The biological age and life expectancy of an individual can be predicted by measuring the telomere length of DNA. This was discovered by researchers from the University of Groningen and two British universities during research on the length of chromosome caps – known as telomeres – in a wild population of Seychelles warblers on a small isolated island. The research will be published today in the journal Molecular Ecology.
Telomeres get shorter as you get older, but the research reveals that the speed at which this occurs differs among individuals. It also turns out that having shorter telomeres is related to an increased chance of mortality. Telomere length predicts future life expectancy better than actual age and could thus serve as a measure of biological age.
Telomeres are located at the ends of the chromosomes. Just like the hard plastic ends of shoelaces, they function as protective caps that prevent the genes close to the end of the chromosome degenerating. Over time the telomeres break down and become shorter. When they reach a certain critical length, the cells they are in stop functioning.
‘This mechanism has evolved to prevent cells replicating out of control – becoming cancerous’, says research leader Dr David S. Richardson of the University of East Anglia. ‘The flip side is that health issues then arise. Telomeres protect against cancer, but also ensure that we age.’
The research project lasted a total of twenty years. It is the first study that measures telomeres over the entire lives of individuals in a wild population. The researchers studied the population of Seychelles warblers on Cousin Island in the Indian Ocean. Twice a year they collected blood samples from these birds and analysed the length of the telomeres.
‘We wanted to investigate what happens over an entire lifetime. To that end, Seychelles warblers are ideal research subjects’, says Martijn Hammers of the University of Groningen. The birds have no predators on this remote island and are confined by natural boundaries. ‘As a result we could follow individuals throughout their lives until they died of old age.’
The researchers investigated whether telomere length at any particular age could predict whether a bird would soon die. With short telomeres and telomeres that shortened quickly, it turned out that the chances of the bird dying within a year were high. The researchers also saw that individuals with longer telomeres generally lived longer.
Hammers: ‘Until recently we thought that an individual’s telomeres got shorter at a constant rate, and that it was thus possible to use telomere length as an internal clock to measure the calendar age of organisms in the wild.’
Although telomeres do get shorter as you get older, the rate at which this happens varies from individual to individual. That is because different individuals are exposed to different amounts of biological stress during their lives. ‘Telomere length is thus more of a measure of the total amount of damage that someone has suffered during his or her lifetime’, says Hammers.
That idea had already been investigated in a laboratory setting, but never before in the wild. ‘It’s virtually impossible to do this kind of research on people’, say the researchers. ‘That would not only take a lot of time, but we also usually intervene when people get ill. Then it would no longer be research under natural conditions.’
Telomeres appear to be a reflection of the oxidative stress an individual suffers during his or her lifetime. The healthier you are, or have been, the better shape your telomeres are in. But what exactly lies behind this is difficult to ascertain. We do know that telomeres are attacked by oxidants. Things like smoking, eating unhealthily or exposing your body to extreme physical or mental stress all lead to your telomeres becoming shorter.
More information: Martijn Hammers
Telomere length and dynamics predict mortality in a wild longitudinal study, David S. Richardson, Emma Barrett (Universiteit East Anglia), Terry Burke (Universiteit Sheffield), Jan Komdeur, Martijn Hammers (Rijksuniversiteit Groningen). Molecular Ecology, 20 november 2012.
The research was conducted in collaboration with the conservation group Nature Seychelles.
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