Biological age is impacted by smoking and obesity, according to a study published online today in The Lancet.
Obesity and smoking are important risk factors for many age-related diseases, the article notes.
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.
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.
"Our findings suggest that obesity and cigarette smoking accelerate human aging," Professor Spector states.
"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.