London, June 13 (Reuters): Obesity and smoking speed up ageing, researchers said today.

They showed that people who smoke cigarettes or are obese have shorter telomeres, the caps on chromosomes that prevent them from fraying, which makes them biologically older than their non-smoking, leaner counterparts.

“Our findings suggest that obesity and cigarette smoking accelerate human ageing,” said Dr Tim Spector, of St Thomas’s Hospital in London.

Telomeres shorten each time a cell divides. The loss is associated with ageing which is why telomeres are thought to hold the secrets of youth and the ageing process. As telomeres get smaller, the chromosomes can become unstable and increase the risk of mutation.

“Obesity and cigarettes cause oxidative stress to increase and this cumulative damage over time causes the loss of these telomeres, which we believe is a marker of accelerative ageing and accounts for why these people get heart disease, diabetes, osteoarthritis and other age-related disease,” Spector said.

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.

Spector and scientists at the University of Medicine and Dentistry in New Jersey compared telomere length from blood samples of 1,122 British women between the ages of 18 and 76. The research is published in the Lancet medical journal.

They found a decrease in telomere length that corresponded to the more obese the women were and the amount of cigarettes they had smoked.