Image copyright Getty Images Image caption Alda said it was "only a matter of time" before news of his disease emerged

US actor Alan Alda, star of M*A*S*H and The West Wing, has revealed he has Parkinson's disease.

The 82-year-old told the CBS This Morning show he was diagnosed three-and-a-half years ago but had only decided to speak about it now.

"The reason I want to talk about it in public is... I've had a full life since then," he said.

"You still have things you can do," he went on, revealing he was "taking boxing lessons three times a week."

Parkinson's is a progressive condition in which the brain becomes damaged. It can lead to tremors, difficulty moving, speech changes and eventually memory problems.

Alda is best known for playing Captain Benjamin Franklin "Hawkeye" Pierce in the TV series M*A*S*H from 1972 to 1983.

He went on to play presidential candidate Arnold Vinick in The West Wing and was Oscar nominated in 2005 for The Aviator.

Alda said he had noticed during recent interviews to promote his new podcast that he "could see [his] thumb twitch in some shots".

"I thought, it's probably only a matter of time before somebody does a story about this from a sad point of view but that's not where I am," he continued.

Image copyright Alan Alda Image caption Alda acted alongside Martin Sheen (left) and Jimmy Smits in The West Wing

Alda said he had gone to his doctor to ask for a scan because he suspected he might have the disease.

"I read an article by Jane Brody in the New York Times that indicated that if you act out your dreams, there's a good chance that might be a very early symptom where nothing else shows," he explained.

"I was having a dream that someone was attacking me and I threw a sack of potatoes at them, but what I was really doing was throwing a pillow at my wife."

He continued: "This is not to short-change people who are suffering with really severe symptoms. Symptoms can get very bad, and their families can suffer.

"But in the very beginning, to be immobilised by fear and think the worst thing has happened to you... you still have things you can do."

What is Parkinson's?

Parkinson's disease is a condition in which parts of the brain become progressively damaged over many years.

The three main symptoms of Parkinson's disease are involuntary shaking of particular parts of the body, slow movement and stiff and inflexible muscles.

A person with Parkinson's disease can also experience a wide range of other physical and psychological symptoms, including depression and anxiety, balance problems, loss of sense of smell, difficulty sleeping and memory problems.

Source: NHS

Steve Ford, CEO of Parkinson's UK, praised Alda's revelation, saying it would help to "shine a light on a condition that affects 145,000 people in the UK and more than 10 million worldwide".

"The more Parkinson's is discussed the more understanding there will be, along with the vital need to drive forward research."

Image copyright Reuters / BBC Image caption Neil Diamond and Billy Connolly both have Parkinson's disease

Actor Michael J Fox was diagnosed with young-onset Parkinson's disease in 1991, when he was 30 years old. He later set up a foundation to fund research and help find a cure.

Other celebrities to suffer from the disease include comedian Billy Connolly, who was diagnosed in 2014, and singer Neil Diamond, who announced earlier this year he would retire from touring after a recent diagnosis.

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