Scientists say those who age best have a light-hearted, optimistic outlook on life.

The findings offer a new theory on why some people with good genes have a sunnier outlook and sharper mind in old age, with exercise and even completing crosswords previously cited as ways of keeping your brain young.

However, scientists at the University of Hamburg in Germany discovered that simply focusing your brain on positive thoughts, and living for the moment, rather than looking too far into the future, can help maintain good mental health.

Dr Stefanie Brassen, the study’s author, said that successful ageing came down to ‘the positivity effect