Seasonal affective disorder

Seasonal affective disorder

In the UK, our clocks went back an hour last night. Summer is officially over, autumn is upon us and we are moving into winter. Many of you may be enjoying the fresh mornings wrapped up in cosy jumpers indulging in hot chocolates, but the shorter days and longer hours of darkness can make life a real struggle for some people.

It’s totally normal to feel happier and more energetic during the longer summer days, and feel that you want to stay cocooned in your duvet and sleep-in longer during the winter months. However, some people experience these dips in mood a lot more intensely than others.



What is seasonal affective disorder?

Seasonal affective disorder (SAD) is a unique type of mental health disorder and some call it the “winter depression”. As the name suggests, the time of year has a significant impact on a person’s general mood and energy levels, with symptoms similar to depression. It causes feelings of despair, irritability, heightened carbohydrate cravings and a loss of enjoyment in daily activities.


“It’s as if my mood turns grey the same time as the sky”

– Mind UK


What are the causes?

Altered body clock: As discussed in a previous blog post, our bodies have an internal clock. When light is sensed at the back of the eye on the retina, signals are sent to a region in the brain called the SCN (suprachiasmatic nucleus). The SCN then sends signals to all our others cells in our body to tells them what processes they should be carrying out. Basically, daylight tells our body we should be awake, and darkness tells our body we should be asleep, this is called our circadian rhythm. The circadian rhythm helps to regulate food digestion, appetite, energy levels, sleep, and mood. However, people with SAD are thought to have a disruption to this rhythm.

Low serotonin: Serotonin, one of the “happy hormones”, is a neurotransmitter that controls how happy we are and boosts our mood. It’s thought to be low in patients with SAD during the winter. Research shows that people with SAD have higher levels of the serotonin transporter (SERT) which carries serotonin away from the site of action. Higher levels of SERT, means lower available serotonin to induce its effects, and increased feelings associated with depression are experienced.

High melatonin: Melatonin is another neurotransmitter, but it affects our sleep quantity and quality as well as our mood. Normally, melatonin is inhibited during the day, and as it gets darker its production increases. This is why we feel sleepy at night-time. Patients with SAD produce melatonin at higher levels disrupting how awake they are during the day.


What can help to alleviate SAD?

The aim is to get better hormonal regulation. Here’s a few options:

  • Lightbox therapy: A lamp emitting the same wavelength of light as the sun. They artificially extend the photo period (amount of light) in your day. This helps to suppress melatonin production.
  • Diet high in tryptophan: Tryptophan is an amino acid and it’s a building block for serotonin. More tryptophan = more serotonin production. Foods such as turkey, chicken, tuna, salmon and seeds are high in this amino acid.
  • Regular exercise: Exercise decreases stress levels via increasing serotonin levels.



Click on the links below for a little more reading if you wish…

1.  Molecular mechanisms controlling the circadian rhythm. Click here.

2. Seasonal difference in brain serotonin transporter binding predicts symptom severity in patients with seasonal affective disorder. Click here.

3. The Effects of Dietary Tryptophan on Affective Disorders. Click here.

4. Bright-Light Therapy in the Treatment of Mood Disorders. Click here.



For more of my science posts, click here.



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