Smoking and obesity linked to ageing genetic material

Obesity and smoking can result in changes to genetic material indicative of cellular aging, according to a new UK study. The research, carried out at St Thomas' Hospital in London, shows that women who are obese, or who are heavy smokers have shorter telomeres - protective caps on the ends of a cell's chromosome. The team, who published their findings in the Lancet, say the ageing effect may explain why such women are at increased risk of age-related health problems.      

The researchers collected health information and blood samples from 1,122 women aged between 18 and 76 years. Around 11 per cent were clinically obese, and about 18 per cent were active smokers. They looked at the ends of the chromosomes (bundles of genetic material found in almost every body cell) present in white blood cells. In particular, they measured the length of the telomeres of the chromosomes.

It has long been known that telomeres act as a kind of cellular clock, marking the number of times a cell has replicated its genetic material. Each time a cell divides to make two new cells, its telomeres get shorter, until eventually it stops multiplying altogether. So the length of a cell's telomeres, measured in base-pairs (chemical 'letters') of DNA, reflects the age of the parent cell. A study published in 2003 suggested that people with shorter telomeres may die earlier than those with longer telomeres.

In the latest study, the researchers found that the telomeres of obese women in the study were nine years 'older' than slim women of the same age, while those of heavy smokers were seven years older. Overall, the telomeres of the women in the study shrank by about 27 DNA base-pairs per year, but the telomeres of those who had smoked for over forty years were around 200 base-pairs shorter than non-smokers. Being overweight had an even greater effect - the telomeres of obese women were, on average, 240 base-pairs shorter than those of slim women.

The authors stress that they have only looked at white blood cells so far, and obesity and smoking may not have the same effect on other body tissues. They now plan to look at the effect of other lifestyle factors on telomere length, such as exercise, diet and occupation.