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Attention Deficit Hypersensitivity Disorder (ADHD) affects a person’s ability to pay attention, control impulses, or sit still for long periods of time. While it is typically associated with children, ADHD is affecting adults now more than ever before. In fact, it has more than doubled between 2007 and 2016 in adults, resulting in approximately 10.5 million American adults living with ADHD.What exactly is causing the rise? Researchers suggest that it could be related to interactions of vulnerability genes with changes in the definition of ADHD, increased technology use and alterations in the brain gut microbiome system.

Genetics

“…ADHD within families is evidenced more in biological parents of children with ADHD compared to adoptive parents of children with ADHD.”

Decades of research have shown that genes play an important role in the development of ADHD. This is especially apparent in studies conducted in families, twins, and adoptions. For example, a study of 894 individuals with ADHD and 1135 of their siblings aged 5–17 years old revealed a ninefold increased risk of ADHD in siblings when compared to controls. When looking at twin studies, ADHD tends to be a pattern as well. In a Swedish study, researchers observed ADHD in about 80% of twins, full siblings, and even half-siblings. To compare, ADHD within families is evidenced more in biological parents of children with ADHD compared to adoptive parents of children with ADHD. This was observed in a study where only six percent of adoptive parents of children with ADHD had ADHD themselves, whereas 18% of the biological parents of children with ADHD also exhibited ADHD.

Redefining ADHD

ADHD is a disorder that often goes unnoticed in children and may not be detected until adulthood. To be diagnosed with the disorder, specific symptoms must be identified by age 12, according to the latest edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM) – the guide used by physicians to diagnose and treat mental health conditions. While symptoms need to be present before the age of 12, it doesn’t necessarily mean that the condition needs to be diagnosed by that age. In some cases, symptoms may be identified by reviewing old journals or teacher’s notes, interviewing family members, or through a patient’s own recollection of childhood memories.

“…since the definition was later expanded to include symptoms associated with inattention, the disorder became more diagnosed.”

There are plenty of known ADHD symptoms to look out for in children. However, ADHD in adults may be more difficult to detect because it can manifest in different ways. Generally, adults are better at controlling their restlessness and are more disciplined with their emotions than children. Whereas a child may have a difficult time sitting still in class, an adult may feel impatient when waiting in long lines or may frequently interrupt ongoing conversations. This suggests that symptoms do not present the same way in everyone, especially across different age groups. Since ADHD was originally considered to be a hyperactive disorder in children, it is often thought that hyperactivity had to be a symptom of the disorder. However, since the definition was later expanded to include symptoms associated with inattention, the disorder became more diagnosed. It is important to note that this does not necessarily mean that it became more common. It could be that redefining ADHD is simply revealing more diagnoses that have been often overlooked in adults.

Lifestyle and diet

While genetic factors have been heavily studied, research on environmental factors is still novel but continues to reveal new findings. A recent study demonstrated that frequent use of digital media, including social media, gaming, texting, and streaming movies, music, or TV, can increase the risk of developing ADHD symptoms by almost 10 percent. Constant use of technology may lead to attention problems because it reduces the amount of time for the brain to live in a resting state. Brain imaging studies reveal that greater activity occurs in certain brain regions during resting states than during cognitive tasks. This has led researchers to hypothesize that the resting state of the brain may constitute a network that supports a ‘default mode’ of brain function. Some researchers even suggest limiting smartphone usage to 60 minutes per day – a seemingly impossible goal – to treat technology-related ADHD.

Why is ADHD becoming more common?

There are several reasons why ADHD is becoming more common in adults. While genetics play a major role in the vulnerability to the disorder, so do environmental factors such as excessive digital technology use, diet and other lifestyle factors may be behind the rapid increase in prevalence. Thankfully, there is an increased awareness of ADHD symptoms and a variety of ways to manage the disorder. Therapeutic approaches may include medication or applying behavioral and lifestyle changes. Small adjustments, like meditation or spending less screen time may be helpful for allowing the brain to rest from constant stimulation. Taking active steps throughout the day to lessen screen time, whether it be by placing the phone in a different room before going to bed, or putting time restrictions on applications, can help adults with ADHD build a healthier relationship with technology and improve their overall mental health.

“Suggestive evidence for a role of the gut microbiome in ADHD emerges from several lines of research…”

Recent research suggests that the brain-gut-microbiome system, the bidirectional communication system between the gastrointestinal tract and the central nervous system, may play a role in the pathophysiology of ADHD. Suggestive evidence for a role of the gut microbiome in ADHD emerges from several lines of research, including epidemiological studies, animal models, and human clinical studies. There have been major changes in our gut microbiome during the past 75 years, and these changes have been associated with dramatic changes in our diet.

Animal models of ADHD have provided insights into how alterations in the gut microbiome can affect behavior and neurodevelopment. For example, studies in rodents have shown that manipulating the gut microbiota can result in changes in hyperactivity and attention, further supporting a potential link between the gut microbiome and ADHD.

Some human studies have found differences in the composition of the gut microbiome between individuals with ADHD and those without. Evidence suggests that certain beneficial bacterial genera, such as Bifidobacterium and Lactobacillus, might be less abundant in individuals with ADHD. These bacteria are known for their beneficial effects on gut health and potentially on the brain via the gut-brain axis. Even though such correlational studies don’t prove causality, they suggest a possible role of relative microbial abundances and ADHD.

There is also evidence suggesting that ADHD may be associated with low-grade inflammation and alterations in immune system function. As often reviewed in this blog, the gut microbiome plays a crucial role in modulating the immune response and systemic inflammation. Dysbiosis (an imbalance in the gut microbial community) can lead to increased intestinal permeability, allowing pro-inflammatory substances to enter the bloodstream and potentially affect brain function.

“…exert several beneficial effects on gut health, but can also influence brain function and behavior…”

The gut microbiota produces SCFAs such as butyrate through the fermentation of dietary fibers. Preclinical studies have shown that butyrate not only exert several beneficial effects on gut health, but can also influence brain function and behavior, and differences in the levels of SCFAs have been observed in individuals with ADHD compared to controls. A small percentage of these compounds generated by the gut microbiota are able to cross the blood-brain barrier and may impact brain processes through central immune activation and related to attention and hyperactivity.

In summary – like in many brain disorders – there is strong evidence for an interaction between risk genes and environmental factors in the etiology of ADHD. This is particularly true for disorders with progressive increase in prevalence during the past 75 years, such as autism spectrum disorders and ADHD. The dramatic increase in prevalence of this disorder in particular in children strongly supports a prominent role of lifestyle changes, in particular the rapidly increase in the use of digital technology and possibly changes in our diet.