Patients are living with dementia for less time, study finds

Dementia patients are being diagnosed later in life – and therefore living less time with the disease, a new study has found.

The average age at which patients are being diagnosed has increased by six years in three decades.

Breakthroughs in the prevention and care of stroke, which can trigger the disease, may partly explain the trend: the number of stroke victims developing dementia has more than halved in 30 years. 

But other factors including vaccination programs, a reduction in lead pollution and better education and nutrition could also be behind the phenomenon.

Professor Sudha Seshadri and her colleagues said it is good news dementia’s impact ‘might be compressing a bit.’

That is, people might be developing it later and living with it for a shorter period of time.

The researchers said a diagnosis such as ‘Your father has Alzheimer’s disease’, or ‘Your mother has stroke-related dementia’ is one a family never wants to hear.

But general improvements in health have at least helped to ward off severe mental decline.

Senior author Professor Seshadri, founding director of the Glenn Biggs Institute for Alzheimer’s & Neurodegenerative Diseases at the University of Texas, San Antonio, drew on the Framingham Heart Study which has been following residents of the Massachusetts town for decades.

Using data on 5,205 participants during four different periods from 1977 to 2008 her team found the average age at dementia onset increased – while the length of time living with it decreased.

At the start of the study those diagnosed with dementia were 80 years old on average – and 86 when they died.

By the end they were 86 when they were diagnosed – and nearly 90 when they died.

Prof Seshadri said: ‘On average, the age at onset of dementia has increased by two years every decade whereas the survival after dementia diagnosis has fallen from six years on average in 1977–1984 to three years on average in 2004–2008.’

She added: ‘Prevention of stroke and reduced impact of stroke are great advances, but neither completely explains the trend we are seeing.

‘We are looking at other causes, such as lower burden of multiple infections because of vaccination, and possibly lower levels of lead or other pollutants in the atmosphere. Early education and nutrition might also play a role.’

Overall, among all the participants five-year mortality risk was 33 percent lower in the last epoch compared to the earliest.

The study, published in the Journal of Gerontology, said stroke risk has reduced because of greater control of blood pressure.

Citing the Framingham data, Prof Seshadri said: ‘In the past, if you had a stroke you were at 90 percent greater risk to develop dementia. Today, you have a 40 percent greater risk.’

She said several epidemiological studies have suggested dementia prevalence reducing with age over the last three decades. But it was unclear if this delayed clinical onset was accompanied by a shorter survival time after diagnosis.

So her researchers carried out a study of 317 dementia cases and the same number of controls matched on age, gender and time period.

In those who developed dementia, age at onset increased by about 18 months per epoch – and years alive with it decreased by a year per epoch – over time.

Mortality risk also fell by 18 percent in dementia patients in 1986 to 1991 compared to 1977 to 1983. But there was no significant change from then to the last epoch.

Prof Seshadri added: ‘There are so far only putative explanations of declining dementia trends.

‘They could be the consequences of this last century improvements in education achievement, medical care, lifestyle changes and primary and secondary preven- tion of cardiovascular and cerebrovascular conditions that would have been beneficial for preserving cognitive health longer.’