New York, April 23 (IANS): People with more demanding jobs may live longer even after developing a form of dementia than people with less skilled jobs, says a new study.

Frontotemporal dementia, which often affects people under the age of 65, results in changes in personality or behaviour and problems with language but does not affect the memory.

"The results show that having a higher occupational level protects the brain from some of the effects of this disease, allowing people to live longer after developing the disease," said Lauren Massimo from University of Pennsylvania in Philadelphia.

People with frontotemporal dementia typically live six to 10 years after the symptoms emerge but little has been known about what factors contribute to this range.

For the study, researchers reviewed the medical charts of 83 people, who had an autopsy after death to confirm the diagnosis of frontotemporal dementia or Alzheimer's disease.

They also had information about the people's primary occupation. Occupations were ranked as factory and service workers in the lowest level; jobs such as trades workers and sales people in the next level; and professional and technical workers such as lawyers and engineers in the highest level.

Researchers measured when the symptoms began by the earliest report from family members of persistently abnormal behaviour.

Survival was defined as from the time symptoms began until death.

The 34 people with frontotemporal dementia had an average survival time of about seven years.

The people with more challenging jobs were more likely to have longer survival times than those with less challenging jobs.

"People in the highest occupation level survived an average of 116 months, while people in the lower occupation group survived an average of 72 months, suggesting that individuals, who had been in the professional workforce may live up to three years longer," the authors noted.

The study found that occupational level was not associated with longer survival for the people with Alzheimer's disease.

The findings add evidence to the "cognitive reserve" theory that experiences such as more education, higher occupation and mental activity build up connections in the brain that create a buffer against disease.

The paper appeared online in the journal Neurology.