Surrogate Endpoints and Aging Biomarkers in Trials

What a surrogate endpoint is

The US Food and Drug Administration (FDA) describes a surrogate endpoint as a clinical trial endpoint used as a substitute for a direct measure of how a patient feels, functions or survives. It does not measure the benefit of interest itself. It is only expected to predict that benefit. [1]

A biomarker is a defined characteristic that is objectively measured as an indicator of normal biological processes, disease processes or responses to an exposure or treatment. Only some biomarkers become surrogate endpoints. [1]

How a biomarker earns trust

FDA says surrogate endpoints sit on a ladder of validation. [1]

FDA gives blood pressure and stroke as an example of a validated pair: many trials of different blood pressure medicines showed that lowering systolic pressure lowered stroke risk. [1] FDA also says that before a surrogate can replace a clinical outcome, extensive evidence must accumulate, including epidemiological studies and clinical trials. [1]

Two other points matter. FDA distinguishes biomarkers from clinical outcome assessments, which describe how a person feels or functions or how long the person lives. [1] And FDA notes that products approved on a "reasonably likely" surrogate need follow-up data after approval to find out whether the surrogate really predicted benefit. [1]

Where aging biomarkers stand

A 2023 framework paper in the journal Cell said the field lacks standards and consensus on the properties of a reliable aging biomarker, and that this hinders development and validation for clinical use. [2] A 2024 survey of experts in Nature Aging found that clinical translation of aging biomarkers remains limited and named six key barriers. Its recommendations included linking biomarkers to clinically useful insights and validating markers that are robust at the level of individuals, not only groups. [3]

A 2025 review in Physiological Reviews made a related point. It said validation in humans has been held back by the limited translation of results from model organisms and by the lack of robust biomarkers that could shorten trials. It added that biomarkers based on function, resilience and frailty are available now and have proven predictive value for illness and death, while molecular markers hold promise for the future. [4]

Put plainly: at the time of writing we found no source showing that an epigenetic clock, telomere length or any single molecular "age" marker has been validated as a surrogate for longer life or better health in people. Label: insufficient evidence for use as a trial surrogate. We read FDA's surrogate-endpoint guidance page, which does not mention aging; we did not review FDA's full surrogate endpoint table or its biomarker qualification list, so check those directly. [1]

Why this matters for common claims

• "It lowered my biological age." A test score moving is a biomarker change. See biomarkers and biological age tests and epigenetic clocks.
• "It raised NAD+ levels." Raising a level in blood does not show better health. See NAD+, NMN and nicotinamide riboside.
• "It extended lifespan in mice." That is preclinical, and a lifespan result in animals is not a surrogate for people. See mouse lifespan studies.
• Biomarker change versus meaningful outcome. See the biomarker changes versus health outcomes guide for the general idea.