Angela Rippon on her mother's experience of dementia care
Half of all dementia patients leave hospital in a worse state than when they arrive, it is claimed.
The Alzheimer's Society says patients with dementia stay far longer than patients being treated for the same illness or injury without dementia.
It wants their stays cut by a week, saying it will save the health service millions of pounds.
The government said it had already asked NHS hospitals to take urgent action on this issue.
The Alzheimer's Society blames longer stays on a lack of communication, which can exacerbate problems associated with dementia, such as incontinence.
It says there is a need for better clinical leadership, training of nurses to deal with dementia patients and better co-ordination of support services to allow the patient to come out of hospital.
The Alzheimer's Society questioned 1,300 carers who looked after dementia patients and 1,100 nurses in England, Wales and Northern Ireland.
Alzheimer's Scotland said the situation there was not dissimilar.
Ann Reid's mother, Peggy Belcher, was confused and frightened in hospital
Nurses left sign saying: 'You are not well, you need to stay in hospital. Just sit there, rest, relax and don't bang the table'
Ms Reid's mother did not have reading glasses with her nor could she remember anything for more than two seconds
The main reasons for a hospital stay were falls, broken hips or hip replacements, urine infections, chest infections and strokes.
The average length of a hospital stay is about a week but more than half (57%) of dementia patients with a broken or fractured hip stayed two weeks or more.
For urinary tract infections more than half (53%) stayed two weeks or more.
Nearly half of the carers (47%) said being in hospital had a significantly negative effect on the general physical health of the person with dementia.
And more than half (54%) said being in hospital had made the symptoms of dementia worse.
Most of the nurses (89%) said they found working with people with dementia challenging and 80% said they wanted more access to specialist advice.
The society said most of the hundreds of millions of pounds currently spent on dementia in hospitals could be more effectively invested in workforce development and community services outside the hospital.
Neil Hunt, chief executive of the Alzheimer's Society, said: "It is shocking that people with dementia are occupying up to a quarter of hospital beds yet there are scandalous variations in the quality of dementia care in hospitals.
Patients with dementia occupy one in every four hospital beds
"At least £80m a year and probably hundreds of millions could be saved if people with dementia are enabled to leave the hospital one week earlier."
Angela Rippon, ambassador for the society, said she had personal experience of what can happen when a person with dementia has to be admitted to hospital.
"It was awful watching my mother so vulnerable and frightened in this strange, noisy environment full of people she didn't know," she said.
"Some people with dementia are not able to eat or drink due to a lack of appropriate dementia care and many are not being treated with dignity and respect.
"But this important study shows us that staff want to be empowered to deliver good quality care."
The Patients' Association said it was a "sad indictment" of the priority our society gives to elderly people.
"There is now an overwhelming amount of evidence that elderly patients are being neglected in hospitals across the NHS.
"Whether they have dementia or not, if they are in need of help with personal care many of them won't get it. Time after time the issue is raised, but the problems continue."
Care Services Minister Phil Hope said the national dementia strategy published earlier this year had launched a major programme of work to benefit people with dementia across the NHS.
However, he said the report was a reminder of the scale of work that still needs to be done.
"We have set priority areas for all hospitals to take urgent action, including appointing a senior member of staff to improve quality of care for people with dementia, proper training for all staff, and specialist older people's mental health teams working in hospitals.
He said the dementia strategy was backed with "substantial funding" and a national clinical director for dementia was being appointed.
"We expect to see urgent improvements so people with dementia and their carers get the best care the NHS has to offer no matter where they are or what treatment they need," he added.
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