Can you lengthen or restore your telomeres?
Fully restoring or lengthening telomeres has not yet been demonstrated in humans. Vitamin D3 (2000 IU/day) did measurably slow shortening in a large study. Fish oil had no effect, and artificially lengthening telomeres also carries cancer-related risks.
Fully restoring telomeres is not yet possible in humans. What does appear to work is slowing their shortening. In the VITAL study, a rigorous placebo-controlled trial with more than a thousand participants followed for four years, telomeres in people who took 2000 IU of vitamin D3 daily shortened by an average of 140 DNA letters less than in the placebo group1. The telomeres did not actually grow longer, but they wore down more slowly. That difference was measured with statistical reliability.
Fish oil supplements (1 gram per day, for four years) had no measurable effect on telomere length in that same study, neither after two years nor after four years. On the basis of this solid research, fish oil can be ruled out as a means of slowing telomere shortening.
How long your telomeres are is largely determined at birth. Research involving 147 people showed that the differences in length between individual chromosome ends can amount to more than 6,000 DNA letters, and that this relative order remains stable as you age2. Genetics therefore plays a major role, independent of your lifestyle.
Artificially lengthening telomeres sounds appealing, but has a downside. In 416 children with neuroblastoma, tumours that actively maintained their telomeres were associated with poorer survival3. Tumours without that telomere maintenance had a favourable prognosis. Telomere lengthening therefore helps cancer cells remain immortal. As long as cancer cells and normal cells cannot be treated separately, 'boosting telomeres as an anti-ageing strategy' is risky.
Lifestyle factors such as smoking, excessive alcohol consumption and prolonged exposure to UV radiation increase oxidative stress and thereby accelerate cellular ageing, independently of your genetically determined telomere length. This has been demonstrated in laboratory studies using human cells. Translating those findings to the whole body requires caution. Telomere length is, moreover, only one piece of the ageing puzzle; scientists recommend looking at multiple biological markers together.
Based on published studies, including one large placebo-controlled study (VITAL, n=1031, PMID 40409468), one large observational tumour study (n=416, PMID 30523111), a measurement study in humans (n=147, PMID 38603523), and multiple laboratory and review studies. No meta-analysis was used as a direct source.