There is little doubt that when the sun is shining we feel happier, have more energy and experience a more positive attitude. But when the evenings and mornings are dark and the weather takes a turn for the worse, our mood can easily be affected.
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Many of us will feel more lethargic, less sociable and low during the winter months, but while plenty experience a touch of the winter blues, for some the mood alters more severely.
The NHS estimate that around seven per cent of the population suffers from Seasonal Affective Disorder (SAD). This kind of depression changes with the seasons.
Also known as "winter depression", the symptoms tend to be more obvious during the winter and it often begins as the days become shorter during the autumn.
Generally it is at its worst during December, January and February and, for most people, the depression begins to lift come spring.
So are you just blue or is there more to it?
The symptoms of SAD are similar to those of other types of depression - lethargy and fatigue with a lack of interest in day-to-day living, sleep problems, anxiety, irritability, difficulty concentrating and over eating.
The condition can also affect libido, with many sufferers losing interest in sex during the winter months. For a small percentage of people, the symptoms become so severe that they require continuous treatment to function throughout the winter.
According to the NHS it tends to affect younger people, often those in their twenties, but it can begin at any age and children who display irritability, bad behaviour or tiredness may also be suffering.
But there is help available. Unfortunately, there are only a few SAD clinics in the UK but your GP may be able to recommend treatment.
Bright light therapy is often the most effective treatment. According to the mental health charity Mind, phototherapy, as it is called, helps around 80 per cent of people, usually within three to five days.
The range of equipment is growing by the day and light boxes, visors and dawn simulators are among those that enable SAD sufferers to continue their own treatment throughout the winter months.
However, manufacturers recommend trying phototherapy early in winter, as it may not offer relief to those whose symptoms are already severe.
Talking treatments can also be useful - counselling, psychotherapy or cognitive behaviour therapy may help to find the factors that contribute to depression and thereby enable SAD sufferers to overcome their problem.
In severe cases, antidepressants are prescribed and those that increase serotonin levels, such as Prozac, have proved successful.
For those displaying milder symptoms, it is important to make the most of the daylight. Go outdoors when you can, especially when the sun is at its brightest and, if possible, avoid making important changes to your life (changing jobs or moving house) that can add to stress.
SAD is a form of depression - if you are struggling to cope with the symptoms, your GP may be able to refer you for talking treatments or prescribe antidepressants. Alternatively visit www.sad.org.uk for more information.