People do not always recognise the signs of dementia
People suffering from memory loss need to act more quickly in seeking medical advice, experts warn.
The Alzheimer's Society said up to two-thirds of people in England with dementia are never diagnosed as they do not recognise the symptoms.
The charity is giving GPs in England posters and leaflets to raise awareness about the issue and a toolkit to support diagnosis.
It is estimated by 2025 over 1m people in the country will have dementia.
The Department of Health is backing the Alzheimer's Society campaign to raise public awareness of symptoms and the importance of an early diagnosis.
Health Minister Ivan Lewis said: "Dementia is now one of the most significant health challenges facing our society.
"That is why we are determined to bring dementia out of the shadows."
Currently 700,000 people in the UK live with the disease and one-in-three people over the age of 65 will die with it.
WHEN TO SEEK HELP
Do you struggle to remember recent events while finding it easy to recall things that happened in the past?
Do you find it hard to follow conversations or programmes on TV?
Do you regularly forget the names of friends or everyday objects?
Do you find it difficult to recall things heard, seen or read?
Do you struggle to make decisions?
Do you repeat yourself in conversation or lose the thread of what you are saying?
Do you have problems thinking and reasoning?
Do you feel anxious and depressed or angry about forgetfulness?
Do other people comment on your forgetfulness?
There are more than 100 different types. Alzheimer's disease is the most common type, affecting 62% of those diagnosed. Others include vascular dementia and mixed dementia.
For those who do report their symptoms to the GP, it takes an average of nearly three years for a diagnosis from first noticing symptoms, the Alzheimer's Society said.
Neil Hunt, its chief executive, said: "There is an acute lack of awareness and understanding of dementia.
"By encouraging people who are worried about their memory problems to seek medical advice sooner than they might have done, we hope more people with dementia can get care early on, giving them a greater chance to live life as well and as fully as possible."
He added that people could reduce their risk of dementia by cutting down on salt, eating lots of fruit and vegetables, keeping active and watching their weight.
A recent study by the National Audit Office found only 30% of GPs feel that they have enough basic information and training to diagnose and manage the disease.
Professor Steve Field, chair of the Royal College of GPs, said it could be hard to diagnose dementia but patients would be encouraged to visit their GP if they had concerns.
"There are treatable causes of memory loss and GPs are always happy to see patients who are concerned and we can reassure them and if not we can offer treatment and support."