Seasonal affective disorder (SAD) is a type of depression that you experience during particular seasons or times of year. Depression is a low mood that lasts for a long time, and affects your everyday life.

If you have SAD, you’ll experience depression during some seasons in particular, or because of certain types of weather or temperature. You can experience it in winter or summer.

What are the symptoms of SAD?

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

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

• Lack of energy
• Difficulty concentrating
• Not wanting to see people
• Feeling sad, low, tearful, guilty or hopeless
• Feeling anxious, angry and agitated
• Being more prone to physical health problems, such as colds, infections or other illnesses
• Sleeping too much, or difficulty waking up (common with SAD in winter)
• Sleeping too little, or waking up a lot (common with SAD in summer)
• Changes in your appetite, for example feeling hungrier or not wanting to eat
• Losing interest in sex or physical contact
• Suicidal feelings
• Other symptoms of depression

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

What causes SAD?

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

• 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 can slow down and gradually stop.
• Disrupted body clock: Your brain sets your body clock by the hours of daylight. 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. 
• Problems with melatonin and serotonin levels: When it’s dark, your brain produces a hormone called melatonin which helps your body get ready for sleep. The levels of serotonin, a brain chemical that affects your mood, are also affected by how much sunlight you get. Some people with winter SAD seem to produce higher levels of melatonin and lower level of serotonin during winter. 
• 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, which could contribute to you developing depression (or any existing depression worsening) at those times.

What treatments are there for SAD?

Using a light box wasn’t perfect but the change was tangible. A real shift. I began to cope better with the dark days and didn’t have the all-encompassing desire to get back into bed and stay there.

• Lifestyle measures: The lack of sunlight is the major factor in causing SAD. The shortage of rays means that we get enough vitamin D, and studies have shown that people with lower levels of vitamin D have a greater chance of developing SAD. Getting as much natural sunlight as possible, exercising regularly and managing your stress levels are key.
• Light therapy: A special lamp called a certified light box is used to simulate exposure to sunlight and has proven to effective for around 85% of diagnosed cases. Without enough morning light your body can fail to produce the hormones to give you energy but a light box can help remedy that. You can buy a light box without a prescription for as little as £25, although you may want to work with a professional to monitor the benefits of the treatment.
• Dawn simulator: This is a device that gradually increases the amount of light in your bedroom in the morning to simulate the rising sun and wake you up. The light gradually increases, just as natural sunlight does, over a period of 30 to 45 minutes. Instead of waking in darkness, you wake to what looks like a sunny morning. This can help reset your circadian rhythm and improve your mood. 
• Medication/supplements: 90% of our essential vitamin D must come from our skin’s exposure to the sun, however during the winter months the sun’s ultraviolet rays are not strong enough for the body to synthesise into vitamin D. Vitamin D supplements are an inexpensive way of effectively combatting SAD. Medication such as selective serotonin reuptake inhibitors (SSRIs) are also sometimes prescribed for SAD although it’s often the last option. 
• Talking therapies: Talking therapies like cognitive behavioural therapy (CBT) or counselling have been found to have positive effects at managing SAD. 

To talk to someone about how you’re feeling today, call our free helpline Guide-Line on 08001 884 884 or talk to us via live chat. If you’re experiencing intense depression and need urgent support, call First Response on 0800 952 1181.