People with Alzheimer's and similar conditions are being promised more government help.
Health Secretary Alan Johnson will on Tuesday unveil a national dementia strategy which he claims will transform the treatment of 700,000 sufferers.
Mr Johnson told BBC One's Andrew Marr show dementia should be discussed more openly to end the "stigma" and "cruel humour" surrounding it.
The aim was to get people to seek diagnosis earlier, he said.
At the moment, it took three years, on average, for someone suffering from to seek diagnosis, Mr Johnson told BBC One's Andrew Marr show.
He said: "It's a bit like cancer was 20 years ago. It wasn't the subject of polite conversation. But unlike cancer, there is some pretty cruel humour attached to dementia and Alzheimer's, which is a form of dementia."
He said the government's strategy was aimed at raising the profile of dementia, increasing early diagnosis and improving the quality of treatment.
He said there were memory-enhancing drugs and changes to diet and lifestyle which could help the onset of dementia if the condition is diagnosed early enough.
He pledged more specialised "memory clinics" and better support for carers.
He also conceded that the NHS had to be "rebalanced" to prevent discrimination against older people but he said he hoped the days "a clinician would say 'Well, it's not worth operating or let's not give medication to that person because they are too old'" were over.
He insisted money would be available to pay for the dementia strategy, but said full details would be announced in the House of Commons on Tuesday.
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