Image caption Damage in the brain undetectable by usual scanning has been linked to signs of ageing

Tiny clots in the brain may be the cause of some signs of old age such as stooped posture and restricted movement, say US scientists.

Researchers examining the brains of 418 deceased patients found damaged blood vessels in 29% of them which would not have been picked up by normal scans.

They said higher levels of damage were linked to more limited movement.

The researchers, writing in the journal Stroke, said declining mobility should not be accepted as normal ageing.

Mild symptoms of Parkinson's disease - such as slow movement, rigidity, tremors and posture - increase with age and are thought to affect up to half of people by the age of 85.

Undetectable

A team of scientists at the Rush University Medical Center, in Chicago, carried out autopsies on the brains of nuns and priests who were taking part in the Religious Order Study.

The brains were examined under a microscope for signs of damage which would be invisible to normal brain scans.

If there is an underlying cause, we can intervene and perhaps lessen the impact Professor Aron Buchman, Rush University Medical Center

They found 29% of patients with no previously detected sign of stroke had clotted or narrowed blood vessels.

When comparing the severity of damage with a score of Parkinson's-like symptoms, the study said there was a link.

It concluded that damage, undetectable with current scanning techniques, "may contribute to the development of what is currently considered 'normal' age-related motor symptoms such as parkinsonian signs".

However, it could not prove that the damage itself caused declining mobility, merely that there was a link between the two.

Lead researcher Prof Aron Buchman said: "This is very surprising.

"Often the mild motor symptoms are considered an expected part of aging. We shouldn't accept this as normal aging. We should try to fix it and understand it.

"If there is an underlying cause, we can intervene and perhaps lessen the impact."

Dr Kieran Breen, director of research and development at Parkinson's UK, said: "We know that as people get older they are more likely to develop mini-strokes, so tiny that they cannot be detected by normal scanning techniques.

"Movement problems can occur that are similar to those experienced by people with early mild symptoms of Parkinson's.

"As our brains get older many changes do take place, although there is no evidence from this study that these changes lead to full-blown Parkinson's".