This study investigated the association between ADHD and nutritional status, as well as body composition, using multiple approaches. The findings revealed that at 4 years of age, children with higher ADHD symptom scores exhibited higher z-scores for height. At ages 6–7, children with higher ADHD also demonstrated higher z-scores for BMI, weight, and height. In terms of body composition, higher ADHD symptom scores (measured at both ages 4 and 6–7 years) were associated with higher FFM and FFMI at 6–7 years of age. However, no significant associations were observed between ADHD symptoms and FM or FMI at either age. Furthermore, the CLPM analysis did not provide strong evidence of a bidirectional association between ADHD symptoms and BMI between the ages of 4 and 6–7.
Our findings reveal an association between ADHD symptoms and BMI at ages 6–7. Consistent with these results, previous studies have also documented a positive correlation between ADHD symptoms and higher BMI in children of a similar age [4, 5, 7, 9, 32]. While the increase in BMI observed in our study is modest, even slight changes during childhood are clinically significant, given the critical period for shaping body composition [33]. The literature posits several pathways linking ADHD, weight, and elevated BMI. Genetic factors, dysfunctional behaviors, and neuropsychological deficits are suggested as potential mechanisms, suggesting that symptoms of impulsivity, inattention, or hyperactivity may contribute to weight gain. Moreover, these symptoms can hinder effective BMI reduction efforts [12]. Notably, there was no association between ADHD symptoms and BMI at 4 years of age; the association emerged later, at 6–7 years.
In addition, we showed that at 6–7 years of age, the children had greater weight and height. Other studies have also found that ADHD symptoms were associated with an increase in body weight in childhood [4, 22, 34]. One plausible explanation for weight gain is the presence of impulsivity and inattention symptoms, which are intimately related to binge eating. This reinforces the hypothesis that the reward system, identified through binge eating, is a mechanism shared between ADHD and excess weight [19, 20]. There was no association between ADHD symptoms and weight at 4 years. On the other hand, an increase in height was associated with higher ADHD symptom scores at both ages. Prior studies that examined the association between ADHD and linear growth have produced inconsistent results. A recent study conducted on preschool children revealed that ADHD children with hyperactive/impulsive symptoms were taller, while children with the combined type were shorter compared to children without the disorder [35]. Other studies, available in the literature, have found reported that children with ADHD are shorter in stature [34, 36–38], while others find no association [39–43], the effect of ADHD symptoms on stature remains inconclusive.
Studies suggest that shorter height observed among children with ADHD may reflect higher levels of stressful events, leading to increased cortisol release. This hormone participates in the physiology of bone, muscle, and fat mobilization processes, as well as increasing the secretion of somatostatin, which is responsible for inhibiting the secretion of growth hormone by the pituitary gland [37]. Genetic and environmental factors are known to account for 65–85% of height variation, while environmental factors, including diet, psychosocial stress, and lifestyle, contribute an additional 5–23% [44]. Therefore, the precise mechanisms by which ADHD might influence growth are not fully understood.
When evaluating body composition, we found that at both 4 and 6–7 years of age, children with higher ADHD symptom scores have more FFM, suggesting that the increased weight and BMI scores are not due to excess FM, but rather to a greater quantity of FFM (muscle and bone tissue). These findings align with those from a study with children from the Generation R cohort [32], which also used DXA to assess body composition. The authors concluded that a higher amount of lean mass at age 6 was predictive of more severe ADHD symptoms, while a higher amount of fat at age 6 predicted lower ADHD symptoms at age 9. Additionally, they found that more severe ADHD symptoms at age 6 led to a 0.22 kg increase in fat mass at age 9, suggesting that childhood ADHD symptoms can cause both weight and FM increase [32].
Another study, carried out [22] with children aged between 4 and 6 found that higher hyperactivity/inattention scores were associated with a lower percentage of body fat, but this effect was attenuated after adjusting for physical activity. The authors suggest that the lower percentage of fat is partially explained by the higher levels of daily physical activity (performed by children with higher hyperactivity scores), since hyperactivity involves not only agitated movements, but also an increase in general motor activity, justifying the increase in FFM in these children [23]. In children and adolescents with typical development, increased physical activity (both in terms of time and intensity) is associated with lower FM and higher FFM [23, 45, 46]. However, no studies were found evaluating this relationship in children with ADHD[5].
