The University College London study involved patients with frontotemporal dementia, with the results appearing in the Journal of Alzheimer’s Disease.
Questionnaires from the friends and family of the 48 patients revealed many had noticed a change in humour years before the dementia had been diagnosed.
This included laughing inappropriately at tragic events.
Experts say more studies are now needed to understand how and when changes in humour could act as a red flag for dementia.
There are many different types of dementia and frontotemporal dementia is one of the rarer ones.
The area of the brain it affects is involved with personality and behaviour, and people who develop this form of dementia can lose their inhibition, become more impulsive and struggle with social situations.