Understanding seasonal affective disorder (SAD)

SAD is depression with a seasonal pattern. You might have heard about it in connection to winter. But you can experience it at any time of the year. 

In the weeks before the clocks go back, I start to feel sluggish and down. It's harder to keep to my morning routine of going out for a walk before breakfast because it's wet, cold and dark.

What is seasonal affective disorder (SAD)?

Seasonal affective disorder (SAD) is a type of depression that you experience during particular seasons or times of year. Depression is a low mood or loss of interest and enjoyment in things you usually do. It lasts for a long time and affects your everyday life. 

If you have SAD, you'll experience depression during some particular seasons. Or you'll experience depression because of certain types of weather or temperature.

Experiencing SAD in the winter is more well known. But you may struggle more with summer months. SAD can include any depression with a seasonal pattern.

It's common to be affected by changing seasons and weather. Or to have times of year when you feel more or less comfortable. For example, you might find that your mood or energy levels drop when it gets colder or warmer. Or you may notice changes in your sleeping or eating patterns.

But if your feelings are interfering with your everyday life, it could be a sign that you have depression. And if they keep coming back at the same time of year, doctors might call this seasonal affective disorder (SAD). They might also call it 'seasonal depression' or 'depression with seasonal pattern'. 

What are the symptoms of SAD?

If you have SAD, you might experience some of the signs and symptoms listed below. But it's different for different people, and can vary season to season. You might also have other kinds of feelings which aren't listed here.

• Persistent low mood
• Lack of energy
• Difficulty concentrating
• Not wanting to see people
• Loss of interest or enjoyment in things
• Feeling sad, tearful, guilty or hopeless
• Feeling anxious, angry and agitated
• Physical aches and pains with no obvious physical cause
• Sleep problems, for example sleeping too much or too little
• Changes in your appetite, for example feeling hungrier or not wanting to eat or craving certain foods more
• Losing interest in sex or physical contact
• Suicidal thoughts
• Moving very slowly, or being restless or agitated
• Other symptoms of depression

If you have other mental health problems, you might find that things get worse at times when you're affected by SAD.

Some other mental health problems can also have a seasonal pattern, like bipolar disorder.

I just can't stay awake and the thought of having to go out, stay awake, make conversation. I just can't do it.

Sarah's story

Sarah explains how she developed seasonal affective disorder (SAD) and what it's like living with it day to day.

See our transcript of the podcast if you would like to read rather than listen to it.

I close the curtains in the evening and wish it was dark so I could go to bed early but it's broad daylight. I need to sleep and withdraw again from the world.

What causes SAD?

The exact causes of SAD aren't clear. It's likely that a range of different things contribute to it. These can vary a lot between different people.

Research suggests that the causes are similar to causes of depression, but there are also factors which can lead specifically to SAD.

Effects of light

When light hits the back of your eye, messages go to the part of your brain that controls sleep, appetite, sex drive, temperature, mood and activity. If there isn't enough light, these functions may not work properly.

Some of us seem to need a lot more light than others. This may mean we're more likely to get SAD during the winter months.

It's like someone has switched off the light suddenly. I'm plunged into darkness, which paralyses me and keeps me pinned down to my bed.

Disrupted body clock

Your brain sets your body clock by the hours of daylight. You may hear this referred to as your circadian rhythm. One theory is that if you experience SAD in the winter, this part of your brain isn't working in the same way.

This could mean your body clock is out of sync with daylight, leading to tiredness and depression. Some researchers think this is because your sleep pattern starts at a different time.

Problems with melatonin and serotonin levels

When it's dark, your brain produces a hormone called melatonin. Melatonin helps your body get ready for sleep. 

Some people with winter SAD seem to produce higher levels of melatonin. 

Levels of serotonin are also affected by how much sunlight you get. Serotonin is a brain chemical that affects your mood.  Some people with SAD seem to have problems regulating serotonin during winter.

Research suggests these can contribute to winter SAD, but the exact relationship between them isn't clear.

The evening is endless. I would watch the clock and feel trapped in the dark.

Weather and temperatures

We all have different experiences of particular seasons and types of weather. You might feel particularly uncomfortable in hotter or colder temperatures. This could contribute to you developing depression at those times. Or it could make any existing depression worse. 

While more people are aware of SAD happening in winter, some people have more difficulty in warmer weather. Some studies have suggested that summer SAD is linked to higher temperatures and humidity. But more research is needed to understand why.

When winter comes and I feel the change in the seasons, I feel more drained. I find it very hard to motivate myself into getting dressed or out of bed.

Do stressful events cause SAD?

Many of us may have times of the year that we find especially difficult. For example, if your work is seasonal, being out of work every winter may contribute to depression. Or you may feel depressed at certain times of the year such as Christmas or bereavement anniversaries.

These feelings aren't necessarily a form of SAD. And you're unlikely to be given a diagnosis of SAD if your depression is linked to a specific situation or event in your life.

But they can still mean that you need extra support at these times of the year.

Our information on seeking help for a mental health problem has tips on how to access support. And our pages on bereavement, stress, and tips for coping at Christmas may also be helpful.

Is SAD more common in certain countries?

SAD is thought to be more common in countries where there are greater changes in the weather and in daylight hours during different seasons. This includes England and Wales.

Are there common misconceptions about SAD?

Lots of people have heard of SAD. But this doesn't mean that they understand what it's like or how you're affected. It doesn't mean you 'just feel a bit low in winter'. There are many factors that can cause SAD or make it worse. It can affect your life just as much as other types of depression.

It can be frustrating and upsetting if people don't understand this. It's important to remember that you're not alone.

Our page on stigma and misconceptions has ideas on how to deal with stigma about mental health.

Sunshine and heat make me feel defensive, misanthropic, angry, anxious, resentful and impatient. I don't want to see anyone, go anywhere or do anything. Even bright, low winter light depresses me. I feel under siege.