Introduction
Water is a nutrient, which is essential for the survival and development of human’s life [
1]. Water modulates normal osmotic pressure, maintains electrolyte balance and regulates body temperature. The balance between water output and water input defines hydration. Both excessive and insufficient fluid intakes have negative impacts on health. If fluid intakes exceed the capacity of renal excretion (700–1000 mL/h), it results in acute water intoxication, and probably hyponatremia. However, this is very rare and only occurs in people with psychological problems, renal disease, liver disease or congestive heart failure. Inexperienced athletes, who rapidly rehydrated after a sport event and people who drink a large amount of water to avoid heatstroke in high temperature weather are also at risk of overhydrating. By contrast, dehydration occurs when the fluid intake is insufficient to replace the free water output is more common. Even mild dehydration or a low fluid intake may impair cognitive performance [
2‐
4], reduce the ability to perform physical activities [
5,
6] and increase the incidence and prevalence of kidney and urinary system diseases [
7‐
9]. Therefore, it is necessary to develop recommendations and guidelines for adequate intake (AI) of water and raise public recognition of the importance of maintaining an adequate water intake. The Chinese Nutrition Society has set age- and gender-specific AI for both total water intake (water from food moisture and fluids) and total fluid intake (TFI) (Table
1).
Table 1
Adequate total fluid intake in China (L/day) for individuals living in moderate climatic conditions with light physical activity [
21]
4–6 | 0.8 |
7–10 | 1.0 |
| Males | Females |
11–13 | 1.3 | 1.1 |
14–17 | 1.4 | 1.2 |
≥ 18 | 1.7 | 1.5 |
Pregnant women | – | 1.7 |
Lactating women | – | 2.1 |
Recommendations for adequate intake of water are usually developed based, at least partly, on observed survey data. However, the importance of water is often overlooked and there are not enough studies relating to fluid intake. In China, only two surveys have been conducted that focused on TFI (the sum of drinking water and all other beverages). The first was performed among 1483 adults aged 18–60 years [
10] and the second one among 5868 primary and middle school students aged 7–17 years from four cities in China [
11]; the surveys were conducted in the summer of 2010. The average daily water intake of male adults (1679 mL) was higher than that of females (1370 mL). Similarly, the average daily drinking water was significantly higher in boys (1157 mL) than in girls (1026 mL). The two surveys provided vital reference data for setting the AIs. However, more fluid surveys to provide data for future revisions of the AIs in China. In both the earlier surveys, there was a significant difference in median daily TFI for adults, primary and middle school students between the cities, namely, Beijing, Shanghai, Chengdu and Guangzhou city. These findings suggest that the fluid intake of residents in different regions in China might differ. In addition, potential disparities in China by SES (socioeconomic status) need to be explored.
In addition to the amount of TFI, the type of fluid consumed by individuals is also important and needs further investigation. The sources of daily TFI usually includes tap and bottled water, milk, tea, fruit juice, sugar sweetened beverages (SSB), coffee, soft drinks and other beverages. Substantial evidence has demonstrated that different fluid types have different effects on health. Excessive SSB consumption increases risk of dental caries [
12], weight gain [
13], obesity [
14], risk of developing the metabolic syndrome [
15], type 2 diabetes [
16], and dyslipidaemia [
17]. Data analysis of NHANES showed that the risk of chronic kidney diseases (CKD) varied among individuals with different type of beverages consumption with lower plain water being associated with an increased risk of CKD [
18,
19]. Thus, it is important to develop healthy drinking patterns based on adequate fluid intake. In China, the daily consumption of plain water, tea and other beverages has been shown to differ in adults and in children among four cities [
20]. To develop further recommendations and policies on types of fluid intake to promote health drinking habits, more surveys are needed to study drinking behaviors and choices in the Chinese population.
The present study assessed the total fluid intake and type of fluids among populations of different age group in a nation-wide, urban-based sample in urban China. The primary aim of this study was to report usual daily TFI amongst the population in urban China according to age group, gender, regions and city socioeconomic status. The secondary aim was to compare TFI with adequate intakes set by the Chinese Nutrition Society [
21]. And the final aim was to evaluate the contributions of different fluid types to TFI.
