As Alzheimer's Australia president, Buttrose is leading a Fight Dementia march on Thursday, which will call for an extra $500million over five years for dementia in the 2012-13 budget.

The money would be used to reduce the stigma of the disease, promote faster diagnosis, increase research and invest in dementia prevention and care.

''It's such a major health issue,'' Buttrose said of the ultimately fatal disease that can involve a loss of memory, intellect, rationality and social skills.

The cause is so important to the former Cleo editor that she announced yesterday she would not run for Lord Mayor of Sydney, despite strong polls in her favour and mounting speculation.

''I decided not to run for the position of Lord Mayor as my commitment to Alzheimer's Australia and the fight against dementia is more important to me than running for Lord Mayor,'' she said.

Buttrose said she wants to see the Government make dementia a health priority.

''Everybody fears losing their minds ... we really need to take it seriously,'' she said.

''There is this assumption that older people don't matter, that they're going to die.''

According to a recent Access Economics report, about 269,000 Australians live with dementia and each week, 1500 Australians are diagnosed with the disease.

With Australia's rapidly ageing population, the number of dementia sufferers is set to rise to about 981,000 by 2050.

Buttrose has had personal experience with the disease, having cared for her father who suffered vascular dementia.

''Almost everybody knows somebody who's been affected ... I can tell you what, it's a pretty terrible diagnosis.''

Buttrose, who has enjoyed a recent return to the limelight courtesy of the ABC's Paper Giants: the Birth of Cleo mini-series, wants to counter the perception that dementia is just a normal part of ageing. ''There's still a lot of ignorance,'' she said.

''You've really got to look after your brain the whole of your life.''

Minister for Mental Health and Ageing Mark Butler will speak at the rally on Thursday and meet Alzheimer's Australia.

But a spokeswoman for Mr Butler said that funding had not been cut from dementia initiatives - as asserted by the Fight Dementia campaign.

The spokeswoman said the Government provided $8.3 billion for people in aged care homes.