MENTAL HEALTH ∙ 4 minutes read

Seasonal affective disorder: causes, symptoms and treatments

By Kirsty Mason | Medically reviewed by Danielle Brightman

Seasonal affective disorder (SAD) is a type of depression that’s determined by the seasons and is particularly common during the winter months. Although we’re still getting to grips with what causes SAD, it’s thought that daylight affects our mood in all sorts of ways. With colder weather and more darkness, our bodies make a biological shift - and this could have a negative impact on mental health.

Noticing changes as we move towards winter doesn’t necessarily mean that you have seasonal affective disorder. It’s normal to experience small changes in sleeping, eating and social behaviour over the winter months. As the window of daylight is narrowed, our bodily systems are disrupted in several ways.

When it comes to biological functions, the seasons drive the following changes:

  • Hypothalamus: The hypothalamus is a small region of the brain that is critical for keeping the body in a state of homeostasis (where feelings such as hunger and temperature are balanced). When the body is out of balance in some way, it signals the hypothalamus. The hypothalamus will then release the correct hormones to trigger a reaction in the body. Thus, helping it to return to a balanced state. For example, when we’re cold, the hypothalamus is signalled, which will trigger the release of hormones that cause the body to shiver and create its own heat. It’s an important function for the regulation of sleep, appetite and mood. It’s been theorised that daylight plays a role in the functioning of the hypothalamic region, especially when it comes to mood. This means that when there’s a lack of daylight, the mood isn’t regulated in the way that it should be.
  • Circadian rhythms: Circadian rhythms are biological processes (physical, mental and behavioural) that respond primarily to lightness and darkness. Functioning on a 24-hour cycle, it’s important for the regulation of sleep, appetite and mood. Lack of sunlight can disrupt the normal circadian pattern, which could unsettle mood.
  • Biological clock: The body has a natural timing device that regulates circadian rhythms (an internal process that responds to the environment). Natural daylight helps to manage sleeping patterns and informs the body when to wake up. This is why it’s difficult to get up in the morning when it’s still dark. The low light levels in winter can irritate your sleeping pattern and make you feel more fatigued throughout the day, leading to symptoms of SAD.
  • Serotonin: A lack of daylight leads to lower levels of serotonin as it’s thought that sunlight could stimulate the production of the crucial hormone. Serotonin is important for the regulation of mood and low levels of the hormone have been linked to depression.

Changes to our biology (as described above) lead to the following changes in bodily functions: 

  • Sleep: As circadian rhythms respond to light, the body’s natural sleep cycle is disrupted by longer hours of darkness. So, in winter, you might find it’s much harder to get up in the morning and you sleep for longer. Dark days could also make you feel tired and long for a nap.
  • Appetite: In winter, you might notice an increased appetite. There are several possible explanations as to why this is. For one, the reduction in serotonin levels that come from a lack of sunlight could lead to carb cravings. The consumption of carbohydrates leads to the release of insulin which results in a rise in serotonin levels. An appetite for carb-loaded foods might be driven by the need for a serotonin-hit. Alternatively, seasonal hormone changes might induce a change in hunger levels. 
  • Mood: Low levels of serotonin have been linked to depression and a lack of sunlight may cause a drop in the hormone. Disruption of circadian rhythms could also lead to depression.

Many people experience minor changes in their sleep, mood and eating habits over the colder months but if you’re experiencing more severe symptoms, such as fatigue or low mood, then you might have seasonal affective disorder.

Symptoms of seasonal affective disorder include:

  • Low mood
  • Fatigue
  • Irritability
  • Anxiety
  • Sleep problems
  • Low libido
  • Lack of enthusiasm
  • Depression
  • Overeating
  • Stress

If you think you have SAD, you should visit your GP, where they can carry out an assessment. There are also steps you can take to improve your mood if you’re feeling low. 

Tips that could help you to combat seasonal affective disorder include:

1. Spend time outdoors

Even though the sun might not be shining, get as much natural light as possible. This will give the skin a chance to absorb vitamin D, which is a critical nutrient for the body and can help to boost immunity. It can also boost your levels of serotonin, improving your mood. Sit near windows when possible and make the most out of the daylight hours.

2. Try light therapy

The NHS recommends light therapy to combat seasonal affective disorder. This is where a special light box simulates the effects of sunlight, providing the body with the benefits that lag in the winter months.

3. Eat a healthy diet

Eating a balanced diet packed with vitamins and nutrients will help to balance your mood and increase the activity of serotonin. Avoid foods that are high in sugar as, after an initial boost, the high sugar content will cause you to crash. If you struggle to stick to a healthy diet, try following our 7-day high cholesterol diet plan or 7-day acid reflux diet plan

4. Exercise

Exercise is a powerful mood booster. This is because it triggers the release of endorphins and other feel-good chemicals in the brain. Even taking a walk outdoors can help to improve your mood.

Regular exercise also reduces your risk of health issues such as diabetes, cardiovascular disease and cancer.

5. Speak to your doctor

It’s important to seek help if you’re showing symptoms of seasonal affective disorder. Visit your local GP where they can carry out an assessment and advise you on the next steps.

The bottom line

Seasonal affective disorder is particularly common in the winter and can cause symptoms such as low mood, anxiety and depression. Although it’s unclear exactly what causes the change in mood, it’s thought that daylight has a big role to play and can influence the biological functions of the body. If you’re suffering, it’s important to speak to your doctor and seek treatment. 

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