Everybody ages, but the pace may pick up with obesity and smoking.

A new study isn’t intended to be alarming. It has limitations, having only looked at genetic markers in white blood cells of about 1,100 healthy white women.

Still, the researchers don’t pull any punches. “Our findings suggest that obesity and cigarette smoking accelerate human aging,” write professor Tim Spector, MD, and colleagues. Spector directs the Twin Research and Genetic Epidemiology Unit at St. Thomas’ Hospital in London. The study appears in The Lancet’s online edition.

Obesity and smoking have both repeatedly been shown to be serious health hazards. However, they can also be overcome. If Spector’s study is right, the finding may be one more reason to go for a smoke-free life at a healthy weight, even if it takes hard work and time to get there.

Read WebMD's "10 Little-Known Reasons to Quit Smoking"

Cellular Aging Study

The women in Spector’s study were all twins aged 18-76 years. The group consisted of 45 pairs of identical twins and 516 pairs of nonidentical twins.

The researchers examined the length of the telomeres in their white blood cells. Telomeres are the tips of the chromosomes, which contain DNA. They gradually shorten over a lifetime. That’s a normal part of the aging process. Telomere length was checked by isolating white blood cells from the women’s blood samples.

Read WebMD's "Quit Smoking: Your Guide to Kicking the Habit"

Estimated Effects

Smoking and obesity were linked to shorter telomere length, say the researchers.

Assuming their results pan out, the researchers were able to estimate the number of years lost to cigarettes — or extra pounds.

— The difference in telomere length between being lean and being obese corresponds to 8.8 years of aging.

— Smoking (previous or current) corresponds on average to 4.6 years of aging.

— Smoking a pack per day for 40 years corresponds to 7.4 years of aging.

Keep in mind that those time spans refer to telomere length, not overall aging.

“Our results emphasize the potential wide-ranging effects of the two most important preventable exposures in developed countries — cigarettes and obesity,” write the researchers.

They point out that there was “considerable variation” in telomere length between participants and call for larger studies on the topic.

Read WebMD's "Are You Overweight? Calculate Your BMI"

Possible Explanation

“Obesity and smoking are important risk factors for many age-related diseases. Both are states of heightened oxidative stress … and inflammation,” say the researchers. That could wear down the white blood cells’ telomeres, and bigger studies should be done to check that, the study notes.

Other researchers have also suggested that telomere length indicates aging. In May, a small study tied weight gain and insulin resistance to shortened telomeres. That report appeared in the journal Circulation.

Last November, a study in the Proceedings of the National Academy of Sciences showed a link between chronic stress and shorter telomeres. A third study, published in The Lancet’s Feb. 1, 2003 issue, showed an association between shorter telomeres and greater risk of deathfrom heart disease and infectious diseases.

By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: Valdes, A. The Lancet, June 14, 2005; online edition. WebMD Medical News: “Extra Weight May Age You Faster.” WebMD Medical News: “Chronic Stress May Make Cells Age Faster.” WebMD Medical News: “Life Span Lives in Length of Chromosomes.” News release, The Lancet.