To investigate associations between mothers' employment (full, part time and no employment) and nutrition habits (regularity of breakfast, snack, dinner, meal speed and portion size) in a sample of Japanese junior high schoolchildren, 12–13 years of age.
A total of 10 453 children aged 12–13 years from the Toyama birth cohort study (fourth phase) participated, of whom 8906 children (89% response rate) responded to all questions related to the examined variables. Nutrition habits consisted of breakfast, snack, dinner, meal speed and meal portion. Children's obesity/overweight was measured by body mass index (BMI).
Fathers' employment had no effect on their children's nutrition patterns. Children of full-time employed mothers were the most likely to snack and to skip dinner. Children of part-time employed mothers ate larger meal portions, and those of non-employed mothers reported faster meal speeds. BMI was significantly (P<0.001) higher among children of full-time employed mothers (19.3), and lowest among non-employed mothers (19.00). Children of full-time employed mothers are more likely to be overweight, but not obese compared with other children.
There was a strong relationship between mother's employment and nutrition patterns in this cohort of Japanese schoolchildren; special programs focused on children's nutrition patterns should take into account the mothers' employment status.
Nutrition patterns are influenced by a wide range of family-related factors such as family composition, parental socioeconomic positions and age. As children's lifestyle habits and health behaviors are established within the familial context, family-related factors are crucial in interventions aimed at promoting child health. Among such factors, parental employment can be considered as one of the most important.
In Japan, as in other industrialized countries, an increasing number of mothers are engaged in the labor force market. The number of working women has increased from 15.5 million in 1985 to 20.1 million in 1993 and 27.6 million in 1997.1 During the same years, women made up to 36, 39 and 41% of the total labor force. More than 60% of the rise is because of to an increase in part-time employment.2 The increasing participation of women in the labor force has led to concerns about the health of children, especially in terms of increasing child obesity.3 The findings on the associations between maternal employment and children's nutrition patterns are inconsistent. Some studies have reported a causal association between mother's employment and child obesity in Canadian4 and American children5 Meals were less frequent when mothers were employed in a Spanish study.6 There was a higher incidence of child obesity among full-time employed Japanese mothers compared with non-employed mothers,7 Other studies do not find any relationship between employment and non-employment8, 9 or report mixed10 or no association between variation of dietary variables and maternal employment.11 Takahashi et al.12 found a positive relationship between mothers' employment and children's probability of being overweight. Similarly, Anderson et al.13 reported an association between children being overweight and long working hours for mothers. The mother's ability to supervise the child's nutrition intake and energy expenditure could be one of the explanations of this relationship. However, the relationship between mother's employment and nutrition patterns appears to be different in different social, cultural and national contexts.
The purpose of this study was to examine the relationship between nutrition patterns and mother's employment in a sample of Japanese junior high schoolchildren. We hypothesized that a full-time mother's employment is reflected in unhealthier children's nutrition patterns in terms of the timing, frequency, amount and type of food consumed by children. We also examined the association between mothers' employment and child overweight/obesity.
Data are derived from the Toyama birth cohort study, a longitudinal ongoing follow-up survey of health and lifestyle habits and child development in Toyama, western Japan, in June/July 2002. Children, (N=10 453, aged 12–13 years, response rate 93% (N=9718)) completed a lifestyle habits questionnaire in the school or home settings. In total, 8906 children (89%) responded to all questions examined in this study. The cohort children have been followed up every 3 years since the study started. In June/July 2002, the fourth phase of the survey was conducted when respondents were first junior highschool grade.
Nutrition patterns were assessed using the questions: During schooldays, do you eat your breakfast/snack/dinner with four response categories: everyday, almost everyday, almost never, never. Also, we assessed meal speed and amount with four response categories, starting from the fast/big, slightly fast/big, usual and finishing with slow/small, respectively (see Appendix). Daily and almost daily, as well as slightly fast/big and usual reply categories, were grouped into ‘regular’ and almost never, never, as well as fast/big and slow/small into ‘irregular,’ respectively. These nutritional questions have been validated.14, 15
Mother's employment was classified into full-time, part-time and non-employed. In contrast with Western countries, the age distribution of the female labor-force participation in Japan reflects the so-called <M-curve>.16 There is a 73% participation rate in 1997 among 20- to 25-year-old women. The bottom of the M curve is the 30–35 age group, with a 56% labor-force participation rate, caused by raising children. The second peak in the M curve occurs when women return to work after raising children or after children start going to school. Women in the 45–49 age group have a 72% labor-force participation rate. As nearly all fathers are full-time employed (99%), father's employment has no effect on children's lifestyle, so we did not include it in our analyses. Confounders such as body mass index (BMI), children's self-reported physical activity (measured in hours per week) and TV watching time and room tenure (a measure of children's socioeconomic position) were included in the analyses.
