Experiencing “senior moments” may be a good sign rather than a cause for concern, research suggests. The time to worry is when you begin to stop noticing memory lapses, scientists have shown.

A study, published in the journal Neurology, found that people with dementia tended to lose awareness of memory problems two to three years before the condition developed.

US lead researcher Dr Robert Wilson, from Rush University Medical Centre in Chicago, said: “Our findings suggest that unawareness of one’s memory problems is an inevitable feature of late-life dementia, driven by a build-up of dementia-related changes in the brain. Lack of awareness of memory loss is common in dementia, but we haven’t known much about how common it is, when it develops or why some people seem more affected than others.

“Most studies of memory unawareness in dementia have focused on people who have already been diagnosed. In contrast, this new study began following older adults before they showed signs of dementia.”

The team tracked the progress of more than 2,000 older individuals with an average age of 76 who were free of dementia at the start of the study. Over a period of 10 years, they were given annual tests of memory and thinking ability. Participants were asked how often they had trouble remembering thingsand how they rated their memory.

For the 239 volunteers diagnosed with dementia, memory awareness began to drop sharply an average of 2.6 years before they developed symptoms. Several years of memory decline followed.

“Although there were individual differences in when the unawareness started and how fast it progressed, virtually everyone had a lack of awareness of their memory problems at some point in the disease,” said Wilson.

Loss of memory awareness appeared earlier in younger participants. The explanation may be that older people were more likely to expect their memories to fade as a normal part of ageing, said the scientists.

An examination of the brains of 385 individuals who died during the study revealed three dementia-related changes associated with rapid decline of memory awareness.

Wilson said: “This study underscores the importance of family members looking for help from doctors and doctors getting information from friends or family when making decisions about whether a person has dementia, since people may be unable to give reliable reports about the history of their own memory and thinking abilities.”