Seasonal Affective Disorder

Seasonal Affective Disorder (SAD) is a type of depression that comes and goes in a seasonal pattern. Often referred to as ‘winter depression’, this is because SAD often affects us during the colder darker months of the year where symptoms appear more severe.

What causes SAD?

While the exact causes of Seasonal Affective Disorder aren’t fully understood, it is generally accepted by the NHS and NICE advice that it may have something to do with experiencing reduced exposure to sunlight during the winter months. This affects a part of the brain called the hypothalamus that produces many essential hormones, causing several potential problems for the body.

The body may produce higher levels of melatonin, a hormone which makes you feel sleepy, while also reducing the production of serotonin, hormone that affects your mood, appetite and sleep. Lower levels of serotonin are often linked to feelings of low mood and depression. A lack of sunlight may also affect the body’s internal clock which can also lead to symptoms of SAD.

Sunlight is also required for the production of essential vitamin D in the body, so it is no surprise that vitamin D deficiency has long been linked to the symptoms of Seasonal Affective Disorder. One theory for this is that many vitamin D receptors are found in areas of the brain that have also been linked to depression.

Symptoms of SAD

The symptoms of SAD are very similar to those of normal depression, the only difference being that the feelings of depression usually disperse on their own when the spring and summer months arrive. The symptoms will vary from person to person, with some experiencing only mild symptoms, while for others it can severely impact their day to day life.

According to the NHS, signs that you may experiencing SAD include a persistent low mood, lack of pleasure or interest in your usual pursuits, feelings of despair, guilt, insignificance, stress and anxiety, low self-esteem and a reduced sex drive. You may also find yourself being less social and experiencing feelings of irritability and tearfulness.

In addition to this you may also find that you feel more lethargic than normal and that you sleep for longer, finding it hard to wake in the morning. Because of this you may find concentrating more difficult and you may be less active than you normally are. You also may find you have an increased appetite for foods containing carbohydrates, leading to weight gain.


If you believe you may have Seasonal Affective Disorder, then it is important that you make an appointment with your GP or physiotherapist for a diagnosis and treatment advice. However, NICE guidelines recommend treating the symptoms of SAD in the same way as other types of depression, for which there are also several options that you can try yourself.

One thing you can do is to try and get as much sunlight as possible by being active outdoors and making your home and work environments as light and airy as possible. Taking regular exercise and eating a healthy balanced diet are also proven positive ways to lift your mood, and it is recommended that you try to avoid stressful situations as much as possible. It is also important to seek support from you family and friends when you are experiencing symptoms of depression.

Your GP may also refer you to a course of cognitive behavioural therapy (CBT) and counselling. CBT is based on the theory that the way we behave and think affects our feelings and so will aim to change the way you think about situations and what you do about them. This therapy can take many different forms and a trained therapist will ascertain the course best for you. Likewise, counselling will involve talking about your worries and feelings and your past experiences.

Light therapy is another course of action that some people with SAD have found helps boost their mood. This involves sitting in front of a special lightbox for a period of 30 minutes to an hour every morning, which is thought to replace the sunlight you are missing in the winter months. Most people can use light therapy safely, but it is not available on the NHS so you have to purchase the light box yourself. While there is mixed evidence regarding the effectiveness of the treatment, many regard it as a short term measure to relieve the symptoms of SAD.

Vitamin D supplementation can make an important difference to how you feel, especially if you suffer with chronic pain or muscle aching, combined with low mood. Taking between 700 and 1500iu’s is suggested unless you are severely vitamin D deficient. If you feel you may be severely deficient you can ask your GP for a blood test and you may be prescribed a loading dose of around 10-20,000iu’s per day for a short period of time.