Trajectories of body mass index across the lifecourse and associations with post-menopausal breast cancer by estrogen receptor status.

BACKGROUND: Associations between a high body mass index (BMI) at single timepoints during child- and adulthood and risks of post-menopausal breast cancer are well-established, but associations with BMI across the lifecourse remains largely unknown. Therefore, we examined whether lifecourse BMI trajectories were associated with risks of post-menopausal breast cancer overall and by estrogen receptor (ER) status. METHODS: We included 6698 Danish women born 1930-1946. Information on BMI at ages 6-15 years came from the Copenhagen School Health Records Register, and information on BMI at ages 20, 30, 40, 50 and/or 50-64 years came from the Diet, Cancer and Health cohort. Breast cancer cases (n = 577) were identified in the Danish Breast Cancer Cooperative Group database. Six BMI trajectories were identified using latent class trajectory modelling. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated using Cox regression models. RESULTS: Compared to women with a trajectory characterized by an average BMI gain across life, women with the two trajectories with steep increases in BMI during childhood and adolescence that thereafter largely stabilized, had lower risks of post-menopausal breast cancer and ER-positive tumors. The adjusted HRs for ER-positive tumors were 0.67 (95% CI: 0.47-0.95) and 0.68 (95% CI: 0.46-1.01), respectively. In contrast, women with a trajectory with a low gain in BMI during childhood and adolescence followed by a subsequent steep increase during adulthood, had higher risks of post-menopausal breast cancer and ER-positive tumors when compared to women with an average BMI gain. The adjusted HR for ER-positive tumors was 1.28 (95% CI: 0.98-1.67). CONCLUSIONS: Our findings suggest that the timing of excess gain in BMI across the lifecourse impacts subsequent post-menopausal breast cancer risks. Thus, the BMI development across life is likely useful in the identification of women at increased risks of post-menopausal breast cancer.

Per- and polyfluoroalkyl substances in umbilical cord serum and body mass index trajectories from birth to age 10 years: Findings from a longitudinal birth cohort (SMBCS).

BACKGROUND: Prenatal exposure to per- and polyfluoroalkyl substances (PFAS) has been linked to low birth weight but higher childhood weight and obesity. However, little is known regarding the associations between PFAS exposure and dynamic body mass index (BMI) trajectories, particularly from birth through preadolescence. OBJECTIVE: To evaluate the associations of cord serum PFAS concentrations with BMI trajectories from birth to age 10 years and longitudinal BMI in different periods. METHODS: Based on 887 mother-child pairs in the longitudinal prospective birth cohort, we measured 12 PFAS congeners in cord serum and calculated BMI with anthropometric indicators at 9 follow-up time points from birth to age 10 years. The BMI trajectories were identified using group-based trajectory model (GBTM). To estimate the associations of cord serum PFAS levels with BMI trajectories and longitudinal changes in BMI, logistic regression models, linear mixed models, Bayesian kernel machine regression, and quantile-based g-computation models (QGC) were used. RESULTS: The median concentrations of 10 PFAS congeners included in statistical analysis ranged from 0.047 to 3.623 µg/L. Two BMI trajectory classes were identified by GBTM, characterized by high group and low group. In logistic regression models, five PFAS congeners (PFBA, PFHpA, PFHxS, PFHpS, and PFDoDA) were associated with the higher probability of being in high BMI trajectory group (odds ratio, OR: 1.21 to 1.74, p < 0.05). Meanwhile, higher PFAS mixture were related to elevated odds for the high group in both BKMR models and QGC models, with PFHpA and PFHpS being the two most important drivers jointly. In the sex-stratified analysis, the positive associations remained significant exclusively among males. In the longitudinal analysis, PFUnDA and PFDoDA were associated with increased BMI from birth to age 10 years. Furthermore, PFBS and PFHpA were negatively related to BMI throughout infancy and toddlerhood (from birth to age 3 years), whereas PFDoDA confirmed a positive association with mid-childhood (from age 6 to 10 years) BMI. CONCLUSIONS: Prenatal PFAS exposure was positively associated with BMI trajectories from birth to preadolescence and longitudinal BMI in various periods. Future research could use better trajectory modeling strategies to shape more complete growth trajectories and explore the relationship between BMI trajectories and adulthood health.

Life-course social disparities in body mass index trajectories across adulthood: cohort study evidence from China health and nutrition survey.

