The key to why a dolphin lives 17 years and a human is 90 years old.

The half-life of a mouse is two years, that of a 90th human, that of a dolphin 17. No one knows very well why. Factors such as body size — larger animals tend to live longer — or heart rate and metabolism have been studied so far. Now, a team of Spanish researchers claims to have found another factor that more accurately predicts how long or short a species's life will be. The key is in the telomeres in the nucleus of each of the cells of a living being.

"We have discovered that only by knowing the speed at which telomeres are shortened can we reliably predict the longevity of a species," explains María Blasco, director of the National Cancer Research Center (CNIO) and lead author of the monday, published in the journal Proceedings of the U.S. National Academy of Sciences.

Telomeres are a protective element of chromosomes, the fundamental structures that store and preserve the genetic information an individual needs to live. Each time one of her cells divides to generate a daughter, telomeres get a little shorter. Exaggerated shortening of these protective tapes is associated with disease and premature aging.

Everything would suit if it wasn't for a fact that until now had no explanation: having very long telomeres is not associated with a longer life. Telomeres in each of a mouse's cells measure five centimeters, while humans are just 4.3 millimeters, Blasco explains. However, humans live 30 times more.

"We are looking at one of the determinants of longevity that is likely to be universal," says María Blasco

Blasco's team has compared the shortening rate of telomeres in nine species of mammals and birds. Researchers have analyzed specimens of various ages of each to calculate not the length of their telomeres, but the rate at which they are shortened over time. The results show that the speed with which this genetic material is consumed predicts the half-life years of each species.

The work details that mice lose 7,000 pairs of bases—telomereric units—a year, while in a human the speed is 100 times less. The work presents a pyramid of life expectancy according to the rate of degradation of telomeres that is crowned by humans, the longest analyzed species and the one that also has the lowest rate of shortening. It is followed by Sumatran elephants (60 years of half-life), flamingos (40), griffon vultures (37), Audouin gulls (21), dolphins (17), goats (16), reindeer (15) and mice (2), the ones who consume their protective genetic material the fastest.

"No study had analyzed the rate of shortening in as many species as we do," says Blasco, whose team has been nourished by animal blood samples from madrid Zoo, as well as blood from seagulls from the Ebro Delta collected by biologists. "We are faced with one of the determinants of the longevity of species that is likely to be universal, since it is preserved from mammals to birds," says Blasco, who also leads the CNIO telomer and telomerase group.

Scientists have been searching for decades for genetic and environmental keys of extraordinary human longevity, such as that of Jean Calment, the human one who has lived for the most years (122), or animals, such as the Icelandic clam (507). Joao Pedro de Magalhaes, a researcher at the University of Liverpool and specialist in studying the genetic factors of longevity, believes that this "is a very interesting study, although what we would all like to see now is whether it is confirmed in a greater number of species." "It will be especially interesting to confirm whether animals that fall out of the norm for having exceptionally long lives despite being small, such as some bats, that reach 40, or the bald mole rat, who lives 32 years, also lose their telomeres to camera slow," he adds.

The researcher points to another important question to be answered. "For now, it has only been shown that there is a correlation between telomeres and longevity, but not causality. This new key may be a cause of premature aging or just a consequence of it, such as gray hair. That's why this work opens up an interesting new field of study," he says.

In 2009, Elizabeth Blackburn, Carol Greider and Jack Szostak won the Nobel Prize in Medicine for discovering telomeres and telomerase, the protein that rebuilds them when they have fallen too short. But lengthening telomeres or curbing their deterioration can have very dangerous side effects, so "for now there is not a single drug based on this molecular mechanism that has proven effective or safe," Blackburn herself last year told IS Country. His advice to reduce the impact of external factors on telomeres is simple: "sleep well, eat well, have a good attitude, don't smoke, don't drink too much, eat a Mediterranean diet and exercise."

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