Forgetting where you parked the car, mixing up the names of relatives or leaving your glasses in the fridge are episodes familiar to almost everyone. But at what point do these lapses stop being normal and start to indicate a possible serious cognitive problem?

It is a legitimate question, answered by experts in dementia and ageing for The Guardian, who clarify the thin line between trivial forgetfulness and the early signs of dementia.

Psychologist Kaarin Anstey, director of the Ageing Futures Institute at the University of New South Wales in Australia, says the brain can become “a little slower” through tiredness as well as natural ageing. However, not every instance of forgetfulness is cause for alarm.

What is considered normal?

According to Anstey, forgetting a film title, taking longer to finish tasks or occasionally misplacing objects is acceptable in the ageing process. Neurologist Amy Brodtmann, of Monash University in Melbourne, agrees, stressing that a slowing of mental processing speed is a common consequence of age or tiredness.

Michael Woodward, geriatrician and researcher at the Heidelberg Repatriation Hospital, also in Melbourne, adds that not knowing where you put your keys is not, in itself, a cause for concern. Routine lapses can result from simple distraction and should not immediately be linked to neurological diseases.

"Not all forgetfulness is innocent: when memory fails frequently, the brain may be asking for help."

Mixing up people's names, getting up to do something and forgetting on the way, or occasionally struggling to remember a word are normal failings of brain function, especially at times of stress or fatigue.

When does it become worrying?

The systematic repetition of these lapses, however, does deserve attention. Woodward explains that constantly mixing up names, or frequently forgetting important tasks, may be a warning sign. Even more so if the person begins to leave the cooker on, forget taps running or get lost in places that used to be familiar.

Desmond Graham, medical director of Geriatric Care Australia, warns of changes in speech: stumbling over words, forgetting them or forming incoherent sentences can be early symptoms of dementia.

Amy Brodtmann adds that forgetting emotionally significant events, such as the death of a close friend, or repeating the same story several times in a single conversation, are worrying indicators, often associated with Alzheimer's disease.

Dementia in numbers

According to the National Health Service, dementia is a progressive deterioration of the higher mental functions, including memory, language and mental agility. In advanced stages, it compromises patients' independence and emotional stability.

Alzheimer's disease accounts for 50% to 70% of diagnosed cases. Data from Alzheimer Portugal indicate that, between the ages of 65 and 69, one in 80 women and one in 60 men suffer from the disease. Above the age of 85, one in four individuals is affected.

Prevention and response

Recent studies confirm that hypertension increases the risk of dementia, and that practices such as a balanced diet and regular physical exercise are protective factors.

The experts' recommendation is clear: if there are persistent or progressive signs, the person should consult a general practitioner or a specialist in geriatrics, for proper assessment and follow-up.