1.7 | 2.1 ± 1.7 | 2.0 ± 1.7 |
| Middle tertile | 54.2 ± 12.2 | 31.8 ± 8.4 | 16.2 ± 4.8 | 15.6 ± 4.5 | 11.1 ± 4.3 | 10.6 ± 4.2 | 11.9 ± 4.2 |
| High tertile | 102.8 ± 21.1 | 73.2 ± 23.2 | 53.1 ± 26.1 | 49.4 ± 27.7 | 40.6 ± 21.7 | 38.5 ± 25.7 | 47.8 ± 3 2.9 |
| Smoker (both women and men) | 32.6 | 28.8 | 30.6 | 30.7 | 27.1 | 24.6 | 28.4 |
| Women | 4.7 | 4.4 | 4.1 | 1.8 | 2.6 | 1.5 | 0.7 |
| Men | 62.8 | 54.9 | 60.5 | 63.6 | 54.6 | 50.9 | 60.0 |
| Drinker (both women and men) | 35.1 | 31.4 | 32.6 | 37.8 | 28.2 | 24.5 | 31.0 |
| Women | 12.6 | 9.2 | 9.5 | 17.2 | 5.5 | 5.2 | 9.2 |
| Men | 59.5 | 55.1 | 58.6 | 61.4 | 53.7 | 46.5 | 55.7 |
| Refrigerator ownership | 17.5 | 39.7 | 77.5 | 95.9 | 90.3 | 97.6 | 92.7 |
Values are given as means ± SDs, or %, unless otherwise indicated. MET, metabolic equivalent tasks.
Per capita household income adjusted by consumer price index to 2015 Chinese yuan value.
Sodium intake and sources over time
Overall sodium intake decreased but was still very high. On average, sodium intake among the 9 provinces in the original cohort was 6.3 g/d in 1991 and decreased to 4.1 g/d in 2015 (Table 2). Among the 3 megacities, it decreased from 4.1 g/d in 2011 to 3.9 g/d in 2015. The mean sodium intake among the 3 new provinces was 4.3 g/d in 2015. (Because the trends and magnitudes of intake did not change after we combined the 3 megacities, the 3 new provinces, and the 9 provinces in the original cohort, we do not present the results separately below. We still present them separately in the tables.) Only 15.4% of the participants consumed sodium ≤2.0 g/d in 2015, the tolerable upper intake recommended by the WHO (12), but that was an increase of 5.1% from 1991 (Figure 1). In 2015 sodium intake in the central region was significantly higher than that in the north region (P < 0.05) and that in the south region (P < 0.01). The mean sodium intake was higher in the 3 new provinces enrolled in 2015 (P = 0.001) but lower in the 3 megacities enrolled in 2011 (P < 0.001) (Table 2), compared to that in the original cohort.
TABLE 2.
Sodium and potassium intakes and Na/K ratio among Chinese adults aged ≥20 y, China Health and Nutrition Survey 1991–20151
| 1991 | 2000 | 2011 | 2015 | ||||
|---|---|---|---|---|---|---|---|
| 9 provinces | 9 provinces | 9 provinces | Megacities | 9 provinces | Megacities | New provinces | |
| Sample size, n | 8595 | 9937 | 9406 | 3239 | 9386 | 3091 | 2972 |
| Sodium intake, g/d | |||||||
| Mean | 6.3 ± 3.0 | 5.9 ± 2.9 | 4.5 ± 2.1 | 4.1 ± 2.2 | 4.1 ± 2.2 | 3.9 ± 2.2 | 4.3 ± 2.4 |
| North | 6.6 ± 3.2 | 5.3 ± 2.8 | 4.7 ± 2.3 | 4.5 ± 2.4 | 4.2 ± 2.2 | 4.3 ± 2.4 | 4.6 ± 2.6 |
| Central | 6.7 ± 3.1 | 6.5 ± 3.1 | 4.8 ± 2.3 | 4.4 ± 2.2 | 4.4 ± 2.2 | ||
| South | 6.0 ± 2.9 | 5.7 ± 2.7 | 4.2 ± 1.9 | 3.9 ± 2.1 | 3.9 ± 2.1 | 3.7 ± 2.0 | 3.8 ± 2.3 |
| Potassium intake, g/d | |||||||
| Mean | 1.7 ± 0.6 | 1.6 ± 0.7 | 1.6 ± 0.7 | 1.6 ± 0.7 | 1.5 ± 0.7 | 1.6 ± 0.7 | 1.5 ± 0.7 |
| North | 1.8 ± 0.7 | 1.6 ± 0.7 | 1.7 ± 0.7 | 1.7 ± 0.8 | 1.5 ± 0.6 | 1.7 ± 0.7 | 1.4 ± 0.6 |
