Memory loss and growing mental incapacity used to be seen as inevitable consequences of ageing. Now we talk of dementia as an illness that could possibly be cured or prevented. The incidence of new cases of dementia is falling. A survey in the UK in 1994 revealed roughly 650 000 cases of dementia. With a subsequent increase in the average age at death, a survey in 2013 should have found nearly 900 000 cases, but in fact the total was less than 700 000. Why should this be so? Over the same period rates of heart disease have fallen, and in general the health of the blood vessels of the elderly has improved. Given that brain function requires the supply of oxygen to the brain from blood vessels, the improvement in the health of blood vessels …