Childhood adversity, encompassing experiences like economic hardship, family illness, and parental divorce, significantly impacts morbidity and mortality throughout life. Prior research suggests a link between adversity and health issues, including hospitalizations, even in childhood. Potential mechanisms involve the influence of adversity on health behaviors (diet, activity, sleep) and physiological stress responses affecting metabolism and inflammation. Childhood overweight/obesity, linked to high BMI, further increases adult morbidity/mortality risk. Childhood BMI might be a key factor linking adversity to later health, making it a potential intervention target. Existing literature presents mixed findings on the association between childhood adversity and BMI, potentially due to variations in adversity definitions, measurement methods, timeframe, and study populations. This study addresses these limitations by combining nationwide register data on childhood adversities (DANLIFE) with school health records (Copenhagen School Health Records Register, CSHRR) from a large, unselected sample of Danish children born between 1980 and 1996. The use of objective measurements from these data sources mitigates recall bias, allowing for a robust assessment of the type, level, and timing of adversity's impact on BMI in childhood and adolescence. The study focuses on BMI after the adiposity rebound (around age 6) and in adolescence, as adolescent BMI is a better predictor of adult BMI than childhood BMI.

Systematic reviews on the link between childhood adversity and childhood BMI/obesity have yielded inconsistent results. One review found no clear association between childhood maltreatment and obesity, while others suggested a positive correlation between adverse events and BMI/overweight/obesity. These inconsistencies likely stem from differences in adversity definitions, measurement techniques, study timeframes, and participant populations. The need for longitudinal studies using large, unselected samples with sound methodologies for assessing both adversity and BMI is emphasized. The type, timing, and duration of adversity exposure are crucial factors to consider. This study addresses these gaps by using a unique combination of register data and health examination data, enabling a comprehensive and objective investigation of the relationship.

This register-based study combined data from the DANLIFE cohort (covering childhood adversities for children born in Denmark between 1980 and 2015) and the CSHRR (containing health examination data, including height and weight, for Copenhagen schoolchildren born between 1930 and 1996). The study sample included 53,401 children meeting specific inclusion criteria (presence in both registers, survival beyond age 6, and available height/weight data at ages 6-7 and/or 12-15). Early childhood adversity groups were defined using group-based multi-trajectory modeling on yearly adversity counts (0-5 years) across three dimensions: material deprivation, loss/threat of loss, and family dynamics. The optimal number of groups (4-6) was determined based on interpretability and group size, resulting in five groups: low adversity, moderate material deprivation, high material deprivation, loss/threat of loss, and high adversity. BMI z-scores were calculated using age- and sex-specific reference curves generated from the CSHRR data. Structural equation modeling, stratified by sex, was used to assess direct and total associations between adversity groups and BMI z-scores in childhood and adolescence. The models adjusted for potential confounders (maternal age, parental origin, parental cardiometabolic illness, birth year) and, in additional analyses, parental education, size for gestational age, and preterm birth. The analyses employed maximum likelihood with missing values (mlmv) to handle missing data. The clinical relevance of BMI z-score differences was illustrated by comparing the weight differences between specific z-scores for children of average height at relevant ages.

Five distinct early childhood adversity groups were identified: low adversity (51%), moderate material deprivation (30%), high material deprivation (14%), loss or threat of loss (3%), and high adversity (2%). Boys and girls in the moderate or high material deprivation and loss/threat of loss groups exhibited slightly higher BMI z-scores in adolescence compared to the low adversity group. The most pronounced association was observed in girls from the loss/threat of loss group (b (95% CI) = 0.18 (0.10, 0.26)). Boys in the high adversity group had a slightly lower BMI z-score in childhood than those in the low adversity group (b (95% CI) = −0.12 (−0.22, −0.02)). The associations were generally consistent across different model adjustments (parental education, size for gestational age, preterm birth). The weight differences associated with these BMI z-score differences were relatively small (e.g., 0.8 kg for a 0.10 difference in boys at age 14, 1.5 kg for a 0.18 difference in girls at age 14), although the differences tended to increase with age. Sensitivity analyses excluding parental cardiometabolic illness yielded similar results.

This study demonstrates small but discernible associations between specific types of early childhood adversity and adolescent BMI. The findings suggest that the impact of adversity on BMI depends on the type and severity of the experiences. Material deprivation and loss/threat of loss were associated with higher BMI, while high adversity across multiple dimensions showed no clear association or even lower BMI in boys. These differences may reflect distinct physiological and psychological consequences of different adversity types. Material deprivation may limit access to healthy food and physical activity, while loss/threat of loss can significantly impact mental health and available resources. The lower BMI observed in boys in the high adversity group might be due to chronic stress and resource scarcity. Although the effect sizes were small, the potential for these differences to accumulate over time and contribute to later-life health disparities cannot be ignored. The study generally didn't find strong sex differences, although the association between loss/threat of loss and adolescent BMI was more pronounced in girls, while the association between high adversity and childhood BMI was specific to boys.

This large population-based study reveals small but significant associations between certain types of early childhood adversity and adolescent BMI. The impact varies depending on the type and severity of adversity, suggesting that different interventions may be needed to address the diverse consequences of these experiences. While childhood and adolescent BMI does not appear to be a major factor linking early adversity to later-life health, early preventative efforts focusing on mitigating childhood adversity remain essential for improving long-term health outcomes.

While the study boasts a large sample size and objective data, some limitations exist. The grouping of individuals into adversity categories inherently introduces uncertainty and may influence the detection and magnitude of effects, especially in smaller groups. Although the study included various adversity types, direct measures of violence or childhood maltreatment were unavailable. Confounding by factors like genetics or neighborhood characteristics cannot be entirely ruled out. The time lag between childhood and adolescent BMI measurements varied, which could have affected the identification of direct associations.