Only 41% of people in England and Wales who are living with dementia have had a diagnosis, a figure which is 2% up on last year, according to new research from Alzheimer's Society.
The number of people in England and Wales living with the condition who have been diagnosed has risen 18,000 in a year, from 265,000 to 283,000, says the Society. However, it is estimated that there are now more than 400,000 people with dementia who are not receiving any of the benefits, support and drug treatments that can come from receiving a diagnosis, it adds.
Studies show than an early diagnosis can save the taxpayer thousands of pounds, because it can delay someone needing care outside their own home, it says.
"A diagnosis opens the door to support, benefits and the possibility of medical treatment which can make a real difference to people's lives," said Jeremy Hughes, chief executive of Alzheimer's Society.
"If you find that memory loss is starting to interfere with daily life, then it's important to get it checked out as soon as possible. The sooner people are diagnosed, the sooner they can get the support they need," he advised.
The Society quotes Elizabeth Ashton, whose mother was diagnosed with vascular dementia in 2008 but had shown signs of the disease for at least 10 years before her death last year.
"I thought her forgetfulness was just a sign of ageing and pursuing a diagnosis at the time just didn't occur to me or my GP," said Ms Ashton. "I can see now that we should have been more aware, and an early diagnosis would have been a great help. She might have responded to medication had she been diagnosed earlier, and we would have had a greater understanding of the difficulties she faced," she said.
The Society notes that while there are no drug treatments available that can provide a cure for Alzheimer's disease, medicines are available "that can improve symptoms, or temporarily slow down their progression, in some people."
The two main types of medication used to treat Alzheimer's are cholinesterase inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonists. The cholinesterase inhibitors include Eisai/Pfizer's Aricept (donepezil hydrochloride), Novartis' Exelon (rivastigmine) and Shire's Reminyl (galantamine). The NMDA receptor antagonist, Lundbeck's Ebixa (memantine), is the newest of the Alzheimer's drugs, while Aricept was the first drug to be licensed in the UK specifically for the disease.
The Society has also responded to last week's report from the Harvard Medical School, published on bmj.com, which suggested that nursing home residents over the age of 65 who take certain antipsychotic medications for dementia are at an increased risk of death.
"This research supports existing studies that have shown antipsychotics can raise the risk of death, particularly when used over the longer term. As many as 150,000 of the 180,000 people with dementia who are on the drugs in the UK have been prescribed inappropriately," says the Society.
"For a minority of people with dementia, antipsychotics should be used, but then only for up to 12 weeks, and under the correct circumstances. For the majority, they do far more harm than good," it says, adding: "it is essential alternative treatment approaches are provided to help GPs and other medical professionals reduce the prescribing of these dangerous drugs."
• The World Alzheimer's Report 2010 estimated that an early diagnosis of dementia results in a cost saving for taxpayers of around $10,000 per person with dementia, because it can delay someone needing to be treated in an institution.