Tryptophan modulation in individuals with attention deficit hyperactivity disorder: a systematic review

Exercise Dependency and Overuse Injuries in Attention Deficit Hyperactivity Disorder

ABSTRACT

Attention deficit hyperactivity disorder (ADHD) is a common condition, but current medications have limitations, pushing a drive for alternative approaches. Different exercise-focused approaches have shown promise, but concern has also been raised about individuals with ADHD showing greater risk of addiction, including exercise dependency. Using an online survey, we examined current exercise practices, including exercise dependency and the presence of overuse injury, which could result from overexercising, in 114 adults with ADHD. We found that most were regularly exercising. None were classified as exercise dependent, but 38.9% were deemed symptomatic nondependent. Hyperactive-impulsive symptoms were a predictor of the level of exercise withdrawal experienced, and the co-occurrence of autism spectrum disorder was associated with greater risk of overuse injuries. The data indicate that ADHD may confer some greater risk of exercise dependency, aligning with previous studies investigating other addictions and suggesting further research is critical.

The Kynurenine Pathway in Attention-Deficit/Hyperactivity Disorder: A Systematic Review and Meta-Analysis of Blood Concentrations of Tryptophan and Its Catabolites

Preliminary evidence shows that the kynurenine pathway (KP) may be altered in attention-deficit/hyperactivity disorder (ADHD). We thus conducted a systematic review and meta-analysis exploring the peripheral blood concentrations of tryptophan catabolites (TRYCATs) in people with ADHD. We searched the main electronic databases up to 7th December 2023. Standardised mean differences (SMDs) with 95% confidence intervals (95%CIs) were used to compare TRYCAT concentrations between participants with ADHD and healthy controls (HCs). We included eight studies. Random-effects meta-analyses found higher kynurenine (SMD = 0.56; 95%CI: 0.04 to 1.08; p = 0.033; I2 = 90.3%) and lower kynurenic acid (SMD = -0.33; 95%CI: -0.49 to -0.17; p < 0.001; I2 = 0%) concentrations in people with ADHD compared to HCs. Additional analyses on drug-free children with ADHD showed higher tryptophan (SMD = 0.31; 95%CI: 0.11 to 0.50; p = 0.002; I2 = 0%) and kynurenine (SMD = 0.74; 95%CI: 0.30 to 1.17; p < 0.001; I2 = 76.5%), as well as lower kynurenic acid (SMD = -0.37; 95%CI: -0.59 to -0.15; p < 0.001; I2 = 0%) blood levels, as compared to HCs. Despite some limitations, our work provides preliminary evidence on KP alterations in ADHD that may suggest decreased neuroprotection. Further research is needed to clarify the role of the KP in ADHD.

The Effects of Different Exercise Approaches on Attention Deficit Hyperactivity Disorder in Adults: A Randomised Controlled Trial

Attention deficit hyperactivity disorder (ADHD) results in significant functional impairment. Current treatments, particularly for adults, are limited. Previous research indicates that exercise may offer an alternative approach to managing ADHD, but research into different types of exercise and adult populations is limited. The aim of this study was to examine the effects of acute exercise (aerobic cycling vs mind-body yoga exercises) on symptoms of ADHD in adults. Adults with ADHD (N = 82) and controls (N = 77) were randomly allocated to 10 min of aerobic (cycling) or mind-body (Hatha yoga) exercise. Immediately before and after exercise, participants completed the Test of Variables of Attention task, Delay Discounting Task, and Iowa Gambling Task to measure attention and impulsivity. Actigraphy measured movement frequency and intensity. Both groups showed improved temporal impulsivity post-exercise, with cycling beneficial to all, whilst yoga only benefited those with ADHD. There were no effects of exercise on attention, cognitive or motor impulsivity, or movement in those with ADHD. Exercise reduced attention and increased movement in controls. Exercise can improve temporal impulsivity in adult ADHD but did not improve other symptoms and worsened some aspects of performance in controls. Exercise interventions should be further investigated.

Mindfulness Interventions for Attention Deficit Hyperactivity Disorder: A Systematic Review and Meta-Analysis

Attention Deficit Hyperactivity Disorder (ADHD) is a common neurodevelopmental condition impacting children and adults. Current treatments are limited and there is increasing interest in the use of mindfulness, which is growing in popularity. Previous systematic reviews have typically focused on specific ages, outcome measures or interventions. The current review aimed to take a more comprehensive approach. Title and abstract searches were performed in five databases for randomized and non-randomized controlled trials or pre-post studies with participants with an ADHD diagnosis or a score above a clinically relevant cut-off on a validated ADHD measure. Studies had to measure symptoms of ADHD, global or social functioning. Extraction of key information including participant status (i.e., diagnosis, scale scores, comorbidities, medication use), study design, and outcome measures was conducted. Effect sizes (Hedge’s g) were calculated and where a measure had been used in at least three studies with the same population, meta-analyses were considered. Twenty-nine studies were initially identified, with seven deemed poor quality and removed from further analysis leaving, 22 studies containing data from 1237 children and adults with ADHD along with data from 525 family members. The data indicate possible benefits of mindfulness on self-compassion, quality of life, wellbeing, depression, and anxiety. The findings also suggest that mindfulness may also improve ADHD symptoms, executive function, problematic behaviours, and emotional dysregulation, although results vary by age of patient and measures used. Parent stress and parenting style have received limited attention, highlighting the need for more studies in these areas. Whilst the data presented suggest that mindfulness may be beneficial, the evidence base is not as strong as the popularity of the approach. Many of the studies lacked blind assessment, adequate randomization, or suitable control conditions. As such high-quality controlled studies considering medication, other psychosocial interventions, use of active and in active controls and comorbidity as well as longer follow-up periods, are needed to confirm this.

The Role of Tryptophan Metabolites in Neuropsychiatric Disorders

In recent decades, neuropsychiatric disorders such as major depressive disorder, schizophrenia, bipolar, etc., have become a global health concern, causing various detrimental influences on patients. Tryptophan is an important amino acid that plays an indisputable role in several physiological processes, including neuronal function and immunity. Tryptophan’s metabolism process in the human body occurs using different pathways, including the kynurenine and serotonin pathways. Furthermore, other biologically active components, such as serotonin, melatonin, and niacin, are by-products of Tryptophan pathways. Current evidence suggests that a functional imbalance in the synthesis of Tryptophan metabolites causes the appearance of pathophysiologic mechanisms that leads to various neuropsychiatric diseases. This review summarizes the pharmacological influences of tryptophan and its metabolites on the development of neuropsychiatric disorders. In addition, tryptophan and its metabolites quantification following the neurotransmitters precursor are highlighted. Eventually, the efficiency of various biomarkers such as inflammatory, protein, electrophysiological, genetic, and proteomic biomarkers in the diagnosis/treatment of neuropsychiatric disorders was discussed to understand the biomarker application in the detection/treatment of various diseases.