Why You Feel So Tired in Winter, 10 Seasonal Fatigue Causes and Effective Remedies

Why Am I So Tired in Winter? 10 Causes of Seasonal Fatigue

Feeling unusually tired in winter is something many people experience. The mix of cold weather, shorter days, and changes in your routine can make you feel drained, even if you’re sleeping enough. Less sunlight can affect your body clock, lower your vitamin D levels, and change the balance of hormones that control mood and energy. All these factors together can cause what’s known as seasonal fatigue.

When winter begins, you might notice your energy, focus, and motivation drop. You could sleep longer but still wake up feeling tired, crave sugary or starchy foods, or feel heavy and slow during the day. For some, this tiredness is mild and passes on its own, but for others, it can last longer and start to affect daily life.

There are several reasons you might feel more tired in the colder months. These can include low vitamin D, anaemia, thyroid problems, poor sleep, or low mood. Each cause can affect your body in a slightly different way, and discovering the reason for your tiredness is the first step to feeling better.

In this guide, we’ll look at the 10 most common causes of winter fatigue, how to recognise them, and what you can do to boost your energy. We’ll also explain when it might be a good idea to book an online consultation with a clinician, especially if your tiredness keeps coming back or makes it hard to manage your daily routine.

10 Causes of Seasonal Fatigue

There’s not just one reason you might feel extra tired in winter. Cold weather, shorter days, and changes in your routine can all play a part. Here are 10 common causes that can make you feel low on energy during the colder months.

1. Low Sunlight And Circadian Rhythm Drift

In winter, the days are shorter, which means less sunlight in the morning and more darkness in the evening. This can confuse your body clock and make you feel sleepy at the wrong times. When your body produces too much melatonin (the sleep hormone) during the day, it can leave you feeling tired, flat, and less focused, even if you’ve had a whole night’s sleep.

Morning light helps your body clock stay on track. Studies show that getting bright light soon after waking enables you to feel more awake during the day and can even improve your mood. Try to get outside for 20 to 30 minutes of daylight within an hour of waking, especially around breakfast time. If you don’t get much natural light, a special light box can help when used in the morning.

Bright light in the evening has the opposite effect. Too much screen time or intense indoor light before bed can delay your sleep and make you groggy the next day. To sleep better, keep the lights dim in the last two hours before bed and use softer, warmer lamps.

Keeping a regular wake-up time every day, even on weekends, helps your body clock stay steady. If you still feel tired, or if your mood and sleep problems don’t improve, it might be time to book an online consultation with a clinician for extra support.

2. Vitamin D deficiency or low levels

During winter, sunlight is weaker, and people spend more time indoors, so their bodies produce less vitamin D. This vitamin helps control mood, energy, and muscle function. Low levels can make you feel tired, low, or achy. Some studiesshow that people who take vitamin D when their levels are low feel less exhausted after a few weeks, but not everyone sees the same results. This means vitamin D can be part of the problem, but it’s often not the only cause of winter fatigue.

Signs that low vitamin D might be making you tired

You might notice:

• Feeling tired even after resting
• Muscle aches, weakness, or cramps
• Joint or bone pain, especially in the shoulders, hips, or ribs
• Low mood or foggy thinking
• Getting sick more often or taking longer to recover

People with darker skin, older adults, those who are overweight, or anyone who doesn’t get much sun are more likely to have low vitamin D levels.

Vitamin D Levels and What They Mean

25(OH)D Level (nmol/L)	Status	Possible Symptoms	Suggested Action
< 30	Deficient	Fatigue, low mood, muscle weakness	See a clinician, supplement under guidance
30–50	Insufficient	Mild tiredness, reduced energy	Increase dietary sources and sunlight
50–125	Optimal	Normal energy and mood	Maintain a balanced diet and sun exposure
> 125	Excess	Nausea, irritability, high calcium	Stop supplements and seek medical review

What you can do

• Check your levels: Ask your clinician for a blood test called 25-hydroxyvitamin D to see if your levels are low.
• Take supplements if needed: If your levels are below normal, your clinician might suggest vitamin D tablets or drops. Don’t take large doses without advice, as too much can be harmful.
• Support your body in other ways: Vitamin D works best when you also get enough sunlight, eat well, sleep properly, and stay active.
• Follow up: If you start supplements, have your levels rechecked after a couple of months to make sure they’re improving.

