Parkinson's disease may have played a crucial role in Adolf Hitler's defeat, according to a controversial new study.

The research claims the neurological disease influenced some of the dictator's biggest decisions, making him reckless and ultimately losing World War II.

But it also goes a step further to say that Hitler's horrific and inhumane murders were also influenced by his disease, exaggerating his 'volatile temperament'.

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By the end of his life, Adolf Hitler had a pronounced tremor in his hands, particularly his left hand, which has caused a number of scientists to question whether he had the disease (right). A new study claims the neurological disease influenced some of the dictator's biggest decisions, making lose World War II

The study was led by Raghav Gupta and a team at the University of Pittsburgh and recently published in the journal World Neurosurgery.

'The possibility of Hitler suffering from Parkinson's has long been the subject of debate,' writes Gupta.

'Video evidence depicts that Hitler exhibited progressive motor function deterioration from 1933 to 1945.'

By the end of his life, Hitler had a pronounced tremor in his hands, particularly his left hand, which has caused a number of scientists to question whether he had the disease.

In the early 1900s, Friederich Lewy discovered protein deposits, now known as Lewy bodies, that disrupt the brain's normal functioning. Many brain cells of people with Parkinson's contain Lewy bodies (pictured)

WAS HITLER A DRUG ADDICT? A separate study published in 2013 also paints Hitler as a drug addict. According to National Geographic's Nazi Underworld - Hitler's Drug Use Revealed, psychiatrist Professor Nassir Ghaemi claims Hitler's drug abuse exacerbated his manic depression, reducing him to a feeble, trembling figure. 'It's not whether Hitler was an amphetamine addict or not – it's that Hitler had bipolar disorder and amphetamines made it worse,' he said. 'That is the issue. That has never been described before and that would explain a lot why Hitler changed in the late 1930s and the 1940s.' The report also state Morell injected Hitler with extracts from the prostate glands or ground testicles of young bulls to boost his libido so he could keep up with his much-younger lover. 'Morell gave Hitler a preparation called Testoviron, a kind of testosterone preparation, usually before Hitler was going to spend a night with Eva Braun,' Cambridge University historian Richard Evans said. 'Eva Braun was young and much fitter. Hitler was much older, he was lazy, he didn't take much exercise and I'm sure he asked Dr Morell to help him out before he went to bed with Braun.' Advertisement

Parkinson's can also cause a slow gait, bent posture and a dull stare, along with cognitive disorders such as a lack of imagination and a general apathy.

The researchers suggest that Hitler's condition may have led him to attack Russia prematurely in 1941, according to a report in Discover.

A previous study claimed that Hitler's decision to invade Russia, before defeating Britain on the western front, was a direct result of his failing health.

The study points to other bad decisions of Hitler's such the failure to defend Normandy in 1944, alongside keeping his forces in Stalingrad in 1942.

They say this was the result of the dictator's 'volatile temperament' which may have been aggravated by his Parkinson's.

The study also goes on to suggest that Hitler's lack of remorse and sympathy can be associated with his Parkinson's.

'Hitler's inhumane personality, marked by a true lack of sympathy and remorse, can also be ascribed to his condition, often compelling him to act in ways that we today characterise as brutal, callous, and unethical,' the authors say.

As Discover points out, the problem with this theory is that it can't explain Hitler's behaviour before 1933, as Hitler had shown signs of his destructive temperament long before that.

Dr John Murphy, executive vice president of Danbury Hospital, has previously put forward the same theory.

He argues the root cause of Hitler's Parkinson's disease may have been a condition known as Von Economo's encephalitis, which a swelling of the brain that can occur after an infection.