BACKGROUND: The social disparities in obesity may originate in early life or in adulthood, and the associations of socioeconomic position (SEP) with obesity could alter over time. It is unclear how lifetime-specific and life-course SEP influence adult obesity development in China. METHODS: Based on the China Health and Nutrition Survey (CHNS), three SEP-related indicators, including the father's occupational position and the participant's education and occupational position, were obtained. The life-course socioeconomic changes and a cumulative SEP score were established to represent the life-course SEP of the participants in the study. The growth mixture modeling was used to identify BMI trajectories in adulthood. Multinomial logistic regression was adopted to assess the associations between SEP and adult BMI trajectories. RESULTS: A total of 3,138 participants were included in the study. A positive correlation was found between the paternal occupational position, the participants' occupational position, education, and obesity in males, whereas an inverse correlation was observed among females. Males who experienced social upward mobility or remained stable high SEP during the follow-up had 2.31 and 2.52-fold risks of progressive obesity compared to those with a stable-low SEP. Among females, stable high SEP in both childhood and adulthood was associated with lower risks of progressive obesity (OR = 0.63, 95% CI: 0.43-0.94). Higher risks of obesity were associated with the life-course cumulative SEP score among males, while the opposite relationship was observed among females. CONCLUSIONS: The associations between life-course SEP and BMI development trajectories differed significantly by gender. Special emphasis should be placed on males experiencing upward and stable high socioeconomic change.

Childhood body mass index trajectories and asthma and allergies: A systematic review.

BACKGROUND: Previous systematic reviews have focused on associations between single time point measures of Body Mass Index (BMI) and asthma and allergic diseases. As BMI changes dynamically during childhood, examination of associations between longitudinal trajectories in BMI and allergic diseases is needed to fully understand the nature of these relationships. OBJECTIVE: To systematically synthesise the association between BMI trajectories in childhood (0-18 years) and allergic diseases (asthma, eczema, allergic rhinitis, or food allergies outcomes). DESIGN: We conducted a systematic review following the PRISMA guidelines, and two independent reviewers assessed the study quality using the ROBINS-E and GRADE tools. A narrative synthesis was performed as the statistical heterogeneity did not allow a meta-analysis. DATA SOURCES: A search was performed on PubMed and EMBASE databases on 4th January 2023. ELIGIBILITY CRITERIA: Longitudinal cohort studies assessing the associations between childhood BMI trajectories and allergic diseases were included. RESULTS: Eleven studies met the inclusion criteria with a total of 37,690 participants between 0 and 53 years of age. Ten studies examined asthma outcomes, three assessed association with allergic rhinitis, two assessed eczema, and one assessed food allergy. High heterogeneity and high risk of bias were observed. Overall, the quality of evidence was very low. Nevertheless, two consistent findings were identified: (1) a persistently high BMI between 6 and 10 years of age may be associated with an increased risk of asthma at 18 years and (2) a rapid increase in BMI in the first 2 years of life may be associated with subsequent asthma. CONCLUSIONS: Maintaining a normal BMI trajectory during childhood may reduce the risk of asthma. Future research that adequately addresses confounding and includes longer-term follow-up is needed. Moreover, additional studies examining potential associations with eczema, food allergies, and allergic rhinitis outcomes are needed.

Body mass index trajectories and their predictors in undergraduate students from Canada: Results from the GENEiUS study.

Objective: To explore the patterns and predictors of body mass index (BMI) change among undergraduate students from Ontario (Canada). Participants: 68 undergraduate students were followed longitudinally for 3 years with anthropometric data collected bi-annually. Methods: BMI measurements were plotted to generate individual BMI trajectory curves, which were categorized, based on the observed trajectory pattern. Within and between group comparisons of BMI were conducted via nonparametric paired tests. The association of baseline BMI, sex, and ethnicity with BMI trajectory type was assessed using multinomial logistic regression. Results: Four BMI trajectory types were observed: "stable weight" (n = 15, 22.1%), "weight gain" (n = 30, 44.1%), "weight loss" (n = 12, 17.6%), and "weight cycling" (n = 11, 16.2%) trajectories. Higher baseline BMI was significantly associated with the "weight gain," "weight loss," and the "weight cycling" trajectories as compared to the "stable weight" trajectory type. Conclusions: Our findings demonstrate an association between high baseline BMI and "nonstable" subsequent BMI change patterns among Canadian students.