3. Seasonal Low Mood, SAD, and Subsyndromal SAD

As the days get shorter, many people notice their mood and energy drop. For some, this becomes stronger and turns into a condition called Seasonal Affective Disorder (SAD) or a milder form known as winter blues. This happens because less daylight affects your body clock, sleep hormones, and the brain chemicals that control mood and energy, such as serotonin.

When this balance is disturbed, you might feel tired, sad, or less motivated. You may crave sugary or starchy foods, sleep more but still feel unrefreshed, and find it harder to concentrate. Even mild winter blues can make you feel low on energy and less interested in your usual activities.

Common signs

• Sleeping longer but still feeling tired
• Strong cravings for sweets or carbs
• Low motivation or poor focus
• Feeling tearful, sad, or irritable
• Losing interest in hobbies or social time
• Persistent tiredness without another clear reason

What can help

• Morning light exposure: Getting bright light in the morning helps lift your mood and reduce Using a special light box for about 30 minutes soon after waking can make a big difference within a week or two.
• Cognitive behavioural therapy (CBT): Talking therapy designed for SAD (called CBT-SAD) helps you change negative thinking patterns and build healthier habits. Research shows it can work as well as light therapy and may last longer.
• Regular physical activity: Exercise boosts energy and mood. Even a brisk 20-minute walk outside can help you feel more alert and positive.
• Stay social and keep a routine: Try to stick to regular sleep and meal times. Plan enjoyable activities and connect with others, even when you don’t feel like it. This helps keep your mood and energy more stable.
• Seek professional support: If your low mood and tiredness don’t improve, book an online consultation. A clinician can check for other causes, such as anaemia, thyroid problems, or vitamin deficiencies, and suggest the proper treatment for you.

4. Anaemia, Iron and B12 Issues

Anaemia happens when your body doesn’t have enough healthy red blood cells to carry oxygen around. Without enough oxygen, your muscles and brain can’t get the energy they need, which makes you feel tired, weak, and light-headed. You might also notice pale skin, shortness of breath, or poor concentration.

Winter can make anaemia worse. Less sunlight means lower vitamin D levels, which can affect how your body uses iron. People also tend to eat fewer iron-rich foods in winter. The most common cause of anaemia is low iron, but low vitamin B12 or folate can cause similar tiredness and weakness. Even mild iron deficiency without full anaemia can make you feel exhausted.

Common signs of anaemia

• Feeling tired or weak most of the time.
• Pale or slightly yellow skin
• Feeling breathless after light activity
• Fast or pounding heartbeat
• Cold hands and feet
• Brittle nails or hair loss
• Feeling dizzy or light-headed
• Sore tongue or mouth ulcers (especially with low B12)

Types of Anaemia and Key Differences

Type	Main Cause	Common Symptoms	Who’s Most at Risk	Typical Treatment
Iron Deficiency	Low iron intake or blood loss	Fatigue, pale skin, cold hands, dizziness	Menstruating women, vegetarians	Iron supplements (after testing), diet changes
Vitamin B12 Deficiency	Poor absorption or low intake	Numbness, memory problems, fatigue	Older adults, vegans	B12 injections or oral supplements
Folate Deficiency	Low folate intake	Fatigue, mouth ulcers, poor appetite	People with a poor diet or high alcohol intake	Folate supplements, leafy greens, fortified foods

Possible causes and risk factors

• Heavy periods
• Low iron intake (for example, vegan or vegetarian diets without supplements)
• Stomach or bowel problems like coeliac disease
• Long-term illness or inflammation
• Low B12 levels, often linked to ageing or absorption problems
• Some medicines that affect stomach acid or vitamin absorption

What you can do

• Ask for a blood test: Your clinician can check your red blood cell count, ferritin (iron stores), vitamin B12, and folate levels. This helps find out what’s causing your tiredness.
• Don’t take iron on your own: Taking iron tablets without testing first can cause side effects or hide other problems. Always follow a clinician’s advice.
• Eat foods rich in iron and B12:
  • Iron: lean red meat, chicken, fish, beans, lentils, tofu, and spinach.
  • B12: eggs, dairy, fortified cereals, or supplements if you don’t eat animal products.
  • Have vitamin C foods (like oranges or peppers) with iron-rich meals to help your body absorb more iron.
• Treat the cause: If you’re diagnosed with a deficiency, your clinician might check for things like blood loss or poor nutrient absorption.
• Support your recovery: Getting your iron or B12 levels back to normal can take a few weeks. Good sleep, regular gentle exercise, and staying hydrated will help your energy improve.

