Why Am I So Tired in the Winter? Daylight, SAD and What Helps

The alarm goes off in the dark, the light is fading by mid-afternoon, and by 7 p.m. the sofa feels more persuasive than any invitation. If you have typed why am I so tired in the winter into a search bar, you are not imagining it. Shorter days really do affect sleep, mood and energy, and for some women winter tiredness is part of something worth taking to a doctor. Here is what reputable health sources say, and what can help.

This article is for general information only and isn't medical advice. If you're worried about your symptoms, talk to your doctor.

The Short Answer

Winter tiredness is most often linked to less daylight, which affects the body's sleep-wake rhythm, along with darker mornings, less time outdoors, less movement and the extra demands of the holiday season. For some people, the pattern is stronger and recurs every year; that can be seasonal affective disorder (SAD), a type of depression. Persistent fatigue can also have other medical causes, so if it lasts for weeks, it deserves a check.

1. Less Daylight, a Different Body Clock

The NHS explains that it is not known exactly what causes SAD, but it is thought to be linked to reduced daylight in winter, which may cause changes in brain chemicals such as melatonin and serotonin that affect mood and sleep patterns (the circadian rhythm). Even without SAD, many people notice that dark mornings make waking harder and early dusk makes the evening feel later than it is.

2. Winter Blues vs. Seasonal Affective Disorder

The National Institute of Mental Health (NIMH) notes that many people feel "down" or have the "winter blues" when days get shorter and feel better in spring. SAD is more than that: it is a type of depression with a recurring seasonal pattern, with symptoms lasting about four to five months a year.

Signs that can point to winter-pattern SAD

Alongside the symptoms of depression, NIMH lists these additional symptoms for winter-pattern SAD:

• Oversleeping (hypersomnia)
• Overeating, particularly craving carbohydrates, leading to weight gain
• Social withdrawal, or feeling like "hibernating"

The NHS also lists low mood, losing interest in things you usually enjoy, irritability, difficulty concentrating, and "being more tired and sleeping more than usual." NIMH notes that SAD occurs much more often in women than in men, and is more common in people living farther north, where winter days are shorter. That matters if your life runs between New York, London and Paris.

How it is diagnosed

Only a health professional can diagnose SAD. According to NIMH, the diagnosis requires depressive episodes in a specific season for at least two consecutive years, and the NHS describes a similar two-year pattern. A questionnaire about your moods over time is common.

3. Vitamin D in the Darker Months

The NHS states that between October and early March, people in the UK do not make enough vitamin D from sunlight, and that adults need 10 micrograms of vitamin D a day. UK government advice is that everyone should consider a daily 10-microgram supplement in autumn and winter. The NHS also warns that taking too much over a long period can be harmful, so check with your doctor or pharmacist, especially if you take other medicines or live outside the UK, where advice may differ.

4. Other Causes Worth Ruling Out

Winter is not always the culprit. The NHS page on tiredness and fatigue lists common causes such as poor sleep, stress, depression, hormonal changes (including perimenopause and menopause) and some illnesses, and conditions such as iron deficiency anaemia, diabetes, thyroid problems and sleep apnoea. If your tiredness started before the clocks changed, or comes with other symptoms, it deserves proper attention. Our guides on feeling tired even after sleep and why you're so tired in the afternoon cover other common patterns, and if you are in your 40s, read about perimenopause fatigue.

What May Help (Alongside Your Doctor's Advice)

The NHS self-care advice for SAD and for tiredness overlaps in useful ways:

• Get daylight every day. The NHS suggests getting as much natural daylight as you can and going outside during the day. A morning walk before the office, or lunch outdoors, counts.
• Keep a steady sleep schedule. Going to bed and waking at the same time every day helps, and the NHS suggests aiming for six to nine hours of sleep.
• Move regularly. Regular exercise appears in both NHS pages.
• Stay in contact. Keeping up with friends, family and usual activities is part of the NHS self-care advice, even when hibernating feels easier.
• Protect the evening wind-down. Avoid caffeine, big meals and screens close to bedtime, and keep alcohol moderate during the party season.
• Ask before buying a light box. The NHS says to speak to a GP before trying light therapy, since it may not suit some eye conditions or medicines; if you buy one, 10,000 lux is standard, and it should be UV-free.

When to See a Doctor

• You have felt tired for a few weeks and are not sure why, or it affects your daily life (NHS).
• Your tiredness comes with weight loss, mood changes, or loud snoring and gasping at night.
• Your low mood returns every winter, or treatment is not helping.

If you are struggling or having thoughts of suicide, in the U.S. call or text the 988 Suicide and Crisis Lifeline; in the UK, call 999 in an emergency or contact NHS 111. In life-threatening situations, call your local emergency number.

Frequently Asked Questions

Is it normal to feel more tired in winter?

Feeling somewhat more tired as days shorten is common, and NIMH describes the "winter blues" many people experience. Tiredness that disrupts your life or comes with low mood is worth discussing with a doctor.

Why do I sleep so much in the winter?

Oversleeping is one of the specific symptoms NIMH lists for winter-pattern SAD, and the NHS lists sleeping more than usual among SAD symptoms. Less daylight affects the body clock, but persistent oversleeping should be checked.

Can low vitamin D make you tired?

Vitamin D levels fall in winter because, according to the NHS, the body does not make enough from sunlight between October and early March. Ask your doctor whether a test or supplement makes sense for you, rather than self-prescribing high doses.

Does a SAD lamp work?

The NHS says many people find light therapy helps, though there is not enough evidence for it to be routinely offered on the NHS. Speak to a doctor first.

A Season Planned With Care

Winter does not have to be the season you disappear. Plan fewer, better evenings, protect your mornings and let the light in. For the inner work of presence and self-trust, explore our Presence collection, and browse every Femme Jet Set edition on the guides page.

Health information checked against NHS and NIMH pages on October 26, 2026.