Dementia symptoms are emerging 6 years later than in previous generations

Modern day patients with dementia are living for a shorter period with the disease, a new study has found. Scientists at the Glenn Biggs Institute for Alzheimer's & Neurodegenerative Diseases at the University of Texas, San Antonio have discovered that people are being diagnosed later in life than previous generations.

Over the past 30 years, the average age to be diagnosed with dementia has increased by six years. It is thought that this is partly due to breakthroughs in the prevention of and care for those who have had strokes, as they can trigger dementia.

In fact, the number of stroke patients who go on to develop dementia has been reduced by more than half in the last three decades. Researchers believe there are other contributing factors too, however, including vaccination programmes, a drop in lead pollution and better education on nutrition.

Senior author Professor Seshadri, founding director of the institute, 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.

“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,” she added.

The team analysed data from 5,205 patients across four separate time periods ranging from 1977 to 2008. At the beginning of the study, the average age of diagnosis was 80, with death coming at 86. By the end, this had raised to 86 for diagnoses and 90 was the average age at which they died.

Speaking about the data, Professor Seshadri said that in the past, people had a 90 per cent stronger risk of developing dementia if they had experienced a stroke. Now, the chances have been slashed to 90 per cent, with hopes there could be even further improvement in the future.

A number of epidemiological studies had suggested that dementia prevalence has been going down in the last 30 years, but there was much uncertainty around it. Among the lack of understanding was as to whether survival time after diagnosis was also seeing a reduction.

In a bid for more clarification on the issue, the team looked in more detail at 317 dementia cases. They were matched with controls that had the same age and gender and had been monitored during equivalent time periods.

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 prevention of cardiovascular and cerebrovascular conditions that would have been beneficial for preserving cognitive health longer.”