People who have seasonal affective disorder can be helped by exposure to special 'light boxes' (we all benefit from higher light levels at home and exposure to the sun for other reasons). For people who have had one episode of depression, the best way to avoid another is to stay on antidepressant medication.

Social factors are important too. Friendships, family relationships and purposeful activity are our best defence against depression. Anything that enhances mood and self-esteem is also worth doing, whether that is luxuriating at the hairdresser's, having a face-lift, taking up painting, buying a kitten or trawling the Internet for new friends. In retirement, we need to replace the stimulus, purpose and companionship that paid work and young families offered.

Depression and heart health

Researchers are increasingly convinced that there is a link between the health of our hearts and arteries and depression. In recent studies many people who developed depression later in life were found to have blood vessel damage in their brains. We're used to the idea that we should look after our cardiovascular system to prevent heart disease and stroke, but this evidence suggests that it's a good idea to keep our arteries in top condition for our mental health too.