Winter has officially arrived, and for many Brits this also brings a case of the winter blues.

SAD is the acronym for Seasonal Affective Disorder, a form of depression that usually begins in autumn, continuing through the winter months, and believed to affect up to 10% of the population. Symptoms include feeling sad or anxious, fatigue, concentration problems, irritability and feelings of guilt and hopelessness.

The role of sunlight

Although the exact cause of SAD isn't clear, a number of studies suggest it may be triggered by lack of sunlight.

One hypothesis is that reduced sunlight exposure interferes with the body's biological clock that regulates mood, sleep and hormones. Another theory is that lack of sunlight causes an imbalance of neurotransmitters such as dopamine and serotonin which regulate mood.

Link between vitamin D and depression

It is well known that vitamin D levels in the body fluctuate with the changing seasons in response to the amount of sunlight. Vitamin D plays part in the synthesis of both dopamine and serotonin, and it is logical that there is a relationship between vitamin D and symptoms of depression.

You may be at a greater risk of vitamin D deficiency if you stay mostly indoors for health, work or other reasons, have naturally dark skin, or avoid the sun for skin protection or due to medical reasons. Where you live is also a factor, and our Tasmanian Medical Laboratory reports that 60% of Tasmanians presenting for the first time for vitamin D testing at the end of winter show deficiency, and on average in any season of the year 44% of Tasmanians are vitamin D deficient.

Combatting SAD

So if you feel you've got a case of the 'sads', then you might want to consider:

• increasing your exposure to sunlight (NB following safe sun guidelines)
• increasing dietary calcium
• increasing physical activity
• taking a vitamin D supplement

If you're worried you may have a vitamin D deficiency, then finding out is easy with a simple blood test - see our Vitamin D Check for more details.