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Understanding Seasonal Affective Disorder
- Dr Joseph Nightingale
- 4 hours ago
- 6 min read
Why Winter Affects Your Mood
When the nights get darker, it’s common to find your mood lowering. While most of us experience normal mood fluctuations throughout the year, sometimes a low mood coincides with seasonal changes in weather or temperature.
This is known as seasonal affective disorder, a type of depression linked to reduced sunlight exposure and changes in our internal body clock.
And it’s not just mood that feels the impact. The same lack of sunlight, cold temperatures, and time spent indoors can also influence your energy levels, immune system, and overall wellbeing. Supporting your vitamin D levels, eating well, and checking your health through simple blood tests can all make a difference.
See our guide for more everyday tips: Christmas Health Hacks: Simple Tips for Enjoying the Holidays.
What is Seasonal Affective Disorder (SAD)?
Seasonal affective disorder (SAD) is a type of depression that occurs during the autumn or winter months. Depression is characterised by low mood, low energy, and loss of interest in things you normally enjoy.
Other names for SAD include winter blues, winter depression, or seasonal depression.
Depression can occur anytime, but SAD is specifically triggered by changes in daylight, weather, or temperature, though some people experience it in summer, too. Low vitamin D levels are thought to contribute to SAD symptoms. Around 40% of people aged 19-64 years are vitamin D deficient during the winter months.
Get your vitamin D levels checked with Health KIinix to see if you have a deficiency.
When Does Seasonal Affective Disorder Start?
In most cases, SAD begins in the late autumn or early winter, as daylight hours shrink and temperatures drop. More specifically, in the UK, symptoms can start in late October and are most severe during December, January, and February.
The average duration of the winter pattern is about 4-5 months.
It’s estimated that around 1 in 15 people (~7%) experience some form of SAD in a given year. The vast majority follow the winter pattern; however, some people undergo the “summer pattern,” beginning in spring/early summer.
Can You Get SAD in the Summer?
Yes, SAD can occur in summer.
Also known as “reverse SAD,” the symptoms are also the opposite of traditional winter depression. People may notice trouble sleeping, poor appetite, weight loss, agitation or anxiety, and increased irritability.
The condition is likely caused by longer days, higher temperatures, humidity, and changes in routine. Bright light, especially during the evenings, can disrupt your circadian rhythm and delay sleep onset. Plus, the pressure to “enjoy” summer or stress related to body image can further lower your mood.
Who Can Experience SAD?
Anyone can experience SAD.
Often, it occurs in people with a pre-existing background of depression. The further low light, short days, and cold temperature exacerbate the underlying low mood, causing SAD to occur.
SAD is also worsened by a lack of vitamin D. People who work inside — such as office workers, healthcare professionals, or people in the service industry — may not experience any daylight during the winter months. Low vitamin D levels contribute to depression.
Cold, grey days can make us more vulnerable. If you’re unemployed or work is seasonal, suffer a bereavement, or experience some other stressor, it can tip us over the edge. Where in summer, a warm, sunny day can cheer us up, in winter, a grey, cold day can push us down.
Symptoms of Seasonal Affective Disorder
Seasonal affective disorder can look and feel much like other forms of depression, but it tends to follow a clear seasonal pattern. Common symptoms include:
Persistent low mood or sadness that lasts most of the day, nearly every day
Loss of interest or pleasure in activities you usually enjoy
Low energy or constant fatigue
Sleeping more than usual or struggling to get out of bed
Increased appetite, especially cravings for carbohydrates, often leading to weight gain
Difficulty focusing or making decisions
Feelings of hopelessness, worthlessness, or guilt
In severe cases, thoughts of not wanting to live
In contrast to spring and summer SAD, autumn and winter SAD often manifests as oversleeping, increased appetite (especially cravings for high-carbohydrate foods), weight gain, and tiredness or low energy.