Discussion
The main objectives of the present study were to estimate the 7-day mean TFI and the different fluid types among a relatively large sample across seven regions based on geographical location in urban China according to age group, gender, regions and cities with different socioeconomic status, to assess the percentage of participants who comply with the adequate intake of water from fluids set by Chinese Nutrition Society, and to evaluate the contributions of fluid types to TFI.
Less than a half of children, approximately a third of adolescents and merely about a quarter of adult participants in this study reached the amount of AI, which means that a considerable portion of participants might be at the risk of being under-hydrated. In the previous fluid intake survey with the
Liq.In
7
record of children and adolescent in four Chinese cities conducted in China, the TFI of children and adolescents aged 7–17 years was 1086 mL/day which is higher than the TFI of children (966 mL/day) [
36] and lower than TFI of adolescents (1177 mL/day) in the current study [
10]. For adults, the TFI in current survey differed by only approximately 100 mL/day compared with the fluid intake survey of adults in four Chinese cities (1584 vs 1488, mL/day) in 2010 [
20]. In a survey with the
Liq.In
7
record specifically conducted in young adults (aged 18–25 years) in China in 2015, TFI was 1342 mL/day and less than the adults in this survey [
37]. In a systematic review including 273 studies in different countries (only one Asia survey in China was included; the majority being USA and European surveys), it was concluded that TFI varied between 0.6 and 3.5 mL/day in the general population and 0.6–1.8 mL/day amongst children, 0.8–2.0 mL/day amongst adolescents, and 0.8–3.4 mL/day amongst adults [
38]. Another survey using the
Liq.In
7
record in 2015 also indicated that only approximately a quarter of the Chinese young adults met the recommendation [
37]. Harmonized cross-sectional fluid specific surveys performed in 15 countries showed that a relatively high proportion of subjects (38%) failed to meet the recommendation on fluid intake and this proportion significantly varied among countries [
39]. However, the recommendation used in harmonized surveys was the EFSA AIs, not Chinese AI as used in the recent study; this may partly explain the different adherence levels were. The present survey suggests that some people in China are not meeting the AI although the exact prevalence requires further study.
In the present study, water was the fluid type consumed in the highest volume, followed by SSB and milk and its derivatives. In the fluid intake survey with the
Liq.In
7
record of children and adolescent in four Chinese cities in 2010, the contribution of water to TFI was also the highest in primary and middle school students and adults [
36] (68.3 and 60.3%). It is important to note that 27, 48 and 47% of children, adolescents and adults consumed more than one serving SSB per day, respectively, an intake, suggested by some studies that may result in harmful effects on health such as weight gain and dental caries [
40,
41]. Unsweetened tea is a suitable alternative to water and favored by residents in China; tea contributed nearly ten percent of TFI in this survey. In a systematic review including 273 studies, water contributed up to 58, 75 and 80% of TFI among children, adolescents and adults [
38]. In a fluid specific survey with the
Liq.In
7
record including 16,276 adults across 13 countries from three continents, the fluid with the highest intake was also water (except in Argentina, UK, Poland and Japan) and water intake ranged from 270 mL/day in Japan to 1780 mL/day in Indonesia; the second and third mostly consumed fluid was hot beverages and regular sweetened beverages in most countries [
19]. In the fluid intake survey of children and adolescent in four Chinese cities in 2010, the consumption of water in high school students was the highest (829 mL/day) and that in primary students was the lowest (672 mL/day) [
36]. In the aforementioned systematic review, TFI increased gradually among children, adolescents and adults with age; the consumption of fluid types varied according to age, whilst children consumed more milk, adolescents consumed more soft drinks, and adults drank more tea, coffee and alcoholic beverages [
38]. In the harmonized cross-sectional surveys of fluid intake using the
Liq.In
7
record, it was shown that children and adolescents were less likely to meet the recommendation of fluid intake than adults and the contribution of juices and sweet beverages was as high as the contribution of water to TFI [
39].
In this survey, it was shown that children and male adolescents chose healthier fluid types (more water and less SSB) than adolescent girls, while amongst adults women preferred better fluid types than men. Gender differences in TFI have previously been shown in primary and middle school students and adults in previous two surveys in China [
36] with adult men drinking more tea than women.