Associations between Body Mass Index Trajectories in the first two years of life and Allergic Rhinitis, Eczema and Food Allergy outcomes up to early adulthood.

BACKGROUND: Early life body mass index (BMI) trajectories influence the risk of asthma at 18 years of age. However, it is unclear if these are also associated with other allergic diseases. OBJECTIVES: We investigated the associations between BMI trajectories and subsequent allergic rhinitis, eczema and food sensitisation/allergies. METHODS: Parent-reported anthropometric data were collected 18 times in the first two years of life from a cohort of 620 participants in a high-risk cohort. Group-based trajectory modelling was applied to develop BMI trajectories. Associations between trajectories and allergic rhinitis, eczema and food sensitisation at 6, 12 and 18 years of age were assessed using logistic regression models. Potential effect modifications by parental allergic disease, sex and allocated infant formula were assessed. RESULTS: We identified five BMI trajectories: average, below average, persistently low, early low and catch up, and persistently high. None showed an association with allergic rhinitis. In participants with maternal allergic rhinitis, 'early-low and catch-up' (OR = 2.83;95%CI 1.34-5.96, Pint  = 0.05) and 'below average' trajectories (OR = 2.39; 1.18-7.23, Pint  = 0.02) were associated with allergic rhinitis at 18 years of age compared with the average trajectory. No associations were observed with eczema or food sensitisation. CONCLUSION: Infants with early-low and catch-up, or below average BMI growth, were at increased risk of allergic rhinitis at 18 years if they had a mother with allergic rhinitis. These results require replication, but suggest that interactions between poor intrauterine growth, failure to thrive and maternal allergies may influence the risk of allergic rhinitis.

Adult lifetime body mass index trajectories and endometrial cancer risk.

OBJECTIVE: To identify body mass index (BMI) trajectories in adult life and to examine their association with endometrial cancer (EC) risk, also exploring whether relations differ by hormonal replacement therapy use. DESIGN: Pooled analysis of two case-control studies. SETTING: Italy and Switzerland. POPULATION: A total of 458 EC cases and 782 controls. METHODS: We performed a latent class growth model to identify homogeneous BMI trajectories over six decades of age, with a polynomial function of age. Odds ratios (ORs) and the corresponding 95% CI for EC risk were derived through a multiple logistic regression model, correcting for classification error. MAIN OUTCOME MEASURES: The relation of BMI trajectories with endometrial cancer. RESULTS: We identified five BMI trajectories. Compared with women in the 'Normal weight-stable' trajectory, a reduction by about 50% in the risk of EC emerged for those in the 'Underweight increasing to normal weight' (95% CI 0.28-0.99). The 'Normal weight increasing to overweight' and the 'Overweight-stable' trajectories were associated with, respectively, an excess of 3% (95% CI 0.66-1.60) and of 71% (95% CI 1.12-2.59) in cancer risk. The OR associated to the trajectory 'Overweight increasing to obese' was 2.03 (95% CI 1.31-3.13). Stronger effects emerged among hormonal replacement therapy never users (OR 2.19 for the 'Overweight-stable' trajectory and OR 2.49 for the 'Overweight increasing to obese' trajectory). CONCLUSIONS: Our study suggests that longer exposure to overweight and obesity across a lifetime is associated with an increased risk of endometrial cancer. Weight during adulthood also appears to play an important role. TWEETABLE ABSTRACT: Longer exposure to overweight and obesity across a lifetime is associated with an increased risk of endometrial cancer.

Association between body mass index trajectories in children and adolescents of Hanzhong city of Shanxi province and subclinical renal damage in adulthood: a 30-year longitudinal follow-up study / 中华肾脏病杂志

