There's no right answer when someone asks you: "How old do you think I am?"

Faced with such a dilemma, most of us aim low—erring on the side of flattery rather than honesty. But the truth is, accurately guessing someone's age is a difficult task, perhaps best left to amusement park workers and street performers.

Why is it that some people just look older (or younger) than they really are? Scientists may have found the answer.

Chronological age is very different from biological age—the condition of chromosomes after each cellular division—according to Nilesh Samani of the University of Leicester, co-author of a February 7 report published in Nature Genetics. Biological age, Samani says, is related to the length of telomeres—stretches of DNA at the ends of chromosomes, which protect these precious packages of genes from daily wear and tear. We're born with telomeres of a certain length, and these get shorter as our cells divide, resulting in aging, scientists think.

But not all telomeres are born equal. Telomere length varies from person to person, but is similar in siblings, suggesting it might be under some genetic control. Samani and his colleagues analyzed more than 500,000 genetic variations (naturally occurring, single-nucleotide differences) spanning the genome in blood cells collected from almost 3,000 people. The researchers found that individuals carrying a particular genetic variant had shorter telomeres—meaning less padding for those fragile genes. The variant lies near a gene called telomerase RNA component, or TERC, and earlier studies in animals have shown that low TERC expression is associated with shorter telomeres, and faster biological aging.

The telomeres of people carrying one copy of the variant looked on average three to four years older, according to their lengths, than those of someone the same chronological age without the variant. There also was a gene dosage effect: Two copies of the variant (one inherited from each parent) resulted in an additive aging effect of six to eight years—meaning that a 50-year-old carrying two copies of the variant had the telomeres of someone aged 58. The results suggest that some people are genetically programmed to age at a faster rate, according to study co-leader Tim Spector, from King's College London.

The odds of carrying the variant are relatively high, Samani says. "In the populations we studied, about 7 percent of people carried two copies of the variant and about 38 percent of people [carried] one copy." But it's unknown whether shorter telomeres make their carriers physically appear older than they really are. "We haven't looked at that—it's an interesting question," he says; pondering how to measure the age someone looks in a follow-up study. Maybe we'll take pictures of the participants and a have a panel guess their age," he adds jokingly.

Samani, a cardiologist and professor of cardiology, is more interested in whether people carrying the variant are at a higher risk for developing age-associated illnesses like heart disease. "I see people in their eighties who have very normal arteries, and people in their forties with cardiovascular disease," he says. Previous work published by Samani has linked telomere shortening with heart disease, suggesting that biological age may be more relevant to age-related diseases than chronological age. "We've got a marker for biological aging—telomere length—so we're studying whether we can relate it to the increased risk of getting some of these age-associated diseases. That would certainly put the concept of biological aging on firm foot[ing]."

9 Comments

1. 1. j3gibson 03:42 PM 2/8/10

   this is very interesting. I wonder if the gene is more affected by sunlight exposure or free radiacals since the appearance of someone's skin is the biggest indicator of age.

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2. 2. jonitiranes 05:54 PM 2/8/10

   Unless it is UV rays, I am inclined to think that sunlight has no significant effect on telomeres. Skin conditioned by sunlight is a phenotypical change.

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3. 3. Crucialitis 08:17 AM 2/9/10

   What if telomeres have encoding that tells polymerase how many mistakes it can make?

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4. 4. talslsels 10:47 AM 2/9/10

   I'm not sure if it's me who can't understand it.
   "Individuals carrying the variant had shorter telomeres, stretches of DNA at the ends of chromosomes that protect them from daily wearand also aging"
   From here, it says shorter telomeres tend to protect people from getting old.
   While in that content, it says people have one copy of that genetic variant that is believed to have relation to a shorter telomere would make people look on average 3 to 4 years older.
   Can you really afford a mistake that clear in the title??

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5. 5. sparcboy 12:34 PM 2/9/10

   OK, so what can a person do or not do in order to stabilize the telomeres and prevent them from breaking down, i.e. what should we do or not do in relation to telomeres to prolong health and life?

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6. 6. William O'Connor 03:17 PM 2/9/10

   What causes telomeres to shorten and to break off?

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7. 7. kmoisse in reply to talslsels 06:15 PM 2/9/10

   The telomeres are stretches of DNA that protect the chromosomes. As they get shorter, they offer less protection to our genetic material. This, the researchers say, is what underlies biological aging.

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8. 8. fisixisfun 04:24 AM 2/10/10

   If I remember my high school IB Biology correctly, the reason telomeres affect aging is that DNA can only be copied in the 5'-->3' direction (or the reverse, my mind has been known to flip things), and when copying in the opposite direction it has to put down a lot of initiator enzymes, with nucleotides then being added behind them. Imagine a zipper unzipping. On one side, the links are in the right order, so only one initiator is needed, then the nucleotides just add on, following the zipper. But on the other side they are going the wrong way, so initiators must be placed right behind the zipper and then fill in backwards, and once more space opens up, another initiator gets put down. When the initiators are removed, the DNA that they covered isn't replaced, so that part is lost, and the telomeres basically act as disposable DNA that gets covered instead of the important stuff. Once the telomeres are gone, important DNA starts being covered, and things start to break down. I could be wrong about this though, DNA replication is not my strong suit.

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9. 9. pf1624@yahoo.com.hk 05:38 AM 2/10/10

   There is still some genes in which their functions are not understood yet. Maybe the genetic variant linked could contribute to the shortening of telomeres as well as inheritable diseases associated on cardiology.

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