Association between parent-reported salt-related behaviors and estimated urinary salt excretion: a cross-sectional study of health checkups in 4-year-old children

TL;DR

This study found that how often parents report feeding high-salt foods to 4-year-olds is linked to the children's urinary salt levels and sodium-potassium ratios.

Contribution

The study provides new evidence linking parent-reported salt-related behaviors to objective urinary salt excretion in preschool children.

Findings

Low consumption of high-salt foods like pickles and noodles was associated with lower salt excretion and Na/K ratio.

Consuming half a bowl of udon or ramen was linked to higher Na/K ratios compared to eating an entire bowl.

Children who rarely ate out or had convenience-store bento had higher Na/K ratios than those who did so frequently.

Abstract

Although salt-related behaviors may influence urinary salt excretion in early childhood, this relationship remains unclear. This study aimed to examine salt-related behaviors using data from a salt check sheet and urinary salt excretion parameters using spot urine samples from 4-year-old children. This cross-sectional study included all 4-year-old children who underwent health checkups in Ohnan Town, Shimane Prefecture. The study sample consisted of 109 children (49 boys). Measures from spot urine samples included estimated salt excretion (g/day) and the sodium-potassium (Na/K) ratio. Salt-related behaviors were assessed using a salt check sheet that was completed by the parents or guardians. The associations between salt-related behaviors and urinary salt excretion parameters were analyzed using a generalized linear model. The median (M) and interquartile range (IQR) for urinary measures in 4-year-old children were as follows: estimated salt excretion (M = 4.4, IQR: 3.3–6.2) and Na/K ratio (M = 2.3, IQR: 1.4–3.3). The low frequency of consumption of high-salt foods (“such as pickles, pickled plums, etc.” and “noodles such as udon and ramen”) was associated with low salt excretion and low Na/K ratio. However, in the case of “consumption of udon, ramen, or other soups”, the Na/K ratio was higher for “About half a bowl” and “Some” than for “An entire bowl.” Additionally, for “eating out or having convenience-store-bought bento (lunch plate) for lunch”, the Na/K ratio was higher for “No” than for “Almost every day.” In conclusion, the frequency of high-sodium food intake was associated with both urinary sodium excretion and the Na/K ratio in 4-year-old children. Longitudinal investigations using the 24-hour urine collection method are needed to confirm these salt-related behaviors.

The online version contains supplementary material available at https://doi.org/10.1265/ehpm.25-00076.

Full text

Dear Editor:

The World Health Organization states that the recommended maximum sodium intake of 2 g per day for adults should be adjusted for children, considering the energy requirements of children compared to adults [1]. The Japanese Ministry of Health, Labour and Welfare recommends that the daily salt intake for children aged 3–5 years be <3 g [2]. The Japanese Society of Hypertension recently released a consensus statement regarding the practical application and target values of the urine sodium-to-potassium (Na/K) ratio for Japanese populations [3]. The Na/K ratio, derived from the sodium and potassium levels in spot urine samples, is considered less invasive and imposes minimal burden on participants. As a result, the Na/K ratio is expected to be adopted as a new health-related parameter. Providing appropriate salt reduction education from a young age to establish healthy diet is crucial for preventing hypertension throughout life. Therefore, the relationship between daily eating behaviors and salt intake needs to be clarified.

Previous studies have investigated the relationship between urinary salt excretion parameters based on spot urine samples from Japanese infants using a dietary questionnaire [4–6]. These studies found that processed meat products, vegetables, fruits, and seasoning and spices were associated with salt-related parameters. However, dietary habits vary by region, making it important to understand these differences. Investigating salt-related behaviors is not easy; the salt check sheet developed by Tsuchihashi et al. has been used in clinical education and research [7]. Studies targeting children have surveyed Japanese elementary or junior high school students and reported correlations with self-reported salt intake [8]. However, research on the relationship between salt-related behaviors using a salt check sheet and urinary salt excretion parameters in early childhood is lacking. Therefore, this study aimed to elucidate salt-related behaviors and urinary salt excretion parameters by analyzing urine samples collected during annual health checkups of 4-year-old children.

This study included children who participated in health checkups for 4-year-olds conducted in Ohnan Town (population 10,163, area 419.29 km^2^ in 2020), Shimane Prefecture, Japan, between May 2022 and March 2024. The municipality invited all children residing in Ohnan Town to participate in the health checkup in the year they turned 4. Additional tests were conducted alongside the routine health checkups.

Before including the participants in the study, written and verbal explanations of the research were provided to parents or guardians, and informed assent and consent were obtained. The study protocol was approved by the Research Ethics Committee for Human Subjects of Shimane University Faculty of Human Sciences (#2019-21). All procedures were performed in accordance with the tenets of the Declaration of Helsinki.

The inclusion criteria for the study participants were as follows: (1) those undergoing health check-ups, (2) those whose parents granted consent for participation, and (3) those who completed a urine test. The exclusion criteria were as follows: (1) those whose parents refused to consent, and (2) those with kidney disease as reported by their guardians. During the survey period, 122 children were eligible for participation, and the parents of 110 (90.2%) provided consent. One child was excluded owing to the inability to collect a urine sample, resulting in a final analysis sample of 109 children (89.3%).