| Central | 1.8 ± 0.6 | 1.7 ± 0.7 | 1.6 ± 0.6 | 1.6 ± 0.7 | 1.6 ± 0.6 | ||
| South | 1.7 ± 0.6 | 1.6 ± 0.7 | 1.6 ± 0.7 | 1.6 ± 0.7 | 1.5 ± 0.7 | 1.6 ± 0.7 | 1.6 ± 0.7 |
| Na/K ratio, g | |||||||
| Mean | 4.0 ± 2.3 | 4.0 ± 2.4 | 3.1 ± 1.9 | 3.0 ± 2.0 | 3.1 ± 2.4 | 2.8 ± 1.9 | 3.2 ± 2.4 |
| North | 4.3 ± 3.1 | 3.7 ± 2.3 | 3.2 ± 2.2 | 3.0 ± 1.9 | 3.2 ± 2.0 | 2.9 ± 1.9 | 3.8 ± 3.1 |
| Central | 4.0 ± 2.2 | 4.3 ± 2.5 | 3.4 ± 1.9 | 3.3 ± 3.1 | 3.1 ± 1.8 | ||
| South | 4.0 ± 2.2 | 4.0 ± 2.3 | 2.9 ± 1.7 | 2.9 ± 2.0 | 2.9 ± 2.0 | 2.7 ± 1.9 | 2.7 ± 2.0 |
Values are given as means ± SDs, unless otherwise indicated. Na/K ratio, sodium to potassium ratio.
FIGURE 1.
Distribution of sodium (A) and potassium (B) intake and Na/K ratio (C) among Chinese adults aged ≥20 y, China Health and Nutrition Survey 1991–2015 (n = 92,223).
We used sensitivity analysis to test if our assumption of adding 10% to the away-from-home measures of sodium affect our major results if we shifted that to lower levels of added sodium (adding only 5% more sodium) or higher levels (adding 15 and 25% more sodium). Adding 10% more sodium increased 6.5% and 10.4% of participants’ sodium intake in 1991 and 2015, respectively. The mean sodium intake increased by 0.011 g in 1991 and 0.014 g in 2015, respectively, compared to that without adding additional sodium. Panel data random-effects models showed that none of the regression coefficients changed more than 10% when adding 10% more sodium. Only 2 factors’ coefficients changed more than 10% when adding 25% more sodium (results not presented).
The sources of sodium intake did not significantly change over time. The major source was salt added during cooking, which accounted for 67% of the total sodium intake in 2015, down from 78.7% in 1991 among the original cohort. Processed foods other than condiments such as soy sauce and MSG were not an important source of sodium but nevertheless increased from 5% in 1991 to 8.8% in 2015 (Figure 2). Similarly, the sodium content of other natural foods (that is, nonprocessed food prepared at home and including food eaten away-from-home) increased from 7.5% in 1991 to 13.5% in 2015.
FIGURE 2.
Sources of dietary sodium intake among Chinese adults aged ≥20 y, China Health and Nutrition Survey 1991–2015 (n = 92,223).
Potassium intake and sources over time
Potassium intake was stable over time, 1.7 g/d in 1991 and 1.5 g/d in 2015. The differences among the 3 regions or among the original 9 provinces, the 3 megacities, and the 3 new provinces were not significant (Table 2). The major sources of potassium significantly changed over time. In 1991 the major sources were rice, grains, and leafy vegetables, while in 2015 the major sources were leafy vegetables, pork, and rice. The top 10 food sources contributed 69.5% of the total potassium intake in 2015, down from 86.4% in 1991 (Table 3) among the original cohort. Potassium from the top 10 food sources was similar in the 3 new provinces but lower in the 3 megacities.
TABLE 3.
