Metabolic syndrome (MetS) is not a single disease but is characterized by a combination of risk factors, such as abdominal obesity, hyperglycemia, hypertension (HTN), and dyslipidemia. Diabetes mellitus (DM), HTN, and obesity directly affect blood vessels and synergistically increase the risk of coronary artery disease, stroke, and other vascular disorders [1,2].

The global prevalence of obesity in children and adolescents is rapidly increasing [3]. Childhood obesity increases the risk of chronic metabolic disorders such as HTN and DM, and those affected are more likely to develop MetS in adulthood [4]. Therefore, promptly detecting and managing obesity and MetS in the young is imperative.

However, research in this area is limited by ambiguous diagnostic criteria for MetS in children and adolescents. Many studies have adopted modified adult MetS diagnostic criteria, which differ and impede consistent analysis [5,6].

In 2007, the International Diabetes Federation (IDF) became the first major organization to introduce diagnostic criteria for MetS in the youth [7]. The IDF diagnostic criteria mandated the presence of abdominal obesity and the fulfillment of two out of four other criteria. A study conducted by Cho et al. [8] in 2009 based on these criteria revealed a MetS prevalence of 2.0%±0.5% among Korean youth in 2015.

Double-income households surged as more women entered the workforce. Mothers’ lifestyles significantly influence their children and adolescents. Working mothers may face challenges in precisely planning their children’s nutrition and activities. Brown et al. [9] in 2010 found a correlation between maternal work hours and difficulties in managing the diet and exercise of children, potentially contributing to increased obesity rates.

Prior research has established a link between obesity in the youth and maternal work hours. Kim et al. [10] in 2018 demonstrated that maternal work hours is correlated with the body mass index (BMI) and waist circumference (WC) of the child. Similarly, Lee and Kim [11] in 2013 found that girls aged 13–18 years had higher odds ratio (OR) of being overweight or obese when their mothers worked more than 60 hours weekly.

Although associations between childhood obesity and maternal working hours have been reported in previous studies, the relationship between MetS in youth and maternal working hours remains unexplored. Therefore, in this study, we aimed to investigate the relationship between maternal work hours and children’s susceptibility to MetS.

Table 1 presents the characteristics of the participants. The prevalence of MetS was 3.1% (78 out of 2,598). Age (years) was lower in the normal group (mean±SE, 14.33±0.06) than in the MetS group (mean±SE, 14.41±0.31); however, this difference was not significant. Maternal age (years) was higher in the control group (mean±SE, 44.34±0.12) than in the MetS group (mean±SE, 43.40±0.56), but the difference was not significant. Maternal BMI (kg/m²) was significantly lower in the normal group (mean±SE, 23.25±0.10) than in the MetS group (mean±SE, 25.45±0.61) (P<0.001). There was no significant difference in sex between the two groups; the MetS group comprised 38 males (45.9%) and 40 females (54.1%), whereas the normal group comprised 1,341 males (52.5%) and 1,179 females (47.5%). There was a significant difference in BMI percentile (P<0.001); the MetS group comprised 0 underweight (<5th percentile; 0%), 0 normal (5th–84.99th percentile; 0%), 10 overweight (85th–94.99th percentile; 13.5%), and 68 obese (≥95th percentile; 86.5%) individuals. In contrast, the normal group comprised 201 underweight (<5th percentile; 8.1%), 1,834 normal (5th–84.99th percentile; 73.1%), 242 overweight (85th–94.99th percentile; 9.0%), and 243 obese (≥95th percentile; 9.8%) participants. Household income, maternal educational level, maternal marital status, and maternal smoking status did not differ significantly between the two groups. Maternal working hours were lower in the normal group (mean±SE, 26.33±0.61) than in the MetS group (mean±SE, 29.50±2.84); however, this difference was not significant. Maternal working hours were not significantly different between the groups (P=0.087). In the MetS group, work hours were none (n=20, 26.7%), 1–19 hours (n=3, 3.1%), 20–39 hours (n=20, 26.6%), 40–52 hours (n=26, 30.0%), and ≥53 hours (n=9, 13.7%). In the normal group, work hours were none (n=690, 26.0%), 1–19 hours (n=271, 11.6%), 20–39 hours (n=601, 24.6%), 40–52 hours (n=799, 31.2%), and ≥53 hours (n=159, 6.6%).

Table 2 presents the results of the logistic regression analysis of the association between maternal work hours, MetS, and its components. In the adjusted model, the OR for high WC was 2.267 (95% CI, 1.210–4.246) among those whose mothers worked ≥53 hours than for those whose mothers did not work at all (P<0.05). In the adjusted model, the OR for MetS was 0.291 (0.086–0.988) in the group with 1–19 working hours compared with none (P<0.05). The OR for MetS with ≥53 work hours was 1.93 (95% CI, 0.68–5.49) and was not significant. Notably, trend analysis indicated a significant increase in the OR for high WC with higher maternal work hours in both the unadjusted and adjusted models (P<0.05).

Table 3 shows the associations between sex, age, household income, maternal BMI, maternal working hours, and the presence of MetS. When the maternal BMI was 25 kg/m² or higher, the adjusted OR of MetS in children was high at 2.739 (95% CI, 1.557–4.817). The probability of MetS was lower in male than in female; however, the difference was not statistically significant.

