What did a lifetime of drug and alcohol abuse do to Shane McGowan’s body?

Rock 'n' roll and intoxicants have been inextricably linked since the genre's inception. But a fast-paced, drug-addicted lifestyle is not a recipe for longevity.

The death of Pogues singer and infamous party boy Shawn MacGowan on Thursday, at the age of just 65, is the latest victim of this phenomenon.

The Irish punk rocker had suffered a serious brain infection last year, which slowly robbed him of his independence.

But the musician – who famously had crooked, rotten teeth – is no stranger to poor health.

In fact, MacGowan has spent most of his adult life battling one ailment or another resulting from chronic substance abuse.

Over the years, he has often been depicted drunkenly stumbling out of bars and slurring words in interviews – or misremembering his lyrics.

When he was five, Mr MacGowan drank two beers before going to bed. Three years later he was introduced to whisky. According to neuroscientists, early exposure to alcohol permanently rewires circuits in the brain

On one occasion he allegedly took 100 acid tablets and then ate a Beach Boys record, causing his mouth to bleed profusely.

In 2000, MacGowan spent several months in rehab for heroin addiction.

The tragedy that marred his life is perhaps not surprising, as he was introduced to Guinness by his parents at the age of five.

An uncle gave him whiskey at the age of eight. And the New York fairytale singer checked into rehab for the first time after overusing a mixture of drugs at the age of 17.

But what happens in the body when it is exposed to toxic substances for so long and in such large volumes?

We put the question to top experts in a quest to understand whether MacGowan's health was doomed before he left high school.

First and foremost, experts say using substances for such long periods of time – despite numerous health problems – is evidence that MacGowan suffered from a substance abuse disorder.

Born to Irish parents, MacGowan became involved in the burgeoning punk movement in England in the 1970s

Born to Irish parents, MacGowan became involved in the burgeoning punk movement in England in the 1970s

Dr. Erin Calipari, a pharmacologist and addiction researcher at Vanderbilt University, told DailyMail.com: 'We see this all the time, we say, you almost died, why would you do this again? But that's the disorder.

She added: “They have these experiences, but they don't change their behavior in the same way you or I would. And that's why it's so difficult to treat.”

In a 2001 interview, MacGowan said his family believed that exposing children to alcohol early would reduce the risk of them becoming too dependent on booze later in life.

“All the kids who weren't allowed to drink turned into raging alcoholics,” he told the newspaper Guardian.

Medical research says otherwise. Research shows that adolescents who start drinking before the age of 15 are four times more likely to develop an alcohol addiction during their lifetime than those who start drinking after the age of 20.

The developing brain is acutely sensitive to the effects of alcohol.

Young brains undergo significant structural changes in response to experience in a way that older brains do not.

This is called brain plasticity and explains why children and teenagers are more vulnerable to the short- and long-term effects of alcohol than adults.

Dr. Calipari said, “The developmental period is a very plastic time, meaning things can change very easily.

'But once you get past that period, the cells in your brain can change more subtly and are no longer as adaptive.'

Essentially, there is a crucial window in which the brain can change – and after this time the structures remain largely fixed.

“Changing the brain's wiring with alcohol and drugs at that age changes the way your brain helps you make decisions.”

Drinking bottle after bottle for 60 years straight would almost certainly have changed Mr MacGowan's brain structure and volume.

Dr. Calipari said: 'Brain scans of people who have been drinking for a long time show that the size of the brain is significantly reduced, compared to that of others.

“It's not something that just grows back.”

Chronic alcohol use interrupts the normal functioning of the dopamine reward pathway in the brain.

The chemical also regulates motivation and positive reinforcement.

Dr. Calipari added, “People think of it as a reward molecule, but it's actually a little more complicated than that.”

The feeling of pleasure that accompanies the release of dopamine is the brain's way of identifying and reinforcing helpful, healthy behaviors, such as eating delicious food, having sex, exercising well, and being social with friends.

But addictive drugs have a more powerful reward effect. Experts liken the difference to hearing a scream bellow through a microphone, as opposed to a soft whisper.

It often also makes someone want more of the good they have.

Chronic drug and alcohol use can cause the brain to adapt to the increased levels of dopamine.

As a result, it reduces the natural amount of the substance produced, resulting in feelings of depression, anxiety and hopelessness, as well as movement problems.

In the late 1970s, MacGowan was photographed at a Clash concert kissing his girlfriend.  When they were pulled apart, she had bitten his earlobe and his face was smeared with blood.

In the late 1970s, MacGowan was photographed at a Clash concert kissing his girlfriend. When they were pulled apart, she had bitten his earlobe and his face was smeared with blood.

A dopamine deficiency also robs a person of their ability to recognize and think through the negative consequences of their drinking or drug use. All that matters is getting that next dopamine boost.

Dr. Calipari added, “And so what you get is this kind of lack of dynamic decision-making, which influences all of your behavior toward obtaining and taking the medications.”

In his later years, MacGowan's physical health took a nosedive. He had gastroenteritis in 2012, and a bad fall while dancing and reportedly drunk in 2015 left him with a broken pelvis, and he was confined to a wheelchair. H

Dr. Calipari said, “Alcohol affects nutrient absorption, your gut microbiome, and these things affect your bones, your muscles, and your metabolism.

“And so all of those things can change your overall health.”

Chronic alcoholism is known to break down Bone mineral densitymaking osteoporosis and fractures more likely.

Alcoholism also causes disruptions of the endocrine systemincluding increased levels of the stress hormone cortisol, a reduction in testosterone and a dysfunctional thyroid gland.

It is also known that alcohol can severely hinder immune system of the drinkermaking them more vulnerable to infections.

Chronic alcoholism can lead to fatty liver disease or the accumulation of fat cells in the liver, alcoholic hepatitis, cirrhosis and liver cancer.

His latest health battle involved viral encephalitis, or inflammation and swelling in the brain that can be life-threatening.

There may not be a direct link between alcohol and drug addiction and viral encephalitis, but a weakened immune system caused by years of substance use may have increased his risk.

He was diagnosed almost a year ago and was in and out of hospital in Dublin for treatment before being discharged last week, ahead of his upcoming birthday on Christmas Day.