Does your telomere length tell you anything useful about your health?

Telomere length is not a simple health thermometer. A longer telomere is not necessarily better: genetically longer telomeres robustly increase the risk of 24 types of cancer, most strongly for bone cancer, glioblastoma and thyroid cancer. Shorter telomeres, on the other hand, are associated with a higher risk of heart disease, chronic kidney disease, rheumatoid arthritis and idiopathic pulmonary fibrosis. It is therefore a two-sided relationship: too short is bad for one set of conditions, too long is bad for another.

How strong is the evidence for this? The associations come from genetic research in which inborn variants serve as a 'natural experiment', which provides a stronger indication of causality than simple correlation studies. Yet there is also older genetic research suggesting that telomere length is more often a consequence than a cause in most diseases. That contradiction has not yet been fully resolved.

A measurement of your telomere length in blood also does not tell the whole story about the rest of your body. The correspondence between blood telomeres and those in other tissues is moderate: the correlation averages around 0.58, and is even lower when you compare blood with tissue that does not derive from blood. What your telomere test shows therefore reflects only a limited picture of what is happening in your brain, lungs or intestinal cells.

Can you favourably influence your telomere length? One large randomised trial found that vitamin D3 (2000 IU per day for four years) significantly slowed telomere shortening: on average 140 base pairs less loss compared with placebo. That is statistically demonstrable but small in absolute terms. Fish oil (1 gram per day) had no measurable effect on telomere length in the same trial. Prolonged obesity from childhood or adolescence was associated with faster telomere shortening as early as age 28-31, underscoring the importance of a healthy weight from an early age.

Telomeres also play a fundamental role in cancer: mutations in the gene that controls telomere production (TERT) have been found in more than 50 types of cancer, allowing cancer cells to keep dividing indefinitely. In rare inherited variants of that same gene, people develop a specific blood disorder (myelodysplastic syndrome) on average seven years earlier and have poorer survival after stem cell transplantation. This concerns a small group of patients, but it shows that telomere biology can be medically relevant for people with a family history of early blood disorders.