If your tiredness doesn’t get better after treating anaemia, or if you’re unsure what’s causing it, book an online consultation to get more personalised advice.

5. Thyroid changes and slow metabolism

Your thyroid is a small gland in your neck that controls how your body uses energy. It makes hormones that help with body temperature, mood, and metabolism (how your body turns food into energy). If your thyroid is underactive (called hypothyroidism), everything slows down, and you may feel tired, cold, or low in mood.

Winter can make these symptoms more noticeable because your body naturally slows down a bit in the cold. Thyroid problems are more common in women, especially after age 40, but anyone can have them.

Common signs of a slow thyroid

• Feeling tired all the time
• Feeling cold even in warm places
• Gaining weight or finding it hard to lose weight
• Dry skin or hair loss
• Constipation
• Slow thinking or forgetfulness
• Feeling sad or low in mood

Possible causes and risk factors

• Autoimmune thyroid disease (like Hashimoto’s)
• Family history of thyroid problems
• Low iodine levels (rare in the UK but still possible)
• Some medicines that affect thyroid hormones

What you can do

• Ask for a thyroid test: Your clinician can do a simple blood test to check if your thyroid is working correctly.
• Follow your treatment plan: If you have low thyroid levels, medicine such as levothyroxine can replace the missing hormones and help you feel more energetic again.
• Support your thyroid naturally:
  • Eat a balanced diet with enough protein, iron, and selenium (found in eggs, fish, and nuts).
  • Get regular sleep and gentle exercise to boost your energy.
  • Try not to skip meals, as this can make tiredness worse.
• Give it time: It may take a few weeks for your energy and mood to improve after treatment starts.

6. Poor winter sleep habits

Many people think they sleep more in winter, but sleeping longer does not always mean sleeping better. Shorter days and longer nights can confuse your body clock, making it harder to fall asleep or stay asleep. Cold weather can also lead to staying in bed longer, eating heavier meals, and spending more time on screens before bed, all of which affect deep, refreshing sleep.

Studies show that people often spend more time in bed during winter but sleep less efficiently. They may wake up more often or take longer to fall asleep. Less sunlight during the day also delays your body’s sleep hormones, making you feel tired in the morning and wide awake at night. This mismatch is sometimes called “social jetlag,” when your sleep schedule and body clock do not match.

Signs your sleep habits might be causing tiredness

• Waking up groggy even after a whole night’s sleep
• Trouble falling asleep or waking up often
• Feeling extra tired on weekends or after long lie-ins
• Needing naps makes it harder to sleep later
• Relying on caffeine to stay awake
• Feeling moody, foggy, or irritable during the day

Poor Winter Sleep Hygiene

Good Sleep Habits	Habits That Disrupt Sleep
Fixed wake and bedtime	Irregular sleep schedule
Morning daylight exposure	Late-night screen time
Cool, dark bedroom (17–19°C)	Overheated or noisy room
No caffeine after 2 p.m.	Evening caffeine or alcohol
Gentle wind-down routine	Working or scrolling in bed

How to sleep better in winter

• Get morning light: Go outside within an hour of waking, even on cloudy days. Morning daylight helps reset your body clock and makes you feel more alert.
• Stick to a routine: Try to go to bed and wake up at the same time every day, including weekends. This helps your body know when it is time to sleep.
• Keep your bedroom cool and dark: A temperature between 17°C and 19°C is best for deep sleep. Use light, breathable bedding and block out light where possible.
• Avoid screens before bed: Blue light from phones and TVs can stop your brain from producing melatonin, the sleep hormone. Dim the lights and put away screens an hour before bedtime.
• Watch your evening habits:
  • Avoid caffeine after mid-afternoon.
  • Limit alcohol, as it can disturb deep sleep.
  • Eat lighter dinners at least two hours before bed.
• Wind down before sleep: Gentle stretches, reading, or mindfulness can help your body relax and prepare for rest.

