Two major health hazards - smoking and obesity - can add yet another feature to their dossier of potential health risks. A study published in The Lancet has linked both to hurrying up the aging process.

Dr. Tim Spector of St. Thomas Hospital in London led a team of researchers who concluded, "our findings suggest that obesity and cigarette smoking accelerate human aging."

The study examined about 1,100 Caucasian women in Britain, focusing on the telomere length of their white blood cells. Telomeres are end caps of chromosomes, which contain DNA. Telomeres are believed to shorten over a person's lifetime as a function of the aging process.

The researchers found that obese women, as well as those who smoked over a prolonged period, had shorter telomeres compared to lean women and those who smoked less or not at all. Specifically, the researchers determined that smoking contributed to about 4.6 years of aging, while obesity can age a person by nearly nine years.

It is important to keep in mind that the years of aging determined here relate to the length of telomeres, and not of overall aging.

"Obesity and smoking are important risk factors for many age-related diseases," the researchers said. "Both are states of heightened oxidative stress…and inflammation," which may be associated with the accelerated aging of white blood cells.

All participants in the study were twins and were between the ages of 18 and 76. Roughly half of these women had never smoked while 369 had smoked previously but stopped, and 203 currently smoke.

Those who smoked at least a pack a day for more than 40 years had telomeres that were as long as non-smoking women who were over seven years older. Each year of smoking was responsible for contributing to an 18 % increase in telomere loss.

Other studies have supported Spector's hypothesis regarding the connection between the length of telomeres and aging. For instance, one study drew an association between shorter telomeres and a greater risk of death from heart disease and infectious diseases, while another indicated a link between shorter telomeres and chronic stress.

Overall, the study lends support to the belief that being lean and smoke-free can prevent your life from being cut short. "Our results emphasize the potential wide-ranging effects of the two most important preventable exposures in developed countries-cigarettes and obesity," wrote the researchers.

The study was based on a limited sample of subjects and the researchers agreed on the need for further research on the topic.