According to the Centers for Disease Control and Prevention, 64 percent of American adults aged 20 years are either obese (have a body mass index, or BMI, of 30 or above) or overweight (BMI 25 or above).
Dr Tim Spector of St Thomas' Hospital in the UK set out to test the hypothesis that increased body mass and smoking - both of which are known to heighten oxidative stress - are connected to shortened telomere length in white blood cells.
Telomeres are sequences of DNA that cap the ends of chromosomes in cells and protect them from damage. The shortening of telomeres is a process that occurs naturally with aging, every time a cell divides. But oxidative stress is known to increase the erosion of telomeres with each replication.
For the study, published today in the online version of The Lancet, Dr Spector's team recruited 1122 white women aged between 18 and 76 years. Of these, 119 had a BMI of over 30 and 85 had a BMI of under 20. In a questionnaire about their smoking habits, 203 said they were current smokers, 369 were ex-smokers and 531 had never smoked.
The mean rate of telomere length decrease across all the participants was 27 bp per year. But the telomeres of the obese women were seen to be 240 bp shorter than those of lean women, making them more than nine years 'older' in biological terms.
Using a dose dependent measure dubbed the 'pack year' - that is, cigarette packs smoked per day multiplied by the number of years smoking - the researchers noted that each pack-year was associated with 5 bp more telomere length lost.
"Our results emphasize the pro-aging effects of obesity and cigarette smoking," concluded the researchers.