7. Physical inactivity and loss of fitness

When it gets cold and dark, most people move less. You might stay indoors more, sit longer, or skip regular exercise. But when you move less, your body slows down. Your muscles get weaker, your blood flow drops, and your energy levels fall. This creates a cycle where feeling tired makes you move less, and driving less makes you even more tired.

Studies show that just two weeks of increased sitting can make your muscles less efficient and increase tiredness, especially in people who are generally active. In winter, people often take 30 to 40 percent fewer steps than in summer, which adds to fatigue. Less sunlight also means lower serotonin, a brain chemical that helps you feel motivated and upbeat.

Simple ways to stay active this winter

• Break up sitting time: Stand up or walk for a few minutes every half hour. Even small breaks improve blood flow and help you feel more awake.
• Add small movements (NEAT): Try walking while on calls, doing light housework, or stretching. These small movements add up and keep your body active.
• Do short workouts: If long workouts feel hard, try 10-minute sessions of squats, lunges, or climbing stairs. Short bursts of movement can still boost energy.
• Get outside when you can: A brisk 20-minute walk in daylight provides both exercise and natural light, which helps improve mood and sleep.

8. Winter infections and post-viral tiredness

Winter is a standard time for colds, flu, and other viral infections. Even after the main symptoms go away, you might still feel tired for weeks. This is called post-viral fatigue. Your body uses a lot of energy to fight infection and then needs time to repair and recover. If this recovery is rushed or incomplete, you can be left feeling exhausted, foggy, and low on energy.

Studies show that after some infections, the immune system can remain active for a while, affecting how your body produces energy. People who try to get back to full activity too soon often take longer to recover. Resting well and returning to normal slowly helps your body heal faster.

Common signs of post-viral fatigue

• Ongoing tiredness, even after resting or sleeping
• Muscle or joint aches
• Brain fog or poor concentration
• Unrefreshing sleep
• Low mood or irritability
• Feeling worse after physical effort

How to recover and regain energy

• Rest, but keep moving gently, as complete bed rest can make you weaker. Try gentle movement such as stretching or short walks. Start small and build up slowly.
• Prioritise good sleep: Illness can upset your sleep routine. Go to bed and wake up at the same time each day, keep evenings calm, and get daylight in the morning.
• Eat to help recovery:
  • Include protein foods like chicken, fish, eggs, or tofu to repair tissues.
  • Eat anti-inflammatory foods such as berries, olive oil, nuts, and green vegetables.
  • Drink plenty of fluids, about 6 to 8 cups of water or warm drinks each day.
• Pace yourself: Avoid doing too much on days you feel better. Stop and rest before you get exhausted, then slowly increase activity as your energy improves.
• Manage stress and mood: Feeling frustrated or low is normal when recovery takes time. Mindfulness, breathing exercises, or calm activities can help your body relax and heal.
• Track your progress: Keep a simple diary of your sleep, energy levels, and activity. This helps you notice patterns and share helpful information with your clinician.

9. Dehydration and poor winter nutrition

In cold weather, most people drink less water without realising it. You may not feel as thirsty, but your body still needs fluids to stay healthy. Even mild dehydration can make you feel tired, dizzy, or find it harder to concentrate. At the same time, winter eating habits often change, and people tend to eat heavier comfort foods and fewer fruits and vegetables. This can lead to low levels of essential nutrients your body needs for energy, focus, and mood.

When you do not drink enough water or eat a balanced diet, your blood flow slows down, your muscles feel weaker, and your energy drops. A poor diet can also cause your blood sugar to rise and fall quickly, leading to energy crashes and tiredness.

How dehydration and poor diet cause winter tiredness

• Thicker blood flow makes your heart work harder.
• Electrolyte loss affects your nerves and muscles.
• Low nutrients such as iron, B vitamins, and magnesium can lead to weakness and low mood.
• Crashes from sugar in processed foods lead to sudden drops in energy.
• Weaker immunity makes you more likely to get sick and feel run-down.

