SOCIAL class determines how quickly the body ages, irrespective of factors such as health, diet and bad habits, research suggests.

A groundbreaking study of twins led by British scientists has shown that people of lower socioeconomic standing, whether because of the job they do or the person they marry, age seven years more quickly than their more fortunate peers.

Poorer health, worse habits and less pampering may have long been associated with shorter lifespans for Britain’s blue-collar workers, but now biological mechanisms have also be identified.

The study, which involved more than 1,500 women, shows a dramatic and unexplained association between social class and the rate of the body’s cellular deterioration.

Professor Tim Spector, of St Thomas’ Hospital, London, said that the effect could not be explained adequately by low income, poor education or health risk factors known to afflict lower socioeconomic groups most, such as smoking, obesity, lack of exercise and bad diet.

Professor Spector, who works in St Thomas’ twin research and genetic epidemiology unit, said that stress might be the key. People from lower social backgrounds are more likely to feel insecure, especially at work, and suffer low self-esteem and a sense of lacking control over their lives, he said. The stress this causes is thought to inflict damage at a cellular level that accelerates ageing.

The findings, soon to appear in the journal Aging Cell, are the latest to emerge from the twin unit, which is engaged in continuing studies of twins to show how people are affected by genes or the environment.

Professor Spector’s team, working with colleagues in the US, recruited a group of 1,552 British women aged 18 to 75, consisting of identical and non-identical twins. All the women were assigned to one of five officially recognised socioeconomic groups. The scientists then examined their chromosomes, the coiled bundles of DNA in every cell that contain the genes. Chromosomes have protective caps, called telomeres, which act like the ends of shoelaces to prevent them fraying and suffering damage. Telomeres can be likened to time-delay fuses. Whenever a cell divides, they shorten, until a point is reached at which the chromosome can no longer be kept stable.

The cell then stops dividing, its structure and function begin to fail, and it may die.

Experts believe telomere shortening is a marker for biological ageing. Professor Spector found a striking difference in the length of telo- meres between those from working-class and white-collar backgrounds.

Women of the same age were categorised as having manual or non-manual jobs, and the rate at which their telomeres shortened each year was measured. Those from the manual group appeared to have telomere “fuses” that were on average shorter by about seven years.

Biologically speaking, they were seven years “older” than women from the non-manual group, despite having been born at the same time. “We’re talking about a seven-year difference in telomere loss between people of the same age, the same body mass index, and the same smoking and exercise status, who happen to be in a manual or a non- manual job,” Professor Spector said. “A seven-year difference is obviously a large one.”

Risk factors alone could not explain more than a third of the lifespan disparity between social classes, he added.

The scientists went on to compare the telomere lengths of 17 twin pairs who started life in the same social category but then separated, with one moving up the scale and the other down. Generally, this was the result of the women marrying.

In 12 cases relocating to a new socioeconomic group had an even bigger impact on telomere shortening, the equivalent of nine years for women with an average age of 47.

Stress could lead to oxidative damage to cells. The effect would be to speed up the ageing process. “We’re a social species,” said Professor Spector. “I don’t think we’ll ever be in a socialist utopia where everyone is equal and has the same level of stress.”

POWER OF TWO

The twins unit at St Thomas’ Hospital, South London, is the largest performing regular clinical trials, involving 10,000 twin volunteers. To join look at www.twinsuk.ac.uk

Times Recommends

• Everyone will get vaccine against swine flu
• Artificial sperm and the race to build a baby
• BBC jets out stars to tout for prizes