Lack of respect for the elderly in western societies could be fuelling the Alzheimer’s epidemic and simply allowing people to grow old gracefully could prevent dementia, scientists have suggested.

The study by Yale School of Public Health, in the US, is the first to show that social and cultural stereotypes can influence the development of age related disease.

Put simply, people who have been conditioned by society to think they will become physically and mentally decrepit in older age, probably will. The stress of such negative thoughts may actually alter the brain and trigger dementia, scientists believe.

In contrast, upbeat, optimistic and active individuals who refuse to conform to ageist stereotypes, are likely to stay mentally alert for longer.

The researchers say it could explain why westernised countries like the UK have such a high rate of dementia compared with India, where the elderly are venerated.

"We believe it is the stress generated by the negative beliefs about aging that individuals sometimes internalise from society that can result in pathological brain changes," said lead author Dr Becca Levy.

"Although the findings are concerning, it is encouraging to realize that these negative beliefs about aging can be mitigated and positive beliefs about aging can be reinforced, so that the adverse impact is not inevitable.”

To test the link between negative stereotypes and dementia, researchers looked at 158 people who had their brain scans once a year, for 10 years, as part of the Baltimore Longitudinal Study on Aging. Their average age was 68.

All were quizzed about their attitudes to ageing and asked to say how much they agreed with statements such as ‘old people are absent-minded.’ Scientists also studied the area of the hippocampus in the brain, which is known to shrink in people with Alzheimer’s.

As predicted, participants holding more-negative age stereotypes started with far lower hippocampal volume which declined steeply over the 10 year study period.

The team also looked at the brain of 78 people who had died during the research to examine two other indicators of Alzheimer's disease: amyloid plaques, which are protein clusters that build up between brain cells; and neurofibrillary tangles, which are twisted strands of protein that build up within brain cells. Participants holding more negative beliefs about aging had a significantly greater number of plaques and tangles.

Researchers at Yale believe that the problem is being made worse by ubiquitous negative stereotyping of the elderly in society. The same team carried out a study of Facebook in 2013, and discovered that 98 per cent of references to older people on the social networking site were negative.

The research was published in the journal Psychology and Ageing.