But why should there be a correlation? As Goodwin explains: “The drive for exercise is absolutely embedded in the brain over 1.5 million years of evolution from when we were hunter-gatherers.” Because our survival depended on our ability to track and kill animals for food by tiring them out, our physiology developed to support long purposeful treks – “to walk quickly for long periods of time and not get fatigued.” He says: “The relationship between adequate brain function and exercise is fundamental.”

This also partly explains why a sedentary life is so bad for brain health. Between hunting, people had to rest – and, says Goodwin, “the brain rested as well to conserve energy. If we’re inactive, we have an inactive brain. It’s an energy-saving strategy. That’s how we evolved, an intense relationship between hunting and gathering, and activity, and brain health.”

He adds: “People who are inactive have a higher risk of high blood pressure, of high blood glucose, high fat content in the body, especially around the waist, and high cholesterol – or what’s called metabolic syndrome, a collection of recordable measurements which tells us we’re at risk of chronic long-term illness. Exercise reduces the risk of those features appearing.” And by keeping your blood pressure low, blood sugar low and the fat round your waist down, not only will you reduce your risk of chronic long-term illness, you will also increase your brain health, he says.

Conversely, he notes that our mortality rate increases by 2 per cent for every hour of sitting, and by 8 per cent where we’re on our backside for more than eight hours per day. Plus, studies have shown that sedentary behaviour is a predictor of Alzheimer’s. Goodwin advises “waging war on the chair”, taking a 10-minute movement break at least every 50 minutes, and making it a rule never to sit when you can stand.

But not only can we slow ageing by moderate exercise, we can turn back the years. “If you do enough moderate to intense exercise, you can reverse the ageing of the brain,” says Goodwin. He points to research by scientists at the University of Pittsburgh. Professor Kirk Erickson and his team recruited 120 sedentary older people (without dementia) and divided them into two groups. One walked around a track for 40 minutes a day, three days a week, the other did stretching exercises.

At the end of the one-year study, says Goodwin, the moderate exercisers experienced improvements in memory and brain health. “Parts of their brain, notably the hippocampus, increased in volume by 2 per cent.” (The stretchers, meanwhile, sadly experienced a decrease in hippocampus volume by about 1.4 per cent.)

Boosting neurogenesis also has a positive impact on our cognitive reserve. “If you have a mentally demanding occupation, if you are well-read, if you continue your education and you tax the brain continuously throughout life, the brain develops all these networks of connections between the synapses, which temper the effects of Alzheimer’s,” says Goodwin. “The growth of new brain cells enables better resilience and better cognitive reserve. They work hand in hand.”