At present there is no sure way to prevent dementia, but scientists are gradually finding out some ways of making it less likely. Generally, the lifestyle factors that keep us healthy earlier in our lives are the same ones that may help us to avoid, or at least delay, dementia and Alzheimer's later on. In other words: plenty of exercise and fresh air, a varied diet with plenty of fruit, vegetables and grains and enough sleep will not guarantee that you don't develop dementia, but these things are our best chance at the moment.

There are also social and personality factors. Again, there are no guarantees, but people who have a lot of friends and interests seem to stay mentally alert for longer. There does seem to be a link between brain stretching activities - doing puzzles or learning a language, say - and better mental health in old age. The latest research even seems to suggest that people who move slowly or have a weak hand grip in middle age are at increased risk of dementia - though there could be any number of reasons for that. Anyway, if you remain alert and interested in life, have friends and look after yourself, you are doing all you can.