Top 10 food sources of potassium intake among Chinese adults aged ≥20 y, China Health and Nutrition Survey 1991–2015
| 1991 | 2015 | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 9 provinces (n = 8595) | 9 provinces (n = 9386) | Megacities (n = 3091) | New provinces (n = 2972) | |||||||||
| Food name | Rank | Potassium, g/d | % of total potassium | Rank | Potassium, g/d | % of total potassium | Rank | Potassium, g/d | % of total potassium | Rank | Potassium, g/d | % of total potassium |
| Rice | 1 | 0.33 | 19.3 | 4 | 0.12 | 8.3 | 4 | 0.12 | 7.9 | 2 | 0.13 | 9.2 |
| Flour starch, rice/wheat | 2 | 0.27 | 16.0 | |||||||||
| Vegetables, leafy | 3 | 0.23 | 13.7 | 1 | 0.15 | 10.4 | 1 | 0.14 | 9.7 | 4 | 0.13 | 9.1 |
| Legumes and products | 4 | 0.16 | 9.2 | 6 | 0.11 | 7.5 | 6 | 0.07 | 5.1 | 6 | 0.10 | 7.2 |
| Vegetables, non-leafy | 5 | 0.14 | 8.1 | 5 | 0.12 | 8.2 | 3 | 0.12 | 8.1 | 5 | 0.12 | 8.4 |
| Starchy, roots | 6 | 0.11 | 6.6 | 3 | 0.12 | 8.4 | 5 | 0.10 | 6.7 | 3 | 0.13 | 9.2 |
| Pork | 7 | 0.10 | 5.9 | 2 | 0.12 | 8.5 | 2 | 0.13 | 8.6 | 1 | 0.13 | 9.3 |
| Flour starch, coarse grain | 8 | 0.05 | 3.1 | |||||||||
| Noodles, regular | 9 | 0.04 | 2.6 | 7 | 0.08 | 5.8 | 8 | 0.06 | 4.4 | 7 | 0.10 | 7.2 |
| Fish | 10 | 0.03 | 2.0 | 9 | 0.06 | 4.0 | 9 | 0.06 | 4.4 | 10 | 0.04 | 3.1 |
| Fruits | 10 | 0.05 | 3.4 | 10 | 0.06 | 4.1 | 9 | 0.05 | 3.4 | |||
| Dairy products | 7 | 0.07 | 4.8 | |||||||||
| Wheat buns, breads | 8 | 0.07 | 5.0 | 8 | 0.07 | 4.6 | ||||||
| Total | 1.48 | 86.4 | 1.02 | 69.5 | 0.93 | 63.9 | 1.02 | 70.6 | ||||
The Na/K ratio trends
Although the Na/K ratio decreased over time, it remained very high. On average, the Na/K ratio was 4.0 in 1991 and 3.1 among the original cohort, 3.2 in the 3 new provinces, and 2.8 in the 3 megacities in 2015 (Table 2). Only 1.8% of the participants (1.6% in the 3 megacities and 2.4% in the 3 new provinces) in 2015 had an Na/K ratio below 0.6, the ideal as recommended by the WHO (32). Patterns and trends in Na/K ratios were similar to those in sodium intake (Figure 1).
Factors associated with trends in sodium and potassium intakes and Na/K ratios
The major determinant of the distribution and overall sodium and potassium intakes was the region of residence (Table 4). Our results focused on factors associated with the distribution of sodium and potassium intakes and the Na/K ratio. People living in the central region had higher sodium intake and were more likely to have extremely high sodium intakes (>4.0 g/d), higher potassium intakes, and higher Na/K ratios than adults living in the south or in the north. Our simulation analysis showed that when compared to people in the central region, 10.6% fewer people in the north and 11.0% fewer people in the south would have sodium intakes >4.0 g/d in 2015, 8.4% fewer in the north and 6.5% fewer in the south would have Na/K ratios ≥3.0, while 3.7% more in the north and 6.6% more in the south would have potassium intakes <1.6 g/d in 2015 (Figure 3).
TABLE 4.
