Disgraced NFL player Johnny Manziel has sparked a discussion about the causes of mental illness after revealing he suffers from bipolar disorder.
Manziel, 25, disclosed his diagnosis in an interview with Good Morning America on Monday, after years of controversy involving alcoholism, drug-taking and domestic violence allegations that drove him out of the league.
Now, he says he has ditched alcohol, is taking medication, and his main aim is to get back onto the football field.
But aside from his career aspirations, his interview has triggered another debate: could his illness be linked to his partying or even to his trade of injury-inducing tackles?
While many believe it has links to genetics, one landmark paper published in 2014 by Danish researchers offered the first suggestion that repetitive brain injuries – like those endured in American football – increase the risk of mental illness.
Johnny Manziel, 25, told Good Morning America that he has been diagnosed with bipolar disorder, after years of controversy involving alcoholism, drug-taking and domestic violence allegations that drove him out of the league. Pictured: Manziel in one of his final games for the Cleveland Browns in 2015
There is no clear understanding on what causes bipolar disorder, once known as manic depressive disorder, which triggers extreme highs and lows of euphoria and depression.
Most sufferers are not diagnosed until their late teens or early 20s, and their symptoms can be wildly different from one another. In some, episodes can happen daily, in others it happens every other week, or a couple of times a year.
What are the ’causes’ of bipolar, according to science?
In terms of the root cause, it is widely held that there is no one thing that ‘creates’ bipolar disorder, rather it is a combination of factors. These include:
The strongest driving factor, according to research thus far, is genetics.
Those who have a relative with bipolar are more likely to develop the condition.
This theory was strengthened by a UCLA study, published last week in the journal Science, which found that the illness shares physical characteristics with schizophrenia and autism at the molecular level.
The researchers pointed to key distinctions in the disorders’ gene expression.
‘These findings provide a molecular, pathological signature of these disorders, which is a large step forward,’ said senior author Daniel Geschwind, director of the UCLA Center for Autism Research and Treatment. ‘The major challenge now is to understand how these changes arose.’
The research was hailed as one of the clearest indicators that bipolar disorder is present from birth and has physical manifestations, despite most psychiatric illnesses being diagnosed using behavioral factors.
2. Hormonal imbalances
There is evidence that women are more likely than men to experience a phenomenon known as ‘rapid cycling’ bipolar, which is typified by four or more episodes within one year.
That has led researchers to believe there is a hormonal connection to bipolar.
However, others have argued that those with hormonal imbalances are rather experiencing a hormonal condition, and bipolar disorder is something entirely different, even if the symptoms are similar.
3. Head clashes and alcohol abuse
There is a school of thought that the chemical changes in the brain that lead to bipolar disorder are driven by environmental factors including mental stress, abuse, and alcohol abuse.
One of the most often-cited studies for this argument was a 2014 paper, which found a connection between head injury and mental illness.
The study by the University of Copenhagen, published in the American Journal of Psychiatry in 2014, studied 113,906 people over a period of 23 years after they had been hospitalized with a head injury.
Getting treatment: Manziel (pictured in his GMA interview) says he has ditched alcohol, is taking medication, and his main aim is to get back onto the football field
Lead author Sonja Orlovska found that all of them had a higher risk of developing psychiatric illnesses – 65 percent more than the general public for schizophrenia and 59 percent more for depression.
The risk was highest for those who had sustained head injuries when they were children or in their early teens.
This was true even after controlling for other factors, and they concluded that it was largely to do with damage to the blood brain barrier.
Does this relate to the CTE saga?
Ultimately, research connecting head hits to bipolar is thin, while there is unequivocal evidence that repeated head trauma increases one’s risk of CTE.
Amid the booming field of research into football-related brain injuries, there is no direct link between football and stand-alone mental illnesses.
Many former players have been diagnosed with, or are at risk of, severe neurodegenerative diseases, including CTE, ALS, and Alzheimer’s. These can drive sufferers to develop depression or other psychiatric disorders. Certain illnesses like depression can also come on in former players as their high-powered career fades.
Bipolar disorder, however, is very different chemically to depression.
The vast majority of people in the Danish study tying head injury to psychiatric illness had suffered one traumatic brain injury, and not repeated sub-concussive head hits like those suffered by football players.
However, Orlovska’s analysis of the blood brain barrier deals with the same chemical issues as the research papers from Boston University’s CTE research program, which is investigating how football-related head injuries could lead to long-term neurodegenerative diseases.
Researchers have found scores of players are at risk of life-threatening brain diseases as a result of tackling, particularly if they were subjected to head hits when they were children or young teens.