'Our results emphasize the potential wide-ranging effects of the two most important preventable exposures in developed countries -- cigarettes and obesity.'

Tim Spector of St. Thomas' Hospital, UK, and colleagues in the US looked for evidence of aging at a molecular level in smokers and obese individuals.

They analyzed telomeres, which cap the ends of the chromosomes in our cells and protect them from damage. Every time a cell divides, and as people age, their telomeres get shorter.

How Long Are Your Telomeres?

The investigators recruited 1,122 women from the UK aged 18-76 years onto the study. 119 of the women were obese, with a body mass index (BMI) greater than 30, and 85 women had a BMI under 20.

The participants were asked to complete a questionnaire on smoking history; 531 women had never smoked, 369 were ex-smokers, and 203 were current smokers. Their exposure to smoking was measured as pack-years (number of cigarette packs smoked per day multiplied by the number of years smoking).

In addition to telomere length, the investigators measured the concentrations of a body-fat regulator called leptin in blood samples from the women. They found that telomere length decreased steadily with age and that the telomeres of obese women and smokers were much shorter that those of lean women and never-smokers.

Lean individuals had significantly longer telomeres than women with mid-range BMIs, who, in turn, had longer telomeres than obese individuals. Each pack-year smoked was equivalent to a loss of an additional 18% on top of the average annual shortening of telomeres.

Preventable Risk Factors

"Our findings suggest that obesity and cigarette smoking accelerate human aging," Professor Spector states.

"The difference in telomere length between being lean and being obese corresponds to 8.8 years of aging," he points out.

"Smoking (previous or current) corresponds on average to 4.6 years of aging; and smoking a pack per day for 40 years corresponds to 7.4 years of aging," he adds.

"Our results emphasize the potential wide-ranging effects of the two most important preventable exposures in developed countries -- cigarettes and obesity," Professor Spector concludes.