When to Speak to a Doctor
Most people who experience SAD may not even realise. They struggle through the season trying to keep going through festive events, seeing friends and family, or making their environment warmer and more comfortable.
But that’s not the case for everyone.
The NHS recommends seeking help for SAD-related depression if you’re struggling to cope. That could be oversleeping, struggling to work, neglecting self-care, or cancelling social events. It’s easy to spiral without an outside perspective.
Charities like MIND also offer helpful resources. See their guide on seasonal affective disorder for further information. If you ever experience thoughts of self-harm, seek immediate help by contacting NHS 111 or Samaritans on 116 123.
How to Help Someone with Seasonal Affective Disorder
Noticed a friend, family member, or colleague is experiencing SAD? You can make a difference. The biggest issue is raising the issue. Most people might not even realise their mood is lowering in the winter. It can become such a pattern in their life that they think it’s normal.
Gently broach the subject: “I’ve noticed you seem a little quieter recently,” or “You’re not quite yourself when it gets darker outside.”
If they’re happy to talk about it, you can suggest some ideas. Going for a walk during lunch, spending time with loved ones, or enjoying seasonal activities can all help lift their mood.
How to Treat Seasonal Affective Disorder
While there’s no single cure for SAD, a combination of lifestyle changes, light exposure, and professional support can make a significant difference. The right approach depends on how severe your symptoms are and how much they affect your daily life.
SAD Lamps
Light therapy can help reset your body clock and improve your mood. Using a SAD lamp for around 30 minutes each morning may ease symptoms. Check with your GP before starting, especially if you have eye conditions or take photosensitising medication.
Talking Therapies
Cognitive behavioural therapy (CBT) and similar approaches can help you manage negative thoughts and develop coping strategies for the winter months.
Antidepressants
Your GP may recommend antidepressants such as SSRIs if symptoms are more severe or persistent.
Lifestyle Changes
Getting outside during daylight, exercising regularly, and maintaining a healthy diet all help support mood. Try to cut back on alcohol, which can worsen low mood and sleep issues.
Read more in How Does Dry January Affect Your Body.
Can Vitamin D Help with Seasonal Affective Disorder?
Almost everyone should take a vitamin D supplement during the winter months (especially those with darker skin tones).
The NHS recommends everyone in the UK to consider a daily 10-µg vitamin D supplement from late September to early April.
You should aim to get 15-30 minutes of sunlight per day (if possible). Vitamin D is also found in several foods, including oily fish, red meat, egg yolks, and fortified foods (some cereals and fat spreads). This can further help support your levels.
How to Prevent SAD
If you know you’re vulnerable to SAD, try to build in preventative measures. These can make a real difference.
One of the biggest is getting some daily sunlight exposure. Even sitting near a bright window can help lift your mood and mimic natural sunlight. If that’s not possible, going for a brief walk during your lunch break (even for just 15 minutes) will make a difference. Trying to get some sunlight early in the morning can also help your circadian rhythm, leading to better sleep.
Don’t just sit with your low mood. Connecting with friends, attending local social events, and trying to speak to at least one person a day can combat loneliness. While it can feel difficult when your mood is low, the hardest part is getting started. Once you’re there, it gets a lot easier.
Lastly, alter your environment. Making your space light and decorating with nice things makes a huge difference. There’s nothing worse than sitting in a dark room.
If you struggle with low mood during the darker months, remember that help is available. Speak to your GP or a qualified therapist if symptoms persist. You can also support your overall wellbeing year-round by checking in on your key health markers. Book a Well Woman Check to stay on top of your energy, hormones, and nutrient levels.
References
Mayo Clinic | Seasonal Affective Disorder (SAD)
Nuffield Health | Seasonal Affective Disorder: The Signs, Symptoms, and Treatments
Written by:
Dr Joseph Nightingale, MBBS, MSc
Approved by:
Consultant Physician in General Internal Medicine
MBBS, MRCP(UK), DTM&H, MRCGP, DCH, DRCOG, DFFP