People with lower socio-economic status appear to age faster than their better-off counterparts, British researchers said on Thursday.

They showed that the poor have shorter telomeres, the caps on chromosomes that prevent them from fraying, which makes them biologically older than people of the same age in higher social groups.

"Not only does social class affect health and age-related diseases, it seems to have an impact on the aging process itself," said Dr Tim Spector of St Thomas's Hospital in London.

Each time a cell divides, telomeres shorten. The loss is associated with aging which is why telomeres are thought to hold the secrets of youth and the aging process.

The researchers compared telomere length of 1,552 women twins in Britain between the ages of 18 and 75 who were assigned to one of five groups based on National Statistics' Socio-Economic Classification.

Even after adjusting for factors such as obesity, smoking and exercise, which can also influence aging, the scientists found that telomeres in women of lower economic status were significantly shorter.

The average difference was equivalent to about seven years of telomere loss, which also could not be explained by education or income, according to the study published in the journal Aging Cell.

"This is equivalent to what could be considered an extra seven years of biological aging," Spector told a news conference.

"We are talking about a seven-year difference in telomere loss between people of the same age, same body mass index, same smoking status, same exercise status who happen to be in a manual job or non-manual job, which roughly divides the social classes," he added.

When the scientists compared telomere lengths of 17 pairs of twins who had been raised together but as adults were in different socio-economic groups, mainly through marriage, the average difference was equivalent to about nine years' loss.

Spector suspects that lower socio-economic status has an impact on telomere dynamics.

"The idea is that psychological stress itself or the loss of control might have a biological impact," he said. "It might raise levels of oxidative stress in the body and make cells turn over more quickly."

Oxidative stress is damage to cells and DNA caused by free radicals - charged particles found in the environment and produced by processes in the body.