Objective:To investigate the association between body mass index (BMI) trajectories in children and adolescents and subclinical renal damage (SRD) in adulthood.Methods:4 623 participants aged 6-18 years old were recruited from the ongoing cohort of Hanzhong adolescent hypertension study in 1987, and the subjects were followed up in 1989, 1992, 1995, 2005, 2013 and 2017, respectively. Group-based trajectory modeling was used to identify distinct BMI trajectories in longitudinal analysis. Generalized linear model was applied to examine the association between different BMI trajectories and SRD incidence in adulthood.Results:A total of 2 678 subjects from childhood to adulthood were enrolled in this study. All subjects were divided into three groups according to three distinct BMI trajectories: low-increasing BMI group ( n=1 017), moderate-increasing BMI group ( n=1 353), and high-increasing BMI group ( n=308). Over follow up for 30 years, a total of 248 participants (9.3%) developed SRD. Urinary albumin-to-creatinine ratio (uACR) in low to high-increasing BMI group was 0.9(0.6, 1.4), 1.0(0.7, 1.7), 1.6(0.8, 3.2), respectively ( P trend<0.001), and estimated glomerular filtration rate was 98.5(87.6, 111.6) , 96.2(86.4, 109.7), 95.3 (87.5, 125.0) ml·min -1·(1.73 m 2) -1, respectively ( P trend=0.025). The generalized linear model analysis showed that uACR was increased linearly from low to high-increasing BMI group [ β=3.16(95% CI 1.02-5.31), Ptrend=0.004]. There was no correlation or linear trend between BMI trajectory and estimated glomerular filtration rate [ β=-2.30(95% CI-5.18-0.57), Ptrend=0.117]. Compared with the low-increasing BMI group, the high-increasing BMI group had greater odds of experiencing SRD in adulthood after adjusting for multiple confounders such as age, gender, medical history and lifestyle ( OR=2.83, 95% CI 1.84-4.36, Ptrend<0.001). Conclusions:Higher BMI trajectorie is correlated with higher level of uACR and risk of SRD in middle age. Identifying long-term BMI trajectorie from early age may assist in predicting individuals′ renal function in later life.

Infant body mass index trajectories and asthma and lung function.

BACKGROUND: The impact of early rapid increase in body mass index (BMI) on asthma risk and subsequent lung function remains contentious, with limited prospective studies during a critical window for lung growth. OBJECTIVE: Our aim was to investigate the associations between BMI trajectories in the first 2 years of life and adolescent asthma and lung function. METHODS: Anthropometric data on 620 infants from the Melbourne Atopy Cohort Study were collected up to 18 times in the first 24 months of the study. BMI trajectories were developed by using group-based trajectory modeling. Associations between these trajectories and spirometry, fractional exhaled nitric oxide level, and current asthma status at 12 and/or 18 years of age were modeled by using multiple linear and logistic regression. RESULTS: A total of 5 BMI trajectories were identified. Compared with those children with the "average" trajectory, the children belonging to the "early-low and catch-up" and "persistently high" BMI trajectories were at higher risk of asthma at the age of 18 years (odds ratios = 2.2 [95% CI = 1.0-4.8] and 2.4 [95% CI = 1.1-5.3], respectively). These trajectories were also associated with a lower ratio of FEV1 to forced vital capacity and a higher fractional exhaled nitric oxide levels at age 18 years. In addition, children belonging to the persistently low trajectory had lower FEV1 (ß = -183.9 mL [95% CI = -340.9 to -26.9]) and forced vital capacity (ß = -207.8 mL [95% CI = -393.6 to -22.0]) values at the age of 18 years. CONCLUSION: In this cohort, the early-low and catch-up and persistently high trajectories were associated with asthma and obstructive lung function pattern in adolescence. Having a persistently low BMI at an early age was associated with a restrictive pattern. Thus, maintenance of normal growth patterns may lead to improved adolescent respiratory health.

Life-long body mass index trajectories and mortality in two generations.

PURPOSE: To identify life-long body mass index (BMI) trajectories across two related generations and estimate their associated mortality risks and population attributable deaths. METHODS: We use prospective cohort data from the Framingham Heart Study (1948-2011) original (4576 individuals, 3913 deaths) and offspring (3753 individuals, 967 deaths) cohorts and latent trajectory models to model BMI trajectories from age 31 to 80 years. Survival models are used to estimate trajectory-specific mortality risk. RESULTS: We define seven BMI trajectories among original cohort and six among offspring cohort. Among original cohort, people who are normal weight at age 31 years and gradually move to overweight status in middle or later adulthood have the lowest mortality risk even compared to those who maintain normal weight throughout adulthood, followed by overweight stable, lower level of normal weight, overweight downward, class I obese upward, and class II/III upward trajectories. Mortality risks associated with obesity trajectories have declined across cohorts, while the prevalence of high-risk trajectories has increased. CONCLUSIONS: The mortality impact of weight gain depends on an individual's BMI trajectory. Population attributable deaths associated with unhealthy weight trajectories have grown over generations because the prevalence has increased, offsetting the decline in trajectory-specific mortality risks.

