A “sweet and gentle” 44-year-old man with mental health conditions appears to have starved to death after his benefits were cut.

Mark Wood, of Bampton, Oxfordshire, was deemed to be fit for work, which led to his sickness and housing benefits being cut about four months before his death in August last year. This had left him with £40 a week to live on.

His family, who were unaware his benefits had been reduced, said he was a “proud” man who tried to live independently. They called for the Government to change the way people with mental health problems are treated in relation to benefits, The Guardian reported.

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Coroner Darren Salter said Mr Wood’s death was probably “caused or contributed to by Wood being markedly underweight and malnourished”, but added it was not possible to establish the cause of death conclusively.

Mr Wood weighed just 5st 8lbs — 35kg — when he died and his doctor, Nicholas Ward, said this body mass index was incompatible with life.

Dr Ward wrote a letter for Mr Wood to give to the Jobcentre, which said he was “extremely unwell and absolutely unfit for any work whatsoever”.

“Please do not stop or reduce his benefits as this will have ongoing, significant impact on his mental health. He simply is not well enough to cope with this extra stress. His mental and medical condition is extremely serious,” the letter added. It is not known if Mr Wood gave the letter to the Jobcentre.

Mr Wood’s sister, Cathie Wood, told The Guardian that her “sweet and gentle” brother had not opened many letters sent to him and had not known he had to go to the Jobcentre to reapply for benefits.

“He didn't deserve to die. He wasn't harming anyone,” she said.

“He was quite a proud person. He would have wanted to be seen as normal. He was desperate to get by as normal … He didn't want to impose on our mother. He wanted to survive without her help.”

Mr Wood was diagnosed with Asperger syndrome and obsessive compulsive disorder in his late 20s. He later developed an eating disorder and cognitive behavioural problems.

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Ms Wood said she planned to write to David Cameron, who was her brother’s MP, and to Iain Duncan Smith, the Work and Pensions Secretary.

“I would like Iain Duncan Smith to stop talking about this as a moral crusade, and admit that this whole process of reassessing people for their benefits is a cost-cutting measure … This is not just someone being inconvenienced – this is a death,” she said.

A spokesman for the Department of Work and Pensions said: “A decision on whether someone is well enough to work is taken following a thorough assessment and after consideration of all the supporting medical evidence from the claimant's GP or medical specialist. Our sympathy goes out to the family of Mr Wood.”

Tom Pollard, policy and campaigns manager at Mind, said they were “deeply saddened” by Mr Wood’s death.

“Unfortunately this tragic case is not an isolated incident. We hear too often how changes to benefits are negatively impacting vulnerable individuals, who struggle to navigate a complex, and increasingly punitive, system,” he said.

“We know the assessment process for those applying for employment and support allowance is very stressful, and too crude to accurately assess the impact a mental health problem has on someone's ability to work. This leads to people not getting the right support and being put under excessive pressure which can make their health worse and push them further from the workplace.

”We urgently need to see a complete overhaul of the system, to ensure nobody else falls through the cracks.“