Families with higher levels of a protein linked to inflammation may be at a reduced risk of dementia.
Scientists at the Mount Sinai School of Medicine in New York, USA, tested elderly men without dementia for levels of a substance called C-reactive protein (CRP) and found that those with higher levels were 30 percent less likely to have relatives with dementia.
They also found that the amount of CRP was associated with greater memory quality. 'Those who were doing best in memory function and cognition were the ones with the highest levels of CRP', said study author Dr Jeremy Silverman.
The study involved 277 dementia-free men, aged 75 and over. The researchers interviewed their parents and siblings and found that, of the 1,329 relatives questioned, 40 people from 37 families had dementia. A second, independent group of 51 men was also included, with nine of their 202 relatives found to have the condition.
While CRP has been previously associated with impaired cognition in younger people, the authors suggested that a high amount of the protein in older, dementia-free adults could indicate the presence of other protective factors.
'It's not necessarily that a high level of CRP, which is a bad thing, suddenly becomes a good thing in late age', Dr Silverman explained. 'It's more likely that these people are carrying protection against these bad elements'.
On its website, the Alzheimer's Society pointed out that CRP is actually more likely to be a 'risk factor rather than protection against dementia'. However, it said: 'This interesting research suggests that people who do not develop dementia despite potentially being more at risk might share genetic or lifestyle factors with their families that make them less likely to develop the condition'.
The protective elements are yet to be identified. But it is hoped that by using CRP levels to identify those who are resistant to dementia scientists will then be able to find genes associated with cognition and memory. Dr Silverman hopes that such discoveries will ultimately help develop treatments, or even cures, for dementia and Alzheimer's disease.
'The value of identifying genes is not to pick out the people who are protected, but rather it allows us to understand the mechanisms involved and lead to preventative methods to protect against dementia for those who don't carry the genes', he said.
The study was published in the journal Neurology.