In our questionnaire, we asked children to report height and weight according to the record of the latest physical examination, which is conducted at least once every 4 months, when school nurses measured the height and weight of the children according to the established procedure. On the basis of these data, BMI was calculated and its distribution was stratified according to age and sex. Obesity and overweight was defined according to international rules17 as follows: overweight 21.56 and 22.14 and obesity 26.43 and 27.27 for boys and girls, respectively.
The outcome variables were children's nutrition patterns and overweight/obesity. To assess the relationship between nutrition patterns and correlated factors, t-test and χ2 analyses (or Fisher's exact test when appropriate) were performed. Binominal logistic regression analyses were used to obtain odds ratios (OR) and their 95% confidence intervals (95% CI) of the effect of mother's employment on nutrition habits and obesity/overweight, adjusted for potential confounders. Goodness of fit was assessed by the Hosmer–Lemeshow test. We also performed the Sobel mediation test18 to investigate whether the association between mother's employment and children's BMI was mediated by children's nutrition habits. Statistical level for significance was set at 0.01. Statistical analyses were performed by SPSS (10.0J) (SPSS Inc., Chicago, IL, USA).
Descriptive statistics for nutrition patterns are presented in Tables 1 and 2 . With regard to parents' employment, 98.5% of all fathers were full-time employed, 0.5 % part time and 1.0% non-employed. In the case of mothers, 50.7% were full-time employed, 32.7% part time and 16.6% non-employed.
Mothers' employment has no effect on breakfast (see Table 3 ). However, an association between mother's employment and other aspects of children's nutrition patterns can be observed. Children of part-time and non-employed mothers were more likely to snack less (OR 0.85, P=0.001 and OR 0.89, P=0.047, respectively) in comparison with children of full-time mothers. In terms of differences between children in regular dinner patterns, children of part-time employed mothers were more likely (OR 1.25, P<0.001) to eat dinner regularly compared with children of full-time employed mothers. Children of non-employed mothers were more likely to eat faster (OR 1.17, P=0.02) compared with children of full-time employed mothers. Children of part-time mothers were more likely (OR 1.13, P=0.022) to eat larger meal portions compared with children of full-time employed mothers.
We found an association between children's BMI and mother's type of employment. The highest mean BMI 19.30 (±3.0) was among children with full-time employed mothers, followed by children with part-time employed mothers 19.06 (±3.0) and then by children with non-employed mothers part-time and 19.00 (±2.9) in no employment (all P<0.001) (see Figure 1). We also examined the association between mother's employment status and children's overweight/obesity (see Table 4 ). Children of full-time employed mothers were more likely to be overweight compared with children of part-time employed mothers. The ORs remained significantly different even after adjustment for potential confounders such as sex, breakfast, snack, dinner, physical activity, TV watching time and children's room tenure.
We also looked at whether children's nutrition habits mediated the association between mother's employment status and children's BMI. Using the Sobel test for mediation, we found significant differences (P<0.01), providing evidence that poor nutritional habits in terms of snacking, skipping dinner and eating large meals mediated some of the associations between mother's employment status and children's BMI.
The relationship between BMI, nutrition patterns and overweight/obesity is presented in Table 5 . BMI was significantly higher in children who have irregular breakfast, snack and dinner, as well as fast meal speed and large portion size. Similarly, overweight was significant related with irregular breakfast, snack, dinner, eating fast and large portion size. For obesity, significant relationship was found only for meal fast speed and large portion size.
This study provides evidence of an association between mother's employment status and children's nutrition patterns in Japan. Children of full-time employed mothers were more likely to be overweight, snack regularly and skip dinner. Children of part-time and non-employed mothers were at lower risk of being overweight, although they were also associated with some unhealthy nutrition habits.
