Attention‐deficit/hyperactivity disorder symptoms and dietary habits in adulthood: A large population‐based twin study in Sweden

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DISCUSSION

In this nationwide population‐based sample of adult twins, we identified positive associations between self‐reported trait dimensions of ADHD and intake of seafood, high‐fat food, high‐sugar food, high‐protein food, and an unhealthy dietary pattern, and negative associations with consumption of fruits, vegetables, and a healthy dietary pattern. However, all of the associations are small in magnitude. These associations were stronger for inattention compared to hyperactivity/impulsivity. This pattern of associations was also reflected at the etiological level, where we found a slightly stronger genetic correlation of inattention with dietary habits than of hyperactivity/impulsivity with dietary habits. Nonshared environmental influences also contributed to the overlap between ADHD symptom dimensions and consumption of high‐sugar food and unhealthy dietary pattern. However, shared environmental influences probably contributed relatively little to the associations between ADHD symptoms and dietary habits. Our findings contribute to a better understanding of common etiological pathways between ADHD symptoms and various dietary habits.

At the phenotypic level, our results are in line with previous study from adults associating elevated levels of self‐reported ADHD symptoms with higher consumption of sweet food and lower consumption of vegetables and fruits (Weissenberger et al., 2018). However, the case–control study with 51 young adults (aged 18–25) suggested that nutrient intake was not associated with ADHD, but the conclusion was limited by the small sample size leading to low statistical power (Holton et al., 2019). Our results are also consistent with prior studies based on children and adolescents (Del‐Ponte, Quinte, Cruz, Grellert, & Santos, 2019), which may indicate that associations between ADHD symptoms and dietary habits are stable across the lifespan. We further found that all associations were consistent by age, sex, and SES. Given the chronic nature of ADHD related problems, people with ADHD are most likely exposed to unhealthy dietary factors across a substantial period of time, which may in part explain the well‐established increased risk for a variety of psychiatric and somatic morbidities (Weissenberger et al., 2017).

Our findings extend the previous literature in four important ways. First, the current study is the first to identify a dimension‐specific overlap between ADHD and different dietary habits, with a stronger correlation of inattention with dietary habits than hyperactivity/impulsivity with dietary habits. Support for a dimension specific association has also been observed for ADHD symptoms and binge‐eating behavior in adults (Capusan et al., 2017). One explanation for the minimal contribution of hyperactivity/impulsivity on dietary habits in adults is that hyperactive/impulsive symptoms tend to decrease at a higher rate with age compared with inattention symptoms (Willcutt et al., 2012). Future genomic studies on the association between ADHD and dietary habits may benefit from including information about ADHD symptom dimensions and/or subtypes.

Second, our results suggest the association between ADHD symptoms and different dietary habits is in part explained by shared genetic factors. Part of the genetic overlap may reflect genetic risk variants with general effects cutting across boundaries between neuropsychiatric traits and nutrition‐related or metabolic problems (Demontis et al., 2018; Meddens et al., 2018; Watson et al., 2019). Another more specific mechanism may involve the addictive potential of highly palatable foods (such as sweet, fatty, and salty foods). It is well established that the genetic liability of ADHD is in part shared with the genetic liability of several addiction disorders, such as alcoholism (Edwards & Kendler, 2012), pathological gambling (Comings et al., 1999), internet and videogame addiction (Weinstein & Weizman, 2012), and substance abuse (Zheng Chang, Lichtenstein, & Larsson, 2012). Our findings may therefore indicate that shared genetic factors of ADHD symptoms and dietary habits may partly reflect a common genetic pathway for different addictive behaviors. Typically, substance use disorders are explained by impulsivity (de Wit, 2009), although, in line with previous studies on other addictive behaviors (Burke, Loeber, White, Stouthamer‐Loeber, & Pardini, 2007; Wang, Yao, Zhou, Liu, & Lv, 2017) reported attention problems may potentially play a potent role more broadly in addictive behaviors beyond diet.

Third, nonshared environmental factors also contributed substantially to the overlap between ADHD symptoms and different dietary habits. Research has not previously focused on such factors and how they possibly contribute to the co‐occurrence of ADHD symptoms and different dietary habits. Some studies have reported that screen time and level of physical activity are associated with ADHD symptoms, and there is also support for a link with suggested dietary habits (Mian et al., 2019; Rios‐Hernandez, Alda, Farran‐Codina, Ferreira‐Garcia, & Izquierdo‐Pulido, 2017), but whether such factors explain the nonshared environmental overlap between ADHD symptom dimensions and dietary habits remains to investigated. Future research on nonshared environmental risk factors may not only aid in our understanding of the association between diet, ADHD and related lifestyle factors and disorders, but also help identify novel prevention and intervention target.

Fourth, although the associations between ADHD symptoms and dietary habits could be explained by common genetic or environmental determinants, the significant genetic and nonshared environmental correlations, and significant MZ twin intrapair differences also provided support for a potential causal link between inattention and dietary habits. However, due to the similarity of the etiology of the two traits, we were unable to further test the test the direction of causation in the current cross‐sectional twin data. Recently, a cohort study in Dutch children was the first to test bidirectional associations between ADHD symptoms and diets, indicating that children’s ADHD symptoms predicted poor diet in later life, but that diet quality was not an independent predictor of later ADHD symptoms (Mian et al., 2019). Therefore, future longitudinal studies (e.g., cross‐lagged models) and various study designs (e.g., Mendelian randomization) are needed to replicate this finding in children and adolescents, and to explore the directions of effect in adults.

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