Factors associated with sodium intake, potassium intake, and Na/K ratio among Chinese adults aged ≥20 y, China Health and Nutrition Survey 1991–2015 (n = 92,223)1
| Sodium β (95% CI) | Potassium β (95% CI) | Na/K ratio β (95% CI) | |
|---|---|---|---|
| Region | |||
| North | −0.60 (−0.65, −0.55)2 | −0.04 (−0.06, −0.03)2 | −0.20 (−0.25, −0.15)2 |
| South | −0.72 (−0.76, −0.68)2 | −0.07 (−0.08, −0.06)2 | −0.27 (−0.31, −0.23)2 |
| Rural | 0.16 (0.12, 0.21)2 | −0.02 (−0.03, −0.00)3 | 0.20 (0.16, 0.24)2 |
| Women | −0.36 (−0.41, −0.32)2 | −0.17 (−0.18, −0.16)2 | 0.11 (0.07, 0.16)2 |
| Age group | |||
| Age 45–59 y | 0.18 (0.14, 0.22)2 | −0.02 (−0.03, −0.01)2 | 0.18 (0.15, 0.22)2 |
| Age ≥60 y | −0.11 (−0.16, −0.06)2 | −0.16 (−0.18, −0.15)2 | 0.40 (0.35, 0.45)2 |
| High school and above | −0.03 (−0.07, 0.02) | 0.06 (0.05, 0.07)2 | −0.13 (−0.17, −0.08)2 |
| Occupation | |||
| Farmer | 0.10 (0.03, 0.16)2 | 0.07 (0.05, 0.08)2 | −0.08 (−0.13, −0.02)2 |
| Worker | −0.10 (−0.15, −0.04)2 | 0.01 (−0.00, 0.03) | −0.08 (−0.13, −0.04)2 |
| Professional | −0.25 (−0.31, −0.18)2 | 0.01 (−0.01, 0.03) | −0.16 (−0.22, −0.10)2 |
| Income tertiles | |||
| Middle | 0.09 (0.05, 0.14)2 | 0.06 (0.05, 0.07)2 | −0.12 (−0.16, −0.08)2 |
| High | 0.07 (0.03, 0.12)2 | 0.12 (0.11, 0.13)2 | −0.28 (−0.32, −0.24)2 |
| Smoker | −0.05 (−0.10, −0.00)3 | −0.01 (−0.02, 0.00) | −0.00 (−0.05, 0.04) |
| Drinker | 0.11 (0.06, 0.15)2 | 0.06 (0.05, 0.07)2 | −0.08 (−0.12, −0.04)2 |
| PA METs tertile | |||
| Middle | 0.04 (−0.01, 0.08) | 0.03 (0.02, 0.04)2 | −0.04 (−0.08, 0.01) |
| High | 0.07 (0.01, 0.13)3 | 0.06 (0.05, 0.08)2 | −0.12 (−0.17, −0.07)2 |
| Survey year | |||
| 1993 | −0.18 (−0.25, −0.10)2 | −0.01 (−0.03, 0.01) | −0.03 (−0.10, 0.03) |
| 1997 | −0.43 (−0.50, −0.35)2 | −0.07 (−0.09, −0.05)2 | 0.01 (−0.05, 0.08) |
| 2000 | −0.45 (−0.53, −0.38)2 | −0.07 (−0.09, −0.06)2 | −0.04 (−0.11, 0.02) |
| 2004 | −1.39 (−1.47, −1.31)2 | −0.09 (−0.11, −0.07)2 | −0.67 (−0.74, −0.60)2 |
| 2006 | −1.59 (−1.67, −1.52)2 | −0.05 (−0.07, −0.03)2 | −0.91 (−0.97, −0.84)2 |
| 2009 | −1.87 (−1.94, −1.79)2 | −0.02 (−0.04, 0.00)2 | −1.14 (−1.21, −1.07)2 |
| 2011 | −1.81 (−1.89, −1.74)2 | −0.07 (−0.09, −0.05)2 | −0.96 (−1.03, −0.90)2 |
| 2015 | −2.12 (−2.19, −2.05)2 | −0.13 (−0.15, −0.11)2 | −1.03 (−1.09, −0.96)2 |
| _cons | 6.73 (6.64, 6.82)2 | 1.73 (1.71, 1.76)2 | 4.21 (4.13, 4.29)2 |
Multivariate regression coefficients (β) and 95% CI are derived from time-serial random-effects models.
P < 0.01.
P < 0.05.
FIGURE 3.
Simulated patterns of sodium (A) and potassium (B) intake and Na/K ratio (C) among Chinese adults aged ≥20 y by region, China Health and Nutrition Survey 1991–2015 (n = 92,223). We used multinomial logit analyses, which generalize logistic regression by allowing more than 2 discrete outcomes, to examine the effects of region. Based on the multinomial logit regression models, we predicted sodium and potassium intake and Na/K ratios for each region by controlling for age group, sex, education level, occupation type, income tertile, physical activity tertile, smoking status, drinking status, urban/rural residence, and survey years.
