London: Young women who smoke and who are overweight will age faster than their slimmer friends, according to a new medical study by doctors at St Thomas’s Hospital in London.

Being obese will add an average of nine years to a woman’s biological age, while smoming will add another five years. The study concluded that these factors damage the genetic make-up of normally healthy cells.

The study – led byProfessor Tim Spector, of St Thomas’s Hospital in London – is published in the medical magazine, The Lancet.

Professor Spector said that the evidence from his study suggested that the whole body was being damaged.

He said: ‘These lifestyle factors mean you may die earlier. You’ll also be looking and feeling older before your time.’ The study looked at the length of telomeres – tiny ‘caps’ on the ends of chromosomes which help protect DNA from ageing processes.

Telomeres have been called the ‘chromosomal clock’ because they appear to be central to biological ageing. They shorten over time and after a certain point can no longer prevent the DNA from falling apart.

The team, which included U.S. researchers experts in telomeres, looked at 1,122 white women aged 18 to 76. Half were from pairs of identical and half from non-identical twins. Comparing identical and nonidentical twins can reveal which traits are purely inherited.

The telomeres in the women’s white blood cells were measured. On average, telomeres shortened by two base pairs – components of DNA – a year. However, there were enormous differences depending on smoking habits and body fat. On average, women who smoked at any time in their lives had an extra 4.6 years reduction in telomere length. Those who smoked 20 cigarettes a day for 40 years, or 40 a day for 20 years, added 7.4 years to their biological age. Being obese corresponded to 8.8 extra years, while the two factors together added at least 10 years.

Professor Spector said overweight women appeared to accumulate this level of cell damage at a relatively young age, probably by the time they are in their 30s.

Although the study only included women, he believes the findings would also apply to men.

It is thought smoking and excess body fat unleash free radicals and trigger inflammation, which boosts the turnover of white blood cells and speeds up the erosion of telomeres.