A MAJOR study is under way in Southampton into the winter blues.

The syndrome - Seasonal Affective Disorder (SAD) - affects an estimated 500,000 people in Britain annually.

Patients at two GP surgeries in the city will be invited to take part in the programme to establish how widespread the problem is.

The study is being led by Southampton University's SAD research centre run by Professor Chris Thompson, head of the Department of Mental Health.

SAD strikes between September and April, in particular during December, January and February.

It is caused by a biochemical imbalance in the brain due to shortening of daylight hours and lack of sunlight during winter months and can have devastating effects on the lives of sufferers.

The university and SAD Association are funding the four-month study.

Professor Thompson has devised a diagnostic questionnaire that is being given to 5,000 patients in the waiting rooms of the two Southampton surgeries plus two in Basingstoke.

Professor Thompson said: "For many people SAD is a seriously-disabling illness preventing many from functioning normally for 40 per cent of their lives.

"Personal relationships tend to suffer and there have been cases of suicide. Yet there is a very efficient, cost-effective treatment that does not involve drugs."

Therapy involving exposing sufferers to bright light under special light boxes is offered at the Southampton research centre, which sees patients referred from across the country.

The therapy works in up to 85 per cent of cases but the £200 boxes are not available on the NHS.