This is the 90th instalment in a series on dementia, including the research into its causes and treatment, advice for carers, and stories of hope

Not long ago, Dr Kevin Tran, founder of The Phoenix Community for carriers of the APOE4 gene – the “Alzheimer’s gene” – like himself, noted that we need to look after our brain as if it were the only car we would ever own. We must tend to its bodywork, provide regular maintenance and keep up with services so that it runs for as long as we need it to.

His analogy is even more apt alongside the emergence of “MileAge”, a metabolomic ageing clock that estimates biological age from a blood sample, developed by Dr Julian Mutz and his team at King’s College London in the UK.

Mutz named the clock MileAge because he liked the car comparison. A vehicle’s chronological age matters, but its wear and tear, indicated by mileage, is often equally important.

Think of it like this, Tran says: two cars leave the factory the same year, but one is a wreck by 100,000 miles while the other still runs beautifully. The difference was never the model year. It was the mileage and how it was driven. Your body is the same. Your birthday is the model year. Your metabolic markers are the real mileage, and a clock like MileAge puts that number on the dashboard.

The hopeful part? Unlike a car, you can wind your biological mileage back by changing a few habits.