Why do your telomeres get shorter as you age?
Telomeres shorten because the copying process during cell division cannot fully reproduce the ends of chromosomes, and the repair enzyme telomerase is switched off in adult body cells. Stress and oxidative damage can accelerate that process further, but the fundamental mechanism is unavoidable as long as cells divide.
With every cell division, the copying enzyme cannot reproduce the very last segment of a chromosome. That may sound like a minor flaw, but the losses add up: roughly 50 base pairs per division, and after dozens of divisions thousands of base pairs have been lost from the telomere. The enzyme that could repair this loss, telomerase, is active in humans only during the first few weeks after fertilisation. After that, virtually all cells in the body switch it off, with the exception of stem cells and germ cells.
On top of that copying problem, enzymes actively nibble away a small piece of the DNA strand at the tip. This probably accelerates the loss considerably, although the exact extent has not yet been precisely measured. And occasionally a telomere suddenly loses a large chunk all at once, due to an error in the loop structure of the telomere or an unfortunate exchange between chromosome copies. These sudden jumps are rarer, but can cause chromosomal instability.
Living conditions also play a role. Chronic psychological stress and oxidative damage, caused by harmful oxygen molecules as a result of inflammation or environmental factors, are associated with faster telomere shortening. The biological pathways run through stress hormones and increased cellular damage. These are associations that have been demonstrated in humans and in cell systems; whether stress shortens telomeres directly or through other routes has not yet been fully established.
When a telomere becomes too short, the cell registers this as a kind of break in the DNA. The cell then stops dividing or shuts itself down. This is the price the body pays for the absence of telomerase: signs of ageing increase. At the same time, there is a flip side: it is precisely because of this halting of cell division that the body partially keeps uncontrolled cell growth, and therefore cancer, in check. People who are born with relatively short telomeres already start from a lower baseline, partly due to heredity and prenatal conditions.
This answer is based on several broad review articles of the scientific literature on the mechanisms of telomere biology. The copying problem and the absence of telomerase are well-supported, causal mechanisms. The role of enzymatic degradation at the telomere end is plausible but less precisely quantified. The associations with oxidative stress and psychological stress have been demonstrated in both cell systems and human studies, but cause and effect have not yet been conclusively established there.
What does telomerase do to the length of your telomeres?
Telomerase keeps telomeres intact for longer by compensating for shortening during cell division, but in most body cells the enzyme is barely active, causing telomeres to shrink over time.
Can you lengthen or restore your telomeres?
Healthy adult body cells cannot lengthen their own telomeres, and no proven safe way to do so from the outside yet exists. Be sceptical of supplements or therapies that promise otherwise.
Why do some cells stop dividing as you age?
Cells stop dividing because their chromosome tips wear down and they accumulate DNA damage: a protective mechanism that in later life becomes harmful precisely because the stalled cells build up. Treatments that address this are still under active investigation and are not ready for self-application.
How do telomeres protect your DNA?
Telomeres protect your chromosome ends through a system of proteins that simultaneously prevents false alarms and harmful fusions. If that system fails due to inherited defects, you can develop serious ageing-related diseases.
Can you lengthen your telomeres through lifestyle?
Lifestyle can probably slow telomere shortening, but the starting length of your telomeres is largely genetically determined and by far the strongest predictor of how quickly they shorten. Not smoking, exercising regularly and following a Mediterranean diet are the most well-supported steps you can take.
What are telomeres and can I keep them longer?
A healthy lifestyle, regular exercise, stress reduction and adequate vitamin D appear to slow telomere shortening, but anyone looking for a quick fix will not find one: the science is not there yet.