Trajectories of body mass index among active-duty U.S. Army soldiers, 2011-2014.

Establishing the shape and determinants of trajectories of body mass index (BMI) among Soldiers is critical given the importance of weight management to military service requirements. To establish the shape and determinants of BMI trajectories among Soldiers, we aimed to (1) model the overall BMI trajectory of Soldiers, (2) find the most common trajectory groups among Soldiers, (3) investigate the relationship between BMI trajectories and sociodemographic and military-specific characteristics, and (4) determine if there were Soldiers with large fluctuations in BMI. The study population included all US Army Soldiers on active-duty between 2011 and 2014 who were age 17-62 (n = 827,126). With longitudinal data from the Stanford Military Data Repository, we used group-based trajectory modeling to identify the BMI trajectories of Soldiers and multinomial logistic regression to estimate associations between Soldier characteristics and trajectory membership. Four distinct BMI trajectory groups were found: increasing, decreasing, constant, and inconstant. The constant, increasing, and decreasing trajectories were similar in shape and percentage between men and women. The constant trajectory had the fewest Soldiers who exceeded weight standards or had duty limitations. The increasing trajectory was associated with marriage and fewer service years. The decreasing trajectory was associated with more service years and higher educational attainment. The inconstant trajectory differed in shape between men and women. Over 6% of men and 12% of women had fluctuations in BMI indicative of weight cycling. Understanding the characteristics associated with BMI trends may assist the Army in targeting resources aimed to improve Soldier health and combat readiness.

Social disparities in body mass index (BMI) trajectories among Chinese adults in 1991-2011.

BACKGROUND: Obesity is a serious public health problem in China. The relationship between obesity and socio-economic status (SES) is changing and affected by uncertainty, particularly, in developing countries. The sex-related differences in body mass index (BMI) trajectories are controversial and require substantial empirical data for updating and enriching. METHODS: This study examined the relationship between SES and BMI in Chinese adults from a dynamic perspective using longitudinal data (1991-2011) from the China Health and Nutrition Survey (CHNS). Then, sex-related differences were determined. A hierarchical linear model was used. RESULTS: SES positively affected the male BMI changes, with faster BMI growth rates in the high-SES males over the past 20 years. By contrast, female BMI was only affected by BMI baseline and residential area. Specifically, greater BMI baseline led to greater BMI growth rate and earlier BMI decline. In the past 20 years, the BMI growth rate has been greater in the urban females than in the rural females. CONCLUSIONS: The relationship between SES and obesity is complex in China, and a substantial sex-related difference exists. We argue that this large sex-related difference is due to the rapid economic and social changes that have affected national health and increased the gender inequality and social role restrictions in females. We provide insights for further research and policy recommendations.

Childhood adiposity trajectories are associated with late adolescent blood pressure: birth to twenty cohort.

BACKGROUND: Elevated blood pressure in childhood is a risk factor for adult hypertension which is a global health problem. Excess adiposity in childhood creates a predisposition to develop adult hypertension. Our aim was to explore distinct sex-specific adiposity trajectories from childhood to late adolescence and examined their association with blood pressure. METHODS: Latent Class Growth Mixture Modeling (LCGMM) on longitudinal data was used to derive sex-specific and distinct body mass index (BMI: kg/m(2)) trajectories. We studied 1824 black children (boys = 877, girls = 947) from the Birth to Twenty (Bt20) cohort from Soweto, South Africa, and obtained BMI measures at ages 5 through 18 years. Participants with at least two age-point BMI measures, were included in the analysis. Analysis of variance (ANOVA), chi-square test, multivariate linear and standard logistic regressions were used to test study characteristics and different associations. RESULTS: We identified three (3) and four (4) distinct BMI trajectories in boys and girls, respectively. The overall prevalence of elevated blood pressure (BP) was 34.9 % (39.4 % in boys and 30.38 % in girls). Boys and girls in the early onset obesity or overweight BMI trajectories were more likely to have higher BP values in late adolescence. Compared to those in the normal weight BMI trajectory, girls in early onset obesity trajectories had an increased risk of elevated BP with odds ratio (OR) of 2.18 (95 % confidence interval 1.31 to 4.20) and 1.95 (1.01 to 3.77). We also observed the weak association for boys in early onset overweight trajectory, (p-value = 0.18 and odds ratio of 2.39 (0.67 to 8.57)) CONCLUSIONS: Distinct weight trajectories are observed in black South African children from as early as 5 years. Early onset adiposity trajectories are associated with elevated BP in both boys and girls. It is important to consider individual patterns of early-life BMI development, so that intervention strategies can be targeted to at-risk individuals.