Aside from the large differences among the regions in sodium and potassium consumption patterns, the occupation of farmer and living in a rural area were the factors that impacted distribution of sodium and potassium consumption and the Na/K ratio among the regional subpopulations. Middle-aged adults were more likely to have higher sodium intakes and lower potassium intakes compared to younger or older age groups. Women were more likely to have lower sodium intakes and lower potassium intakes compared to men, but this is probably a reflection of lower energy intakes.
Discussion
Sodium intake has gradually decreased in China in the past 3 decades, but the intake is still twice the WHO recommendation of <2.0 g/d (12). In 2015, 81.7% of the Chinese population had sodium intakes higher than the DRI's Chronic Disease Risk Reduction intake (<2.3 g/d) (50), down from 93% in 1991. More than a quarter of people had a sodium intake >5.0 g/d. Sodium intake was lower in big cities and megacities, but it was still very high.
This research contrasts significantly with much smaller studies that have been heavily cited and used in the past. The International Study of Electrolyte Excretion and Blood Pressure and the International Population Study on Macronutrients and Blood Pressure, which were based on 2 communities/villages in the north and 1 in the south of China, reported in the late 1980s or 1990s that sodium intake was higher in the north than in the south (41). In contrast, our larger, more diverse sample showed that the highest sodium intake occurred in central China, most likely related to the 2 popular cuisines in this area, Huaiyang and Lu. Both cuisines use salt and large amounts of soy sauce during preparation. This region also has reported high incidence of stomach cancer related to high consumption of fermented products and salty preserved fish (51).
Added salt is still the most important source of sodium. More than 67% of total sodium consumption was from salt added during cooking in 2015. Among poor, low-educated, and rural residents, salt may be the only source of sodium. Sodium intake from processed foods and MSG, which is still low when compared to other sources of sodium intake, is increasing, particularly among higher-income, higher-educated, and urban residents.
Several factors may have contributed to the overall decrease in sodium intake in China. The first may be caused by improvement in food transportation and farming technology. In the past, fresh vegetables and meats were rarely available in the winter, particularly in the north. People consumed many salty and pickled foods for a great portion of the year. Marked advancements in food transportation and farming technology have significantly decreased pickled food consumption. This has been a national trend, as salted fish and other salted preserved foods are consumed much less than in the past. Moreover, refrigeration and greater purchases of packaged processed foods have contributed to a marked shift away from traditional preserved foods high in sodium (52). When we initiated this survey in 1989, salt was the major food preservative in China. Today over 90% of Chinese households own refrigerators and most of the population has access to modern retail outlets. Modernization and urbanization have reduced the need to use salt for food preservation. Although the Chinese government, under the leadership of the Chinese Nutrition Society and the National Institute for Nutrition and Health, has launched numerous campaigns and studies focused on salt reduction along with more localized actions in the past 15 y, no rigorous evaluation of these activities has been accomplished. In addition, the aging of the Chinese population is an important demographic factor that needs to be considered in average per capita statistics. As noted in our analysis, elderly people consume less food and therefore less sodium.
By contrast, potassium intake was very low and did not change over this same time. About 81% of the population had potassium intake <2.0 g/d, and only 1.7% reached the WHO recommendation of 3.5 g/d (27). Potassium intake was higher in the large cities except Chongqing, but the intake was not significantly different among the various regions. Potassium intake did not vary by geography, income, gender, or age group. In the Chinese diet the major sources of potassium are leafy vegetables, pork and pork products, and rice. This is in marked contrast to the potassium-rich foods bananas, sweet potatoes, and spinach (44).
The Na/K ratio was very high, 5 times higher than the WHO recommendation (12, 27), although it has decreased in the past 2 decades. More than 40% of the population had Na/K ratios >3.0 in 2015, while only 1.8% had ratios lower than 0.6, the WHO recommendation (12, 27).
Our results show that farmers and people living in rural areas are more likely to consume more sodium and have high Na/K ratios. Usually, these groups have heavier physical activities and consume more food than other subpopulations. Relatively, they are poorer and have less education, and they have fewer opportunities to learn about or participate in sodium reduction campaigns. Other research our group has conducted shows that diagnosis and treatment for hypertension is also lower among these subpopulations (53).