Spot urine samples were collected during the afternoon health checkups. The samples were sent to Healthcare Systems Co., Ltd. (Aichi, Japan) for analysis. Urinary sodium (Na, mmol/L), potassium (K, mmol/L), and creatinine (mmol/dL) levels were measured. Estimated salt excretion was calculated using the following formula proposed in a previous study [4]:

$$[eqn]$$

As sodium was measured in mEq/L and creatinine in mg/dL, creatinine values were multiplied by 10. The Na/K ratio was calculated by dividing urinary sodium concentration by urinary potassium concentration.

Salt-related behaviors were assessed using the salt check sheet [7, 9] that was completed by the parents or guardians. Sex and age in months (calculated based on the date of birth) were obtained from health checkup records. Height and weight were obtained from health checkup records. Body mass index (BMI) was calculated by dividing weight (kg) by the square of height (m^2^). BMI was categorized as thinness, healthy weight, or overweight/obesity, based on age-specific cut-off values established by the International Obesity Task Force [10].

The distribution of urinary salt excretion parameters was presented by a salt check sheet. Generalized linear models were used to examine whether each item of a salt check sheet as salt related behaviors was associated with urinary salt excretion parameters adjusted for sex, age months, BMI, and year of survey. The analysis results were presented after transforming the dependent variable using the natural logarithm. Statistical significance was set at 5%.

The characteristics of the participants and the response frequencies to the salt check sheet are shown in Supplemental Tables 1 and 2, respectively. Table 1 shows percentiles of urinary salt excretion parameters by each item of a salt check sheet. Table 2 indicates the association between each salt related behavior and urinary salt excretion parameters. Lower estimated salt excretion or Na/K ratios were observed for infrequent intake of “pickles, pickled plums, etc.” than for the intake frequency of more than twice a day. Specifically, those who consumed them once a day, two-to-three times a week, or hardly at all showed significantly lower values. Similarly, lower salt excretion or Na/K ratios were found among participants who ate noodles (e.g., udon, ramen) two or three times a week or less than once a week compared to those who consumed them almost every day. In contrast, a higher Na/K ratio was observed among those who consumed approximately half a bowl or a small portion of soup-based dishes (e.g., udon or ramen soups) than among those who consumed an entire bowl. Regarding lunch habits, individuals who did not eat out or purchase convenience-store lunches had a significantly higher Na/K ratio than those who did so almost every day.

Low-frequency intake of high-salt foods (e.g., pickles, pickled plums, and noodles such as udon or ramen) was associated with lower salt excretion and Na/K ratio. However, for soup consumption, the Na/K ratio was higher among those who consumed “About half a bowl” or “Some” than among those who consumed “An entire bowl.” Similarly, the Na/K ratio was higher among those who did not eat out or buy convenience-store bento than among those who did so almost daily.

Pickles, pickled plums, etc., and noodles such as udon and ramen are known as high-salt foods in Japan. The infrequent provision of such foods at home may contribute to reduced salt intake in young children. On the other hand, the low consumption of soups such as udon and absence of convenience store bento were associated with a high Na/K ratio. Previous studies found that processed meat products, vegetables, fruits, and seasoning and spices were associated with urinary salt excretion parameters [4–6]. However, our study focused on different factors compared to previous studies.

Although it is challenging to explain the relationship that contradicts the hypothesis, the possibility that parents’ perceptions of the amount of soup being incorrect cannot be ruled out. Particularly, the frequency of noodle consumption such as udon was associated, suggesting that there may be a lack of potassium-containing foods (i.e. vegetables and fruits) at those times. Morinaga et al. reported that vegetable or fruit consumption, which is a source of potassium, was associated with the Na/K ratio [4–6]. The questionnaire used in this study to assess salt-related behaviors has been employed in research involving elementary and junior high school students [8], and it was not originally developed to evaluate dietary behaviors in young children. This may have influenced the study results. Further investigations are needed to elucidate these findings.

This study had several limitations. First, the sample size was relatively small and limited to a single town, and this may have introduced sampling error and bias, thereby limiting the generalizability of the findings to other populations or regions. However, with a participation rate of 90.2%, the study achieved a high level of engagement from the target population, using a comprehensive survey. Secondly, the study was conducted in a single town, which may not have captured the diversity of dietary habits, environmental factors, and health conditions found in other areas. Thirdly, the cross-sectional design limited our ability to infer causality. Fourthly, the reliance on spot urine samples collected during health checkups may have introduced measurement errors, as these samples may not have accurately reflected daily urinary excretion levels. Finally, the effect of unmeasured confounding variables, such as socioeconomic status, cannot be ruled out. Our study indicated that parents’ reported salt-related behaviors influenced the estimated salt excretion and Na/K ratio in 4-year-old children.

In conclusion, the frequency of high-sodium food intake was associated with both urinary sodium excretion and the Na/K ratio. However, some unexpected associations were observed between salt-related behaviors and the Na/K ratio. Further research is needed to clarify these associations, particularly in young children, to support their application in clinical practice and public health surveys.