Background
Attention-deficit and Hyperactivity Disorder (ADHD) is a common neurodevelopmental disorder of childhood and adolescence [
1] marked with core symptoms of inattention and hyperactivity [
2] and cognitive dysfunctions (e.g., working memory, inhibition control) [
3,
4] with a well-documented underlying pathophysiology in the brain [
5]. There is a consensus that the etiology of ADHD is heterogeneous and results from a complex interaction of pathophysiological and neurochemical systems with genetic phenotype. Other factors that contribute to the onset or sustainability of ADHD symptoms include psychosocial, environmental, and dietary factors [
6‐
8]. The symptoms of inattention, impulsivity, and poor planning are suggested to contribute to poor health behaviors in ADHD patients [
9]. Considering such diverse etiological factors, alternative or nonmedical treatments have been also proposed for the treatment or alleviation of ADHD symptoms including several kinds of dietary interventions [
10]. In this line, however, there is still an urgent need for studies investigating dietary-related factors between ADHD children and their typically developing peers.
One factor related to dietary behavior is anthropometric indices. The word anthropometry consists of two parts: the
anthropus means the human and the
metric means measuring and is referred to as the measurement of human physical indices. One of the aims of anthropometric measurements is to examine the human body size and shape. In the developing population including children and adolescents, anthropometric measurements are applied as variables of growth and development [
11]. Other anthropometric variables including body weight, height, body mass index (BMI), skinfold thickness, peripheral measurements and measuring fat mass, and muscle mass are usually used for nutritional evaluations [
12].
Some of these anthropometric variables are investigated in children with ADHD. A study in this respect investigated the changes in body and hormone levels in children with ADHD and found that several variables are either lower or higher in children with ADHD when compared to typically-developing controls [
13,
14]. In another study, several differences in nutritional patterns were observed between children with ADHD and healthy controls. These differences were “not eating” breakfast, having a history of food allergies which contributed to ADHD symptoms severity, and higher intake of daily sugar in children with more severe ADHD symptoms [
15]. Another related study reported a significantly lower weight and height of children with ADHD in comparison with their peers without ADHD [
16]. In contrast, another study investigated obesity and overweight of ADHD children and found that 10–17 years old boys and 10–17 years old girls with ADHD were significantly overweight than those in the control group [
17]. ADHD as a potential risk factor for obesity and overweight is supported in another study that assessed the prevalence of obesity and overweight in children with ADHD [
18].
The association of dietary behavior and ADHD symptoms is important for the well-being, general health, and development of children with ADHD, however, a limited number of studies exist in this respect. Moreover, although the above-mentioned studies provide some insight about nutrients and anthropometric variables in ADHD, no comprehensive investigation of variables is available. Finally, the mixed results from previous studies warrant further investigation in carefully-controlled case studies. Accordingly in the present study, we aimed to assess the dietary patterns, nutrient intake, and anthropometric variables in ADHD children as compared with normal children. Additionally, we assessed the anthropometric variables with regard to ADHD subtype and severity of symptoms.
Discussion
In this age and sex-matched case-control study, we compared nutrient intake, dietary patterns, and anthropometric variables of children with ADHD in comparison to healthy controls. The main findings of this study were lower levels of protein intake, higher poor dietary habits (e.g., consumption of ready-to-eat food), and lower levels of micronutrient intake such as vitamin C, vitamin B1, vitamin B2, calcium, zinc, and iron in children with ADHD compared to typically-developing peers. ADHD children had greater BMI values as well.
With regard to nutrient intake and dietary patterns, although there was no significant difference in 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. 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 intake and consumption of carbohydrate and fat between children with ADHD and normal children [
21]. 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 [
21]. 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 [
22]. 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) [
23].
In anthropometric indices, a non-significant difference was found between the arm circumference of ADHD children and normal children [
24]. Another cohort study found that ADHD is not recognized a risk factor for significant weight gain from its normal level [
25]. In our study, however, the arm circumference of children with ADHD was lower than 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 was why the BMI was significantly greater in the ADHD group. Also, the abdominal circumference was significantly higher 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 higher but the height was shorter than normal peers [
13]. Along with what we found in the present study, the mean height of ADHD children was shorter compared to the control group in the study performed by Ríos Hernández et al. (2017) (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 [
21].
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 [
26]. 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 [
13,
14]. 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 controlling for the impact of ADHD subtype and disorder severity. There is no significant difference in height at an earlier age compared to normal peers, however, over time, due to the growth retardation, the height of ADHD children remains shorter than normal children.
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 [
21]. Contrary to the above, the Mustillo et al. (2003) indicated no significant difference in BMI between children with ADHD and normal children [
25]. 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 [
13]. 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 doubled [
14]. 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. ADHD children have low self-control so they show less food abstinence when it comes to food. Especially in the consumption of fast food and high in sugar. This reduces their balance, weight, and height.
Finally, we observed differences in eating behavior between ADHD children and healthy controls. Children with ADHD had a significantly higher waist circumference which is an indicator of fat tissue accumulation in the abdomen. Weight gain and fat accumulation in ADHD may be due to the association between impulsive behavior and loss of control in eating behaviors [
27]. Furthermore, it is known that 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 studies 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]. 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]. Overall, the results of this study indicate that there is a need to intervene in the lifestyle and eating behavior of children with ADHD. One interesting point here is the potential link between poor nutritional behavior and sleep problems in ADHD. It is known that there is an association between micronutrient status including some of those that ADHD children had lower levels (e.g., Zink, magnesium, iron) and sleep patterns [
32]. On the other hand, ADHD comes with sleep difficulties and circadian problems [
33] which are easily affected by lifestyle changes including the pandemic situation [
34,
35]. Life style interventions should thus include not only eating behavior but other related factors such as sleep pattern.
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. Other limitations of this study include the small sample size. Furthermore, parents’ awareness of ADHD may affect the children’s dietary patterns. It is suggested that Martin’s anthropometric measuring instruments be used for weight measurement in future research.
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