To our knowledge, the present study is the first to assess the association between maternal weight at conception and DXA-measured body fat in offspring. The present population-based retrospective cohort study found that maternal weight at conception was positively associated with offspring body fat at age 11 years, and that maternal overweight status at conception might be a risk factor for excess body fat in offspring. Furthermore, ROC curve analysis showed that AUCs and 95% CIs for BMI at conception and excess fat at age 11 years were greater than 0.5, and that maternal BMI values calculated using MCHH data have the potential to distinguish between the presence and absence of excess fat in offspring at age 11 years. In Japan, the MCHH is distributed by local governments, coverage of the handbook is almost 100%, and most parents keep the handbook until their children are married [14]. At present, the MCHH program is being introduced in more than 20 countries, including both developing and developed countries [14]. Therefore, maternal BMI at conception calculated from height and weight records in the MCHH could serve as useful information that may contribute to the prevention of excess fat in offspring in mid- and late-childhood.
Recent systematic reviews and meta-analyses have identified a significant association between maternal preconception weight status and child weight [2, 3], and reported that, as compared to mothers with normal weight (18.5–24.9 kg/m2), maternal overweight status (25.0–29.9 kg/m2) and obesity (≥ 30.0 kg/m2) were associated with higher risks of overweight/obese offspring (ORs for overweight/obesity defined using WHO cutoffs in late childhood: 2.28 and 4.47 for maternal overweight status and obesity, respectively) [3]. Thus, ORs for excess body fat in the offspring of overweight mothers in the present study appeared to be larger compared with ORs for excess BMI in the offspring of overweight mothers in the previous meta-analysis. These results suggest that the use of DXA, and fat indices calculated based on it, may more clearly show the impact of a mother’s BMI at conception.
The mechanism underlying the association between maternal weight at conception and offspring body fat was not explored in the present study. However, causal effects of maternal obesity on offspring obesity, which are mediated at least partly through changes in epigenetic processes including alternations in DNA methylation in utero, have been suggested in experimental studies [26]. Initial research linking developmental influences with cardiometabolic disorders in later life focused on the effects of fetal undernutrition, while accumulating evidence indicates that exposure to maternal obesity also leads to an increased risk of disease in offspring [26]. On the other hand, the family is an important social context where children learn and adopt eating behaviors, and parents play the role of health promoters and educators in the lives of children [27]. The preconception period can be a sensitive phase in life, when health behaviors affecting diet, exercise, and obesity, along with smoking and drinking, become established [4]. A previous study reported that maternal body weight is more strongly associated with pubertal weight in offspring than birth weight or infantile weight and that the relationship between maternal pre-pregnancy weight and offspring weight strengthens as children develop [28]. These results suggest that the association between maternal weight and offspring weight in adolescence might be explained by the extrauterine nutritional environment, which is attributed to maternal lifestyle [28].
If mothers are exposed to an obesogenic environment that promotes an unhealthy lifestyle, then their children are likely to be exposed to the same obesogenic factors [2]. Indeed, a recent systematic review and meta-analysis concluded that a number of parental behaviors are strong correlates of child food consumption behavior [27]. Another systematic literature review found that there was fairly consistent evidence for the association of maternal stress with children’s lower physical activity and higher sedentary behavior [29]. Evidence for the association between parental behavior and children’s physical activity or sedentary behavior was also discussed in another systematic review [30]. These results indicate that the adverse consequences of poor nutrition combined with obesity, rife in women of reproductive age, may extend across generations [4].
Previous systematic reviews have reported that overweight status and obesity in childhood and adolescence have adverse consequences on premature mortality and physical morbidity in adulthood [31], and that prevention of childhood obesity should remain a priority for public health interventions to prevent negative health outcomes during childhood as well as reducing the burden of adult obesity [32]. The US Preventive Services Task Force recommends that clinicians screen for obesity in children and adolescents 6 years and older and offer or refer them to comprehensive, intensive behavioral interventions to promote improvements in weight status [33]. Based at least in part on this, we obtained information on excess body fat in 11-year-old children as an outcome variable in the present study.
A strength of the present study is that large-scale population-based participants were recruited from residents of a defined location. This contrasts with a recently published study which had a relatively small sample population from hospital-based recruitment [23]. A population-based sample, in contrast to a sample based on hospital recruitment [23], is the ideal setting for carrying out unbiased evaluations of relationships, not only of confounders to exposures and outcomes but also among any other variables of interest [34]. In the present study, we used a DXA instrument in a mobile test room that was brought to each elementary school in all areas of the study and obtained population-based data for body fat. In contrast, although a DXA instrument is generally available in a hospital, it is difficult to obtain population-based data in that setting. Indeed, the hospital-based study mentioned above reported a lack of DXA data for 38% of eligible offspring [23]. In addition, the sample size of the present study was sufficient for multivariate logistic regression and ROC curve analyses. The single-center study design also has advantages over a multi-center design, because there is no need for inter-center calibration of DXA measurements. Finally, the advantages of retrospective cohort studies are that exposure to risk factors is recorded before the occurrence of the outcome, and they allow for the temporal sequence of risk factors and outcomes to be assessed [35].
The present study also has potential limitations. First, study areas were not randomly selected from throughout Japan. Specifically, the source population consisted of all 5th-grade students registered at four municipal schools in Fukushima (the southernmost prefecture of the Tōhoku Region), three municipal schools in Shizuoka (located halfway between Tokyo and Osaka), and one municipal school in Hyogo (located in the Kansai Region). Since these students are not fully representative of the general population of Japanese children, caution is required when generalizing the results. However, since there are no private schools in these study areas, almost all children living in these areas are enrolled in the municipal schools targeted in this study. In addition, mean height/weight measurements of girls and boys at age 11.2 years in Japanese national surveys were 144.0 cm/37.3 kg and 142.5 cm/36.6 kg, respectively [36], and those in the present study were 143.8 cm/35.5 kg and 141.7 cm/35.2 kg, respectively, showing negligible differences in anthropometric variables between the present study population and the Japanese national population. Second, fat accumulation is strongly related to sexual maturity, especially in pubertal children. However, the sexual development status of participants was not taken into account in the present study. Third, we did not have information on various parameters that could influence body composition, including the number of births experienced, paternal BMI, family income, and parental education.
Maternal weight at conception was positively associated with offspring body fat at age 11 years in Japan. Overweight status at conception might be a risk factor for excess body fat in offspring. In addition, ROC curve analysis showed that maternal BMI values calculated using MCHH data have the potential to distinguish between the presence and absence of excess fat in offspring in mid- and late-childhood. Maternal weight records thus could serve as useful information that may contribute to the prevention of excess fat in the next generation.
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