This is the only study to date that provides a longitudinal analysis of sociodemographic factors linked with differentials in sodium and potassium intakes. This study minimized many common reporting errors by weighing all foods and seasonings consumed over a 3-d period and disaggregating the exact ingredients each household used in all prepared dishes each day. No other study has had the size and heterogeneity to study these patterns and trends. Nonetheless, there are some limitations. Our survey does not cover the far western regions of China where the different dietary patterns might be linked with different sodium and potassium intakes. Although our results are consistent with those from China's cross-sectional, national representative surveys, we should be cautious to extrapolate our results to these regions. Second, we might have underestimated sodium intakes in recent survey years. Away-from-home eating including online-linked home delivery, snacking, and processed food consumption are increasing rapidly in China (52, 54), and the Chinese FCTs do not accurately capture the varying sodium content of these foods or dishes. This is a common problem globally, as FCTs are slow to reflect sodium changes in packaged processed foods. Evidence shows that sodium reductions in the United States, the United Kingdom, and other higher-income countries are not reflected in the same foods in low- and middle-income countries. Third, we used the mean of three 24-h recalls to represent sodium and potassium intakes, which may overestimate or underestimate the intakes and do not account for individual day-to-day variance. Another limitation is that we did not measure 24-h urinary sodium and potassium excretions, the preferred method of estimating total sodium and potassium intake data in a population survey.
In this study, we tried to adjust the underestimation resulting from away-from-home eating by adding 10% more sodium to dishes consumed away-from-home. This may not accurately estimate the amount of sodium added to dishes not prepared at home, because the 10% more sodium from 1 of our survey provinces may not apply for all other provinces. Some of the most commonly consumed dishes in 1 province may not be commonly consumed in other provinces. However, adding 10% more sodium to those dishes may compensate for the underestimation of sodium intake from dishes consumed away-from-home. We did several sensitivity analyses to test the differences in intake between adding various percentages of sodium (5%, 10%, 15%, and 25%) to dishes consumed away-from-home and without adding any sodium. The results showed that adding 10% more sodium to dishes consumed away-from-home does not change the trends and magnitudes of dietary sodium and potassium intakes and the association of related factors.
In conclusion, sodium intake in China has declined since 1991 but is still very high and varies by geography, with the highest intakes in the central region and among middle-aged populations, farmers, and people living in rural areas, which should be the targeted populations for sodium reduction programs. Potassium intake is very low and does not vary geographically or demographically. As a result, the Na/K ratios that may play an important role in developing hypertension and other CVDs are also very high. In addition, the salt options that replace sodium with potassium salts are more expensive, and careful evaluations of their organoleptic properties have not been undertaken. This is a major gap.
Unlike in the United States and other developed countries where 70.7% of sodium intake is from processed foods (55), in China the majority of the sodium consumed is from salt, MSG, and soy sauce added to dishes during food preparation. Therefore, Western world strategies to control sodium intake may be ineffective in China. While China has focused on reducing sodium intake, replacing sodium in salt with potassium to control and prevent hypertension should be considered.
The prevalence of hypertension is high among the Chinese population, and CVDs are a major burden on social, economic, and health resources, particularly in rural areas, where the burden is greatest. Reducing sodium intake is a public health priority and an opportunity for China to increase its population's health and quality of life. Public health approaches to reduce sodium intake may benefit from these data to tailor programs accordingly. Results from this study have helped spearhead a salt reduction campaign in Shandong, 1 of the central provinces, sponsored by the Chinese Center for Disease Control and Prevention and the US Centers for Disease Control and Prevention.
Acknowledgements
We thank Laura Cobb for her assistance. We thank Frances Dancy Burton, BS, for her helpful administrative assistance; Guifeng Jin, MS, and Karen R. Ritter, MS, for programming and technical support; and Emily Busey for graphic support. The authors’ responsibilities were as follows—BMP and SD: designed the research and wrote the manuscript; BZ and HW: conducted the research; SD: analyzed the data; BMP: had primary responsibility for the final content; and all authors: read and approved the final manuscript.
Notes
Supported by The Eunice Kennedy Shriver National Institute of Child Health and Human Development (R01 HD30880, P2C HD050924); the National Institute of Diabetes and Digestive and Kidney Diseases (R01 DK104371); the National Institutes of Health (NIH); the NIH Fogarty International Center (D43 TW009077); the National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention. This research used data from the CHNS. The analysis for this paper is funded by the Resolve to Save Lives program.
Author disclosures: The authors report no conflicts of interest.
Abbreviations used: CVD, cardiovascular disease; FCT, Food Composition Table; MSG, monosodium glutamate; Na/K ratio, sodium to potassium ratio.
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