In this age and sex-matched case-control study, we compared nutrient intake, dietary patterns, and anthropometric indices of children with ADHD in comparison to healthy controls. The main findings of this study were that the levels of micronutrient intake such as vitamin C, vitamin B1, vitamin B2, calcium, zinc, and iron in children with ADHD were significantly lower compared to typically-developing peers.
With regard to nutrient intake and dietary patterns, although there was no significant difference between the total intake of carbohydrates and fat between the groups, consumption of simple sugars and tea was significantly higher and protein intake was significantly lower in children with ADHD compared to normal children. In the study by Ríos-Hernández et al (2017), (mean age: 9.3 ± 2.8 years; 56.7% boys) there was no significant difference in dietary caloric intakes and consumption of carbohydrate and fat between children with ADHD and normal children [20]. However, the level of simple sugars and caffeine consumption in children with ADHD was significantly higher. They also found that children with ADHD received less protein than healthy controls. It should be noted that although in their study consumption of micronutrients such as iron and zinc in the ADHD group was lower than the children in the control group, this difference was not statistically significant [20]. Furthermore, in a study by Azad Bakht et al. (2012) was found that in children with ADHD (mean age: 7 ± 2 years; 71% boys), carbohydrate intake is more than normal children. Also, vitamin C, vitamin B1, vitamin B2, calcium, zinc, and iron intakes in children with ADHD were significantly lower than healthy children; this finding is in line with our results [21]. Another relevant study in children with ADHD (mean age: 8.42 ± 1.72 years; 83.8% boys) found a series of negative correlations between ADHD symptoms and seafood and meat consumption (p = 0.006), dietary intake of zinc, protein, phosphorus, selenium, calcium, and riboflavin (p = 0.014), and the serum zinc level was negatively associated to ADHD (p = 0.003) [22].
Regarding the anthropometric indices, a non-significant difference between the arm circumference of ADHD children and normal children [23]. Another cohort study found that ADHD would not be recognized as a risk factor for significant weight rise from its normal level [24]. In our study, however, the arm circumference of children with ADHD was lower than that of normal children but this difference was not statistically significant. Different dietary patterns and socio-demographic or genetic factors may explain our novel results. In our study, in the ADHD group weight was slightly greater and height was slightly shorter compared to the control group. This caused the BMI to be significantly greater in the ADHD group. Also, abdominal circumference was significantly greater in the ADHD group. In line with our results, another study showed that the abdominal circumference and body fat percentage of non-medicated boys with ADHD was significantly higher but the height was shorter than normal peers [12]. Along with what we found in the present study, the mean height of the children in the case group (ADHD) in the study performed by Ríos Hernández et al. (2017) was shorter compared to the control group (136.5 ± 16.8 cm vs. 138.6 ± 17.3 cm; respectively). Also, the mean weight of children in the case group (ADHD) in their study was higher than the control group (38.1 ± 16.2 kg vs. 36.4 ± 14.5 kg; respectively) and there were no statistically significant differences between the two groups in these regards [20].
When it comes to height, results are also mixed. A study found that the height of non-medicated children with ADHD was significantly higher than normal children but after the beginning of pharmacotherapy, the growth velocity reduced so that those who remained on stimulant medication showed an annual growth rate about 20% less than what expected [25]. Moreover, in the two separate studies conducted by Ptacek et al. group, short height for age and sex was observed in non-medicated children with ADHD [12, 13]. In the present study, although the height of children with ADHD was slightly lower than the control group, however, the difference was not significant even after considering the impact of ADHD subtype and disorder severity. The retardation in children with ADHD is increased by age. There is no significant difference in height at an earlier age compared to normal peers, however, over the time, due to the growth retardation, the height of ADHD children remains shorter than normal children. This gap in height growth does not induce a considerable risk compared with the WHO growth charts [26].
In this line, there is still controversy in various studies over the BMI difference between children with ADHD and their normal peers. In a relevant study, the BMI of children with ADHD was 19.6 ± 3.4 while it was 18 ± 3.3 in normal peers. Statistical analysis indicated that this difference was statistically significant [20]. Contrary to the above, the Mustillo et al. (2003) indicated no significant difference in BMI between children with ADHD and normal children [24]. In our study, in line with most studies, children with ADHD were more likely to have upper BMI than normal children. With respect to waist circumference, a study showed that children with ADHD who received no medication had significantly higher waist circumference than normal children [12]. On the other hand, the same researcher showed a significant difference in growth between children with ADHD that did not receive any medications and normal children when the sample size was doubles [13]. The synthesis of the results of this work by the researcher reveals that the involvement of some anthropometric indices, and reduction in growth velocity in children with ADHD, can be one of the clinical manifestations of the disease itself and not due to the complications of medications.
Finally, we observed differences in eating behavior between ADHD children and healthy controls. Children with ADHD had significantly higher waist circumference which is the indicator of fat tissue accumulation in the abdomen. The cause of weight gain and fat accumulation in these children may be due to the association between impulsive behavior and loss of control in eating [27]. Also, according to another study, aggression and lack of attention in these children increase their appetite for food [28]. Besides, improper food patterns lead to an increase in body weight. According to the researches performed on food patterns in children with ADHD, the results indicated a high consumption of simple sugars, ready-made meals and a high-carbohydrate diet [29]. On the other hand, defects in dopaminergic pathways can be effective both in ADHD and obesity. Evidence is found in people with ADHD and obese people that genetic changes may involve in the dopaminergic regulation pathways and related systems, including melanocortin, which play role in both ADHD and obesity. Due to the low levels of dopamine neurotransmitters, serotonin, and norepinephrine in the brain that lead to mood disorders and reduced desire to engage in physical activity, these children and adolescents are prone to overweight and obesity [30]. In children with ADHD, moving skills, executive functioning, and physical fitness are significantly lower compared to normal children who may contribute to obesity [31]. Some limitations should be considered in our study. Despite the instructions and guidelines delivered to parents, studied food pattern may have missed some items, including snacks used in schools, which may children provide from school buffet. Furthermore, parents’ awareness of ADHD may affect the children’s dietary patterns.