Comparisons between regions showed that there were significant differences on TFI, and TFI was highest in the south region of China. In terms of city different socioeconomic status, differences in TFI were also found among cities with different socioeconomic status with TFI being the highest in Tier 1 cities. The data might also suggest that lower SES groups (Tier 2 cities and Tier 3 cities) are disproportionately less likely to meet the AI. This is an important and novel finding as previous studies have not compared the even regions nor cities with different socioeconomic status in China. The landscapes and geographical location vary significantly across the vast width of China, which may result in the differences in TFI due to the different altitudes and environmental conditions. Analyzing the data from different regions may provide useful detailed data for future revisions of the water AI in China according to the geographical location. In the fluid intake survey with the
Liq.In
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record of adults in four Chinese cities in 2010, TFI was highest in Shanghai (east, 1793 mL/day), while least in Chengdu (west, 1150 mL/day); water intake was highest in Guangzhou (south, 917 mL/day); tea intake was highest in Shanghai; beverage consumption (including all types of beverages except water and tea) was higher in Shanghai and Beijing (north) (323 and 264, mL/day) [
42]. In the survey across 13 countries, there were considerable differences in the consumption of the different fluid types among countries; however, relatively similar fluid intake patterns were observed among countries located in the neighboring geographical area. It is important to recognize there may be discrepancies of educational level and socioeconomic status among cities with different socioeconomic status defined by the Chinese government based on the combination of GDP, administrative authorities and other economic criteria such as population size. In the previous fluid intake survey using the
Liq.In
7
record of adults in four Chinese cities in 2010, water intake in urban areas was less than rural ones, which was opposite for tea and beverages. In addition, educational level had an effect on the volume of beverages consumed [
42]. Some surveys have analyzed the effect of educational level and socio-economics status on TFI, and found that socioeconomic status was associated with TFI. In a study among US adults, it was observed that lower income adults had a higher risk of inadequate hydration than higher income adults [
43].
There were some strengths and limitations in the present study. In terms of strengths, this analysis was unique as it collected data on TFI of a relatively large sample with an equal gender distribution covering a relatively large part of China. This provides more representative data for developing recommendations and guidelines of adequate water intake. In addition, the study explores potential disparities among various populations. The use of a photographic booklet of standard fluid containers limited the self-reporting bias. The
Liq.In
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used in this survey has been validated for accuracy and reliability; however, this validation was performed in an American, adult population [
31]. Several limitations of the survey or the analysis need to be acknowledged. There is the potential for sampling design limitations, such as bias that may result if individuals who are not at home share characteristics that differ from those who are at home. The disadvantage of using a harmonized protocol is that some methods were used to enable inter-country comparisons that might not have been optimally sensitive for use in China; for example, the analysis protocol group beverages using the same categories as used in other countries, not China-specific categories. The prevalence of overweight and obese in the children sample was higher than that observed in the Chinese National Survey on Students Constitution and Health in 2014 [
44], and the proportion of participants living in urban areas was higher in this survey. Rural population was not included in this survey. Thus, the results may not be generalizable to whole population on a nationwide scale. Fluid intake from foods and food data were not assessed in the study, which prevents the estimation of total water intake. However, it might have increased the quality of the fluid data reported, as participants were focused on reporting all drinking acts. If participants had to report all food and fluids intake, drinking acts outside the regular meals may have been missed [
45]. Physical activities of subjects have not been investigated. Weighted analysis has not used in this study.
In conclusion, the current survey showed that TFI varies by gender, region and city socioeconomic status in urban China. A relatively large proportion of participants in the survey drank less than the AI of water from fluids, and are, therefore, potentially at risk of under-hydration. About half of the adolescents and adults consumed ≥ 1 serving SSB/day, an intake that may be associated with adverse effects on health. The results have potential implications for health disparities and emphasize the need for interventions that target particular groups, such as lower SES groups or particular regions. Effective interventions should be developed and implemented to increase fluid intake and improve beverage choice, while analyzing their efficacy. Health promotion policies and campaigns should encourage the creation of an environment favoring water consumption.