Table 1.

Criteria for a biomarker of ageing process

I	It must predict the rate of ageing. In other words, it would estimate where a person is in their total lifespan. Operationally, it must be a better predictor of lifespan than chronological age alone.
II	It must monitor a basic process that underlines the ageing process, not the effects of diseases.
III	It must be able to be tested repeatedly without harming the person, for example, a blood test or an imaging techniques.
IV	It must be something that works in humans and in laboratory animals, such as mice. This is so that it can be tested in laboratory animals before being validated in humans.