People who smoke or are obese are biologically older than slim individuals and non-smokers, suggests a study published online today by The Lancet.
Obesity and smoking are important risk factors for many age-related diseases. Tim Spector (St. Thomas’ Hospital, UK) and colleagues in the USA looked for evidence of ageing at a molecular level in smokers and obese individuals. They analysed 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.
The investigators recruited 1122 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. 531 women had never smoked, 369 were ex-smokers, and 203 were current smokers. The participants were asked to complete a questionnaire on smoking history. Their exposure to smoking was measured as pack-years (number of cigarette packs smoked per daynumber of years smoking). The investigators measured the concentrations of a body fat regulator called leptin and telomere length in blood samples from the women. They found that telomere length decreased steadily with age and 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 midrange 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.
Professor Spector states: “Our findings suggest that obesity and cigarette smoking accelerate human ageing. . . the difference in telomere length between being lean and being obese corresponds to 8·8 years of ageing; smoking (previous or current) corresponds on average to 4·6 years of ageing; and smoking a pack per day for 40 years corresponds to 7·4 years of ageing. Our results emphasise the potential wide-ranging effects of the two most important preventable exposures in developed countries - cigarettes and obesity.”