Everyone's Health

DNA shows your real age

Tiny telomeres, the story of aging at the cellular level

S. Lafee

Everyone knows somebody who, truth be told, looks older than his or her age. These folks are wrinklier, fatter, balder, whatever. Chronological time may tick by at a steady rate of one second per second, but people seem to age variably.

Increasingly, there's evidence to back up that observation. Some people actually do age faster. Last year, an English researcher named Tim Spector published a study that suggested obesity accelerates aging – even more than smoking does. This year, he reports that social status appears to affect the rate of aging as well.

In the first study, Spector, a rheumatologist at St. Thomas Hospital in London, measured the length of the ends of chromosomes, called telomeres, in the white blood cells of 1,122 women, ages 18 to 76.

Every time a cell divides, its telomere loses a little bit of DNA and becomes shorter. Eventually, there isn't enough telomere left, the cell stops dividing and dies. It's a kind of chromosomal-age clock.

Spector found that the white blood cells of the youngest women had telomeres roughly 7,500 base pairs in length, and that the average annual telomere loss was 27 base-pairs per year.

But that rate was clearly accelerated when Spector looked at telomere lengths of obese women. Theirs were markedly shorter. He estimated that the difference in telomere lengths between an obese woman and a lean one was 8.8 years of additional cellular aging in the former.

By comparison, studies of smokers' telomeres indicate they are, on average, 4.6 years older than nonsmokers in biological terms. The heavier the smoking habit, the greater the rate of cell aging. Obese smokers were at greatest risk, according to Spector. They average at least 10 years of additional cellular aging compared to lean, nonsmokers.

The damage to telomeres is probably due to free radicals – highly reactive chemicals that oxidize molecules and promote cell mutations. Both smoking and obesity cause oxidative stress, which is a source of free radicals.

The price of being poor. In his newest study, published this month in the journal Aging Cell, Spector reports on a similar study examining the white blood cells of 1,552 female twins.

Based on established annual rates of telomere loss, women in the study with lower socioeconomic standing were more likely to age prematurely and die from cardiovascular diseases and cancer, he says. On average, their telomere lengths were 140 base-pairs shorter than women of the same chronological age but with higher social status. They were, in terms of their cellular age, seven years “older.”

In 17 pairs of twins where the sisters married men at opposite ends of the social scale, the average cellular age difference was even greater – nine years – even though the women were genetically similar.

Spector suggests the link between low status and accelerated cellular aging may be due to psychological stress.

“The greater psychological stress of being in a low social class, with more people above you in the food chain and less control over your life, is the unseen hand that might mean more stress at the cellular level,” Spector told New Scientist magazine. “Oxidative stress does make telomeres shorten.”

To be sure, the connection between telomere length and cell division does not necessarily prove that people who are fat, smokers or menial laborers will die years earlier than others. Humans are complicated organisms, composed of roughly 50 trillion cells. And Spector's work looked at just one kind of cell.

But it's food for thought (albeit not too much). It is well-known that men generally have shorter telomeres than women, a difference of about seven years' worth. That's roughly the same length of time that females live longer on average than males.

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