Studies establishing reference values for body composition in children with TD indicate significant variations with advancing age, observing a higher FFM has been observed in younger children [47–49] and an increase in FM during adolescence and adulthood [47–50]. Due to the typical characteristics of children's body composition, with lower FM and higher FFM, excess adipose tissue may not influence ADHD symptoms in childhood [23], starting in adolescence and adulthood [11, 12, 14]. However, the literature presents limited evidence on the relationship between body composition and ADHD symptoms in children, demonstrating a considerable gap that requires further research.
In the present study, we utilized the cross-lagged panel model (CLPM) to understand potential bidirectionality of the association between ADHD and nutritional status. Our findings indicated that a slight increase in ADHD symptom score at age 4 predict a higher BMI/A at age 6–7. Similarly, a minor increase in the BMI/A z-score at age 4 predict a higher score on the ADHD symptom scale at age 6–7, though these results were not statistically significant. However, few studies have longitudinally assessed these two conditions to elucidate the direction of this relationship [10, 11, 22, 32, 51].
The study [32] conducted with children participating in the Generation R cohort analyzed the bidirectionality of ADHD with body composition data, also using a CLPM. The authors found no evidence that body composition at age 6 was able to predict changes in the severity of ADHD symptoms at age 9, indicating that fat mass does not appear to have a protective or prejudicial effect on the risk of ADHD in this age group [32]. Still, they found that more severe ADHD symptoms at age 6 predicted greater fat mass at age 9.
In a longitudinal study carried out in Spain with preschoolers, the influence of BMI began at 3 years of age, predicting higher ADHD scores at 4 years[9], while in a study carried out with girls in the United States, no association was found between ADHD and BMI in early childhood, only in adolescence [11], the increase in BMI was significantly throughout development, resulting in higher levels in adolescence and adulthood, with a prevalence of obesity of 40.2% in those with ADHD in contrast to only 15.4% in the comparison group [11]. These results reinforce the idea that in very young children, even though they already show an increase in body weight and BMI, its effect is still small on ADHD symptoms [2, 5, 7, 22], mainly because most of these studies do not have body composition data [22], preventing the conclusion that this increase is really due to excess FM, and not FFM, as found in our results.
Findings should be interpreted considering some study limitations. The assessment of ADHD symptoms in population-based studies differs from the gold standard for diagnosing the disorder, clinical assessment. We used data from the SDQ, a brief and validated screening tool for assessing levels of hyperactivity/inattention, with high predictive sensitivity [29]. In the analysis that investigated the association between ADHD symptoms and height, there was no adjustment for the father's height because this information was not collected. Another limitation is the lack of body composition data (DXA) at 4 years of age, which prevents us from conducting a bidirectional assessment of body composition data, in addition to BMI. In addition, at the 6–7-year follow-up, approximately 53% of the cohort were able to undergo DXA examinations due to the change at the start of the follow-up, affected by the COVID-19 pandemic, and many interviews were conducted by telephone.
As strengths of this study, we highlight the longitudinal design of the analyses, using data from a population cohort with a large sample size and high follow-up rates, where data collection was carried out by trained and standardized staff, minimizing the risk of information bias, allowing us to investigate the association between ADHD symptoms and nutritional status and body composition in childhood and explore the bidirectionality of this association. In addition, we used complex data to measure body composition, using DXA, which has so far been little explored in children with ADHD, and which is unheard of in low- and middle-income countries such as Brazil.
In conclusion, our study observed that children with higher ADHD symptom scores exhibited greater body growth (weight, height, and BMI). Analysis of body composition indicated that the increase in weight and BMI was attributable to gains in fat-free mass rather than excess fat mass. However, literature suggests that accumulation of body fat typically occurs during adolescence, implying that at ages 6–7, fat mass may not yet influence ADHD symptomatology. Given the consistent findings linking ADHD symptoms with obesity in adulthood, our study underscores the importance of promoting healthy lifestyle habits in childhood, including physical activity and a balanced diet, as part of ADHD management. Future longitudinal investigations focusing on the transition from childhood to adolescence may elucidate when the relationship between ADHD symptoms and excess fat mass begins to manifest.