Table 4 shows the stratified analysis of the association between maternal working hours and the presence of MetS according to sex, age, maternal BMI, and household income. In female children, the OR of presence of MetS was high at 6.065 (95% CI, 1.954–18.822) when the maternal work hours were ≥53 hours with significant trend (P for trend=0.016).

In this study, we investigated the association between maternal work hours and MetS in children using the KNHANES data from 2016 to 2020. Our investigation revealed a 3.1% prevalence of MetS among the adolescents. Although the unadjusted model indicated a higher risk of MetS development in children whose mothers worked ≥53 hours weekly compared with stay-at-home mothers, this association vanished after accounting for multiple variables. Conversely, children whose mothers worked 1–19 hours a week exhibited reduced MetS risk after adjustment. Regarding specific MetS risk factors, the waist circumference of a child increased proportionally with maternal work hours compared with stay-at-home mothers. In female children, the OR for the presence of MetS tended to increase as maternal work hours increased, reaching 6.065 in children whose mothers worked ≥53 hours.

Using data from 2007 to 2018, Chae et al. [14] in 2021 reported that the prevalence of MetS increased from 1.7% to 2.2% among Korean children and adolescents. In our study, which incorporated 2016–2020 data, the prevalence reached 3.1%, likely owing to the inclusion of more recent data. Although the annual prevalence was not analyzed, the significance of our study lies in employing the IDF criteria on the latest data showing MetS growth in Korean youth, paralleling prior findings.

Mothers notably influenced their children’s behaviors, including diet, screen time, and exercise. Working mothers with less child-focused time may struggle to foster healthy habits, potentially leading to obesity and MetS. As a result, extended maternal working hours could potentially negatively affect the health of children in relation to lifestyle variables such as obesity and MetS [15,16].

Our results suggest that maternal working hours are associated with abdominal obesity in children. In line with this, North American and European research has revealed that increasing maternal work hours correspond to a child’s BMI elevation [17-19]. Gwozdz et al. [20] in 2013 investigated the association between maternal work hours and childhood obesity by measuring BMI, WC, and body fat mass and found a partial association in the European population. Cutting et al. [21] in 1999 and Heude et al. [22] in 2005 reported a stronger connection between maternal work hours and the average BMI and WC of a child in cases where mothers were overweight or obese.

For instance, Kim et al. [10] in 2018 demonstrated an association between maternal work hours and the average child BMI and WC. This association was particularly robust when mothers worked longer weekly hours, the children were overweight or obese, and the children frequently consumed EDNP (energy-dense, nutrient-poor) foods [10].

Working mothers spend less time with their children and have difficulty in overseeing their children’s daily activities [19,23]. Additionally, families tend to dine out or eat late at night when a mother works long work hours or works shifts [24]. A United Kingdom found that children of mothers who worked a regular, permanent job tended to watch TV more frequently [25]. Longer screen time (TV and computers) has been linked to a higher risk of obesity among children and adolescents [26]. Therefore, extended maternal working hours elevate the risk of obesity in children, consequently increasing the risk of MetS.

In the present study, female children with mothers working ≥53 hours weekly had a higher OR than those with stay-at-home mothers. Among all participants, children with mothers working 1–19 hours per week demonstrated a lower risk of MetS. This suggest the possible J-shape association between the maternal work hours and the presence of MetS in their children, but our sample size was limited owing to the fact that we enrolled children and adolescents who had participated in the KNHANES and defined overtime as exceeding the legal weekly work hours (53 hours). Future studies with larger sample sizes may yield more conclusive results. Kachi et al. [27] in 2021 observed that irregular maternal work schedules were significantly associated with child obesity only in the high-income group; whereas Miller and Han [28] in 2008 showed an association between mothers with irregular maternal work schedules and child obesity. The inconsistent findings might be due to variations in age distribution. Further research with a larger sample size and children whose mothers worked 1–19 hours a week is necessary.

In our analysis of the presence of MetS according to sex, age, household income, and maternal BMI, the association was more pronounced when the mother was overweight or obese. This finding is consistent with those of previous reports showing that maternal BMI is associated with MetS in children [29].

Our study had several limitations. A small MetS sample size was noted, as many participants were excluded because of missing data. Although there were 3,554 youth participants in the 5 years (2016–2020) in which the KNHANES data were obtained, many were excluded from this study owing to missing data for other study variables. Moreover, the lower prevalence of MetS in young individuals than that in adults has led to a restricted number of children and adolescents with MetS, thus constraining statistical analyses. Second, our reliance on cross-sectional KNHANES data further limited the scope. This dataset solely encompasses maternal work-hour information within the collection period, lacking insight into the duration of their employment or the age of their children when they began working. Another limitation is our inability to assess health-related habits among children and adolescents. Finally, the 2020 data may have been influenced by factors such as changes in eating habits and decreased physical activity owing to the impact of social distancing during coronavirus disease 2019 (COVID-19). However, the low prevalence of MetS in this study limits further analysis. It would be valuable to integrate data from 2020, 2021, and 2022 and compare the association between maternal working hours and the presence of MetS before and after COVID-19 as a new research topic.

In conclusion, as the mothers’ working hours increased, the likelihood of their children developing abdominal obesity increased. In female children, as the mothers’ working hours increased, the likelihood of developing MetS significantly increased. Extended maternal working hours can influence the dietary and physical activity patterns of children and adolescents. Given that the lifestyles of children and adolescents may contribute to the development of MetS, additional research and analyses are warranted.