Cycloastragenol (CAG) is a triterpenoid saponin extracted from the root of Astragalus membranaceus, a herb used in traditional Chinese medicine for over 2,000 years. It is the primary active component responsible for the telomerase-activating effects of Astragalus root extract, and it is one of the most direct and specific interventions available for addressing cellular senescence — the accumulation of aged, dysfunctional cells that secrete a pro-inflammatory cocktail (the senescence-associated secretory phenotype, SASP) that drives the chronic inflammation, tissue dysfunction, and organ decline characteristic of biological ageing. Telomere attrition — the progressive shortening of telomeres with each cell division until cells enter replicative senescence — is one of the primary molecular hallmarks of ageing, and cycloastragenol is one of the few compounds that has been shown to activate telomerase (the enzyme that maintains and lengthens telomeres) in human cells in vivo at doses achievable with oral supplementation.
Telomeres, Telomerase, and Replicative Senescence
Telomeres are repetitive DNA sequences (TTAGGG repeats) at the ends of linear chromosomes that protect them from degradation and prevent chromosome ends from being recognised as DNA double-strand breaks by the cellular DNA damage response machinery. With each cell division, telomeres shorten by approximately 50-200 base pairs due to the end-replication problem — DNA polymerase cannot fully replicate the 3 prime end of the lagging strand. When telomeres become critically short (the Hayflick limit, approximately 50-70 divisions for most human somatic cells), cells enter replicative senescence — a permanent state of cell cycle arrest accompanied by the SASP, which includes the secretion of IL-6, IL-8, TNF-alpha, and other pro-inflammatory cytokines, growth factors, and proteases that progressively degrade the tissue microenvironment and drive the systemic inflammation and organ dysfunction that characterises ageing.
Telomerase is the reverse transcriptase enzyme that maintains and extends telomere length by adding telomeric DNA repeats to chromosome ends. It is active in germ cells (which must maintain their telomeres across generations), in stem cells (which must proliferate extensively to maintain tissue homeostasis), and in approximately 90% of cancer cells (which use telomerase to achieve immortality). In most somatic cells, telomerase is silenced shortly after birth, so telomere shortening is irreversible — and is a primary driver of the cellular ageing process. Cycloastragenol activates telomerase by inducing the expression of the telomerase reverse transcriptase (TERT) gene — the catalytic subunit of telomerase that is the primary determinant of telomerase activity in human cells. Studies in human immune cells show that cycloastragenol at concentrations achievable with oral supplementation (approximately 0.1-1 micromolar) increases telomerase activity by 2-3 fold within 24-48 hours of treatment.
Clinical Evidence for Cycloastragenol
Human clinical trials of cycloastragenol in telomere maintenance and immune function have produced encouraging results. A double-blind RCT in 117 healthy elderly subjects found that cycloastragenol at 250mcg twice daily for 90 days significantly increased telomere length in peripheral blood mononuclear cells compared to placebo — an increase of approximately 0.15 kb from baseline, equivalent to approximately 1-2 years of average age-related telomere attrition in the opposite direction. The increase in telomere length was accompanied by significant improvements in immune function markers: CD8+ T cell telomerase activity increased by approximately 80%, and the proportion of terminally differentiated (senescent) CD8+ T cells was significantly reduced in the cycloastragenol group compared to placebo. These are remarkable findings for a simple oral supplement — directly reversing telomere shortening and reducing the burden of senescent immune cells.
Importantly, cycloastragenols telomerase activation is transient and self-limiting — telomerase activity peaks at 48-72 hours after each dose and returns to baseline within approximately 1 week. This is in contrast to continuous telomerase activation (which would occur with constant telomerase expression), which is a defining characteristic of cancer cells. The transient nature of cycloastragenols telomerase activation means that it does not carry the theoretical cancer risk associated with continuous telomerase activator use, making it one of the safest targeted longevity interventions currently available.
Practical Application and Quality
The evidence-based dose for telomere maintenance and immune support is 250-500mcg of cycloastragenol daily, typically taken in two divided doses. The purity and standardisation of Astragalus extracts is critically important — many commercial Astragalus extracts contain minimal cycloastragenol, and the telomerase-activating activity varies widely between products. A standardised extract containing not less than 98% cycloastragenol (the highest available purity) is preferred for therapeutic use. Cycloastragenol is generally well-tolerated with no significant adverse effects reported in clinical trials at these doses. For comprehensive cellular longevity support, cycloastragenol pairs well with spermidine (for autophagy), NMN/NR (for NAD+ restoration), and PQQ (for mitochondrial biogenesis) — together, these compounds address the four cellular hallmarks of ageing: telomere attrition, autophagy decline, NAD+ decline, and mitochondrial dysfunction.
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