We did not find any association between mother's employment status and breakfast nutrition patterns. It is possible that in the morning all mothers try to feed their children, irrespective of their employment status. In our sample, three generation families were common, implying that other family members could supervise breakfast intake. Furthermore, in non-metropolitan areas (such as Toyama), breakfast is regarded as a very important pattern.19 Later employment start time for mothers also allows them to control children's breakfast intake.19 Similar results have been reported in French schoolchildren, where 97% reported breakfast intake.20 By contrast, Sakuma et al.21 found that children belonging to nuclear families whose mothers were less than 40 years of age and were employed did not eat breakfast. However, their sample characteristics were different in respect of age (first and six grade elementary school pupils), demography and social characteristics, and the outcome of the study was the health conditions of children and their mothers.
We found that children with mothers in full-time employment snacked more. This could be related to a positive family food environment, as reported by Hang et al.22 Parents limit access to unhealthy snacks, and this barrier could be diminished in families where mothers are not employed, because of the high level of disadvantages among this group.23, 24, 25 Children of full-time employed mothers were also less likely to regularly eat dinner. It is possible that time could be delayed for children of full-time employed mothers.
Some unhealthy nutrition habits were more common among children of part-time and non-employed mothers. Children of non-employed mothers ate faster compared with children of full-time employed mothers. Meal portion sizes were higher among children with part-time employed mothers compared with children of full-time employed mothers. One explanation could be rules and norms related to food / eating practices (for example, food quality, eating etiquette) as well as availability and access to various foods.26 The balance between food quality and quantity is related to socioeconomic position, employment type and lifestyle factors.27 However, socioeconomic position was not measured in this study and therefore cannot be taken into account in the analyses, because of the study design .
We found a graded association between children's BMI and mother's employment. Full-time employment was associated with higher children's BMI, and non-employment with lower BMI. Hawkins et al.3 reported that any maternal employment after the child's birth was associated with early childhood overweight among British children (OR 1.14). Children were more likely to be overweight for every 10 h a mother worked per week (OR 1.10). Our results regarding the higher probability of overweight in children of full-time employed mothers correspond with results in a large American cohort, where a child is more likely to be overweight if the mother worked more hours per week.5 It has been reported that children of higher status mothers are at particularly high risk for overweight, and an increase in mothers' working hours over the past three decades could explain the increasing prevalence of overweight among children. 21, 25 In our cohort, at the age of 3 years, the mother's job, limited playtime outdoors (1 h or less), snacking irregularity, an overweight father and mother, and overweight at birth were found to be the main factors that influenced children's obesity.3
Regardless of the employment status, we found that increased BMI and obesity is significantly correlated with irregular breakfast, snacking and dinner, as well as fast meal speed and large portion size. Obesity was correlated only with fast eating and large portion size. By supervising and paying attention to specific meal patterns, we can influence obesity and overweight development.
We hypothesize that employment status is reflected in the time spent with the child. Reduced supervision of meals intake by the full-time employed mothers may lead to meal skipping and frequent snacking among their children, because they become more autonomous in choosing their own food intake. It is also possible that working mothers have less time for preparing food, which may result in consumption of food prepared outside the home. This may, in turn, affect children's diet quality and increase overweight. We found that mother's employment is related to overweight, but not to obesity. Our findings are consistent with those of Hermannussen et al.,28 who found that the BMI of Japanese children and adolescents dramatically contrasts with the recent and historic BMI changes in the Western populations (the patterns of obesity evolution are different in Japan, which seems to be at early stage of obesity epidemy). Japanese children and adolescents may be more resistant against those environmental factors that have caused obesity in the affluent Western societies. Also, Japanese children presently have a lower prevalence of obesity in comparison with their western counterparts.29
In conclusion, this study provides consistent evidence of an association between maternal employment and unhealthy nutrition patterns among Japanese junior high schoolchildren. For many of the nutrition patterns, children with full- or part-time employed mothers presented had less healthy nutrition patterns. Strategies addressing the dietary patterns of children of full-time employed mothers should be elaborated. School-based nutrition programs could take the mother's employment into account. Understanding and taking account of these wider determinants of children's nutrition patterns is extremely important for their well-being and future development.
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Dr Alexandru Gaina was supported by a UCL BALZAN fellowship during 2008-2009.
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Gaina, A., Sekine, M., Chandola, T. et al. Mother employment status and nutritional patterns in Japanese junior high schoolchildren. Int J Obes 33, 753–757 (2009). https://doi.org/10.1038/ijo.2009.103
- nutrition habits
- mother employment
- Japanese children
- Toyama study
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