New figures due to be published this week reveal that 42,000 people are now living with early onset dementia in the UK.
Previously it was believed that just 17,000 cases of dementia were in younger people.
But the new figures show that cases in people under the age of 65 represent 5% of all dementia cases.
Thousands of people have the condition in their 40s, and more than 700 people have been diagnosed in their 30s.
The Alzheimer’s Society, the London School of Economics and King’s College Institute of Psychiatry are due to release the figures on Wednesday.
Jeremy Hughes, chief executive of the Alzheimer’s Society told The Telegraph:“Many people will be coming to terms with the symptoms while still in work, perhaps looking after children and paying a mortgage. Too often we hear of people reporting memory loss to their doctor in mid-life, but being misdiagnosed because they are considered too young to have dementia.”
Hughes said that services must ensure younger adults are also able to access specialist treatment and support.
The report suggests that the number of people with early-onset dementia will rise by 20% over the next forty years, with more than 50,000 cases expected by 2051.