Simple ways to stay hydrated and eat better in winter

• Drink enough fluids: Aim for 6 to 8 cups of water or warm drinks each day. Herbal teas and soups also count. Try warm lemon water if plain water feels too cold.
• Eat hydrating foods: Soups, stews, oranges, and other citrus fruits help add extra fluids.
• Limit caffeine and alcohol: Too much can dehydrate you and disturb sleep. Have a glass of water between drinks.
• Balance your meals:
  • Include lean protein such as chicken, fish, eggs, tofu, or beans.
  • Add iron-rich foods such as lentils, spinach, or red meat, and pair them with vitamin C foods like tomatoes or peppers to help absorb the iron.
  • Choose slow-release carbohydrates such as oats, brown rice, or root vegetables for steady energy.
• Boost mood and immunity:
  • Eat foods with omega-3 fats, for example, salmon, mackerel, flaxseed, and walnuts.
  • Get enough B vitamins and magnesium to support energy and reduce stress.
  • Include vitamin C and zinc to help your immune system.
• Plan: Prepare simple, healthy meals in batches, such as vegetable soups, lentil stews, or overnight oats with berries. This makes it easier to avoid processed snacks.

10. Stress, overwork, and holiday burnout

Winter tiredness is not just about cold weather and short days. Stress, long work hours, and busy holiday schedules can also leave you feeling exhausted. End-of-year deadlines, money worries, and social pressure can build up, making you feel drained before the holidays even start. Ongoing stress affects your hormones, sleep, and immune system, which can lead to low energy and poor focus.

Shorter days and less sunlight can worsen stress by lowering serotonin and vitamin D levels, which affect mood. When you add work pressure, family demands, and poor sleep, your body and mind can both start to feel overloaded.

Signs you may have stress-related tiredness

• Feeling mentally or emotionally exhausted even after resting
• Struggling to focus or make decisions
• Muscle tension, headaches, or clenching your jaw
• Feeling irritable, frustrated, or low in mood
• Relying on caffeine or sugar to stay alert
• Sleep that feels light or unrefreshing
• Enjoying things less than usual

Simple ways to manage stress and prevent burnout

• Notice your stress triggers: Spend a few minutes each evening thinking about what feels most tiring, such as work, finances, or lack of sleep. Once you know the cause, you can take steps to reduce it.
• Set clear boundaries: Try to finish work at the same time each day and avoid checking emails after hours. Switching off properly helps your brain recover and improves next-day energy.
• Take short breaks: Stand up, stretch, or take a few deep breaths every hour or so. Even quick breaks can reduce stress and boost focus.
• Practise relaxation:
  • Try box breathing (breathe in for 4 seconds, hold for 4, breathe out for 4, hold for 4).
  • Gently tense and relax your muscles one group at a time.
  • Go for a short walk or write in a journal to calm your mind.
  • Short mindfulness sessions like these can lift energy and reduce stress.
• Balance social time and rest: It is easy to feel pressured to attend every holiday event, but too much social activity can be tiring. Choose gatherings that make you feel good and skip the ones that drain you.
• Keep a steady routine: Regular sleep, meals, and light exercise help your body manage stress and keep your energy stable.

Stress can sneak up slowly during winter. Paying attention to your limits, making time to relax, and keeping healthy routines can stop tiredness from turning into complete burnout.

Conclusion

Feeling tired in winter is very common. Shorter days, colder weather, and less sunlight can all make your body and mind feel low on energy. Things like low vitamin D, poor sleep, stress, or even mild illness can build up and leave you feeling worn out.

The good news is that you can turn this around with small, steady changes. Getting more daylight, eating balanced meals, moving a bit every day, drinking enough water, and keeping a regular sleep routine all help boost energy and mood.

If you still feel tired even after making these changes, it’s a good idea to talk to a clinician. Mobi Doctor can help you check for causes such as vitamin D deficiency, anaemia, or thyroid problems through an online consultation. Our doctors offer safe, expert advice and practical next steps to help you feel like yourself again.

Winter tiredness doesn’t have to control your days. With a few healthy habits and the right help, you can feel brighter, stronger, and ready to enjoy the season.