Variations over four decades in body mass index trajectories prior to diagnosis of diabetes mellitus: The Manitoba Follow-up Study, 1948-2007.

OBJECTIVE: The aim of the study was to explore the variations in body mass index (BMI) trajectories during the 20 years before diagnosis of type 2 diabetes mellitus (T2DM) over four decades between 1968 and 2007. METHODS: Longitudinal measurements of BMI from 437 men, all with a diagnosis of T2DM, were used in the analysis. A mixed method approach was used to fit individual patterns of BMI measurements during the 20 years before diagnosis of T2DM. RESULTS: The mean BMI at diagnosis was 26.7 kg/m2 (95% confidence interval, 26.4-27.1). Compared with men whose condition was diagnosed between 1968 and 1977, for men with a diagnosis between 1978 and 2007 the mean BMI about 10 years before diagnosis significantly increased by 0.92 to 1.54 BMI units. Decades also varied in how long there was a persistent increase in BMI during the 20 years before diagnosis. The rate of change in mean BMI among men whose T2DM was diagnosed in the most recent two decades increased by 8.8% to 22.6% during the 10-year interval before diagnosis, but there was no significant difference among men given a diagnosis between 1978 and 1987. The quadratic trend of BMI prior to diagnosis was also significantly affected by age at diagnosis. CONCLUSION: The BMI trajectories during the 20 years leading up to T2DM varied by decade of diagnosis. The increase in BMI persisted for much longer among relatively younger men with a diagnosis in more recent decades. Strategies to prevent T2DM, informed by the pattern of BMI trajectories, should be customized to consider a potential age-period effect.

Obesity and mortality risk: new findings from body mass index trajectories.

Little research has addressed the heterogeneity and mortality risk in body mass index (BMI) trajectories among older populations. Applying latent class trajectory models to 9,538 adults aged 51 to 77 years from the US Health and Retirement Study (1992-2008), we defined 6 latent BMI trajectories: normal weight downward, normal weight upward, overweight stable, overweight obesity, class I obese upward, and class II/III obese upward. Using survival analysis, we found that people in the overweight stable trajectory had the highest survival rate, followed by those in the overweight obesity, normal weight upward, class I obese upward, normal weight downward, and class II/III obese upward trajectories. The results were robust after controlling for baseline demographic and socioeconomic characteristics, smoking status, limitations in activities of daily living, a wide range of chronic illnesses, and self-rated health. Further analysis suggested that BMI trajectories were more predictive of mortality risk than was static BMI status. Using attributable risk analysis, we found that approximately 7.2% of deaths after 51 years of age among the 1931-1941 birth cohort were due to class I and class II/III obese upward trajectories. This suggests that trajectories of increasing obesity past 51 years of age pose a substantive threat to future gains in life expectancy.

Trajectories of growth in body mass index across childhood: Associations with maternal and paternal employment.

Research links mothers' employment to higher body mass index (BMI), a measure of weight-for-height, among their children. However, how maternal employment patterns relate to their children's BMI trajectories, and the role that fathers' employment plays in when and at what rate children grow, remain unclear. With data on children from 2 to 15 years of age living in two-parent families from the U.S. NICHD's Study of Early Child Care and Youth Development (N = 1107), individual growth models are used to describe American children's BMI trajectories as predicted by maternal and paternal employment characteristics. Results indicate that, by age 15, children's BMIs are, on average, nearly one-half of a standard deviation above recommended levels, and the majority of growth occurs during the preschool period. The duration of maternal employment, and combined measures of maternal and paternal employment duration, are both associated with higher child BMI across childhood. Associations are small but cumulative. Notably, the association between the duration of time children lived in dual-earner families and child BMI is larger than that between maternal employment duration alone and children's BMI, which is strongest during the preschool period. Combined measures of maternal and paternal employment intensity, defined as the number of periods both parents worked 35 or more hours per week, are associated with higher child BMI during the preschool period only. Findings highlight the importance of taking into account both parents' employment characteristics in investigating children's physical development.