Women might take a tip from their chromosomes. They'll reveal that smoking and obesity can make a 60-year-old body seem like 67.
So concluded researchers here, who measured the relative lengths of telomeres, the protective endcaps of chromosomes, as a marker for biological aging in women who smoked for 40 years. Less smoking also took a chronological toll.
"Our findings suggest that obesity and cigarette smoking accelerate human aging," said co-author Tim Spector, M.D., of St. Thomas Hospital, whose report appeared today online in The Lancet.
Among 1,122 women, current or former smokers had telomere shortening equivalent to 4.6 years of aging compared with never smokers, Dr. Spector and colleagues reported.
Those who smoked a pack a day or more for 40 years had telomeres that were equivalent in length to those of women 7.4 years their (non-smoking) seniors. Each pack-year smoked was equivalent to an 18% increase in telomere loss over baseline.
Obesity appeared to hasten aging the most, with lean women (BMI <20) having significantly longer telomeres than obese women (BMI >30), and medium-sized women having telomere lengths that fell squarely in between.
Telomeres are comprised of amino acid base pairs, but are not genes because they do not encode proteins. They shorten with each cell division and with normal aging, and act as protective mechanisms to prevent broken chromosomes from reuniting with other chromosomal fragments or random bits of DNA, which could lead to growth of severely abnormal cells. When a telomere becomes too short, the cell goes gently into the night, becoming either senescent or dying off.
Because inflammation is associated with increased turnover of white blood cells, "telomere attrition, (expressed in WBCs) can serve as a marker of the cumulative oxidative stress and inflammation and, consequently, slow the pace of biological aging," the investigators wrote.
They recruited 1,122 female twins from a British registry developed to study genetic diseases in women. The women in the sample ranged from 18 to 76 years. In all, 119 had a BMI >30, and 85 had a BMI <20. About half the women (531) had never smoked, 369 had stopped, and 203 were current smokers.
Participants filled out a questionnaire on smoking history, with their smoking exposure recorded as pack-years (number of cigarette packs smoked per day times the number of years of smoking). The authors measured both telomere length and concentrations of leptin, a marker and regulator of body fat.
They found that telomere length decreased steadily and significantly with age, at an average rate of 27 base pairs per year. Obese women had telomeres that were on average 240 base pairs shorter than those of their lean counterparts, a difference that was statistically significant (p = 0.026).
Individuals who had never smoked had longer age adjusted telomeres than former smokers and both had longer telomeres than current smokers (p = 0.02). Among smokers, there was dose-dependent relationship between smoking and telomere atrophy (p = 0.017), and each pack year smoked was associated with a loss of an additional five base pairs (18%).
"Our results emphasize the potential wide-ranging effects of the two most important preventable exposures in developed countries -- cigarettes and obesity," Dr. Spector and colleagues wrote.