Feeling tired in winter is common. Dark mornings, colder weather and busy schedules all take their toll. But tiredness that lingers for weeks, or that sleep does not seem to fix, is a symptom worth taking seriously, not a personality trait you simply have to live with. At The Wright Practice, we explain the medical causes of persistent fatigue, which warning signs matter, and how a proper assessment finds the cause rather than guessing.
A few quick answers before we go into more detail.
Fatigue is a symptom rather than a diagnosis, and it has many possible causes. The table below sets out the most common ones, what else you might notice, and how each is usually checked.
| Possible cause | Other clues you may notice | How it is usually checked |
|---|---|---|
Iron deficiency or anaemia | Breathlessness on exertion, pale skin, heavy periods, feeling cold | Full blood count and ferritin (iron stores |
Underactive thyroid | Weight gain, feeling cold, dry skin, low mood | Thyroid function blood test (TSH, often free T4) |
Low vitamin B12, folate or vitamin D | Aching muscles, pins and needles, sore tongue, low mood | Specific vitamin blood tests |
Type 2 diabetes or raised blood sugar | Thirst, passing urine more often, weight change | HbA1c (average blood sugar over about three months) |
Sleep apnoea | Loud snoring, gasping at night, unrefreshing sleep, daytime sleepiness | Clinical assessment, then a sleep study if needed |
Low mood, anxiety or burnout | Poor sleep, loss of interest, feeling overwhelmed | Clinical conversation and screening questions |
Some tiredness in winter is expected. Shorter days affect sleep and mood, and many of us move less and see less daylight. This kind of tiredness usually eases with a few better nights, some fresh air or a quieter week.
Fatigue that is worth investigating looks different. It lasts for several weeks, it does not improve with rest, or it gets in the way of work, relationships or the things you enjoy. Many people spend years assuming this is normal for them, which is why so many only seek help when it becomes hard to ignore.
Most persistent fatigue is not caused by anything dangerous. Some symptoms alongside it, however, deserve prompt medical attention rather than waiting to see if things settle.
If you have any of these, contact a doctor soon. If you are in crisis or feel unsafe, call 999 or NHS 111.
Reaching for a supplement is understandable, but it can mean months of guesswork. If your tiredness is caused by an underactive thyroid or sleep apnoea, no vitamin will fix it. If you are iron deficient, taking iron without a test can delay finding out why your levels are low.
A targeted assessment works the other way round. It starts with your history, looks for patterns, and uses selected tests to confirm or rule out likely causes. For nutrition and energy tips alongside this, our blog on the fatigue-fighting diet is a useful companion.
There is no single test for tiredness. Which tests make sense depends on your symptoms and history, but a first set commonly includes the following.
These can be arranged through our private blood testing and biomarker assessment service, so your results are reviewed together by a doctor rather than one number at a time.
If your fatigue may be hormone-related, our perimenopause and menopause service and men’s health assessments look at this in more detail.
Your appointment starts with a conversation. Your doctor will ask when the tiredness began, how it varies through the day, how you sleep, what you eat and drink, what medicines you take, and what else is going on in your life. They will usually examine you and check your blood pressure.
From there, you will agree which tests are worth doing. If results are normal, that is useful information too, and the focus shifts to sleep, stress, mood and lifestyle. If something is found, you will leave with a clear next step, whether that is treatment, monitoring or referral to a specialist.
“Patients often tell me they have been tired for years and assumed it was just life,” says Dr Dan Wright. “Sometimes it is, but sometimes there is a treatable cause sitting behind it. We take the time to listen first, test thoughtfully, and explain what each result does and does not mean, so you are not left guessing.”
This approach runs across every consultation at our 101 Harley Street clinic, including our private GP services and Wellperson health assessments.
The NHS advises seeing a GP if you have been tired for a few weeks and are not sure why, or if it affects your daily life. Do not wait if you also have other symptoms such as weight loss, fevers or breathlessness.
Yes. Iron deficiency is one of the most common treatable causes of tiredness, particularly in women with heavy periods. A full blood count and ferritin test can show whether your iron stores are low.
Yes. An underactive thyroid slows many body processes and commonly causes tiredness, weight gain, feeling cold and low mood. A thyroid function blood test can check for it.
It can be. Low B12 or folate can cause anaemia and tiredness, sometimes with pins and needles or a sore tongue. People who eat little animal food, take certain medicines or have digestive conditions are more at risk.
It could be if you snore loudly, gasp or choke at night, or wake unrefreshed despite enough hours in bed. Sleep apnoea is assessed clinically and, if suspected, confirmed with a sleep study.
Yes, and they are very common causes. Poor sleep, anxiety and low mood all drain energy. A good assessment at The Wright Practice looks at these alongside blood tests rather than assuming everything is physical.
A normal result is reassuring and still useful. It narrows down the possibilities, and the focus can shift to sleep, stress, mood, diet and activity. Your doctor will explain what the results do and do not rule out.
It is possible, but ME/CFS is only considered after other causes have been looked for, and symptoms usually need to have lasted about three months. If your tiredness is severe and worsens after activity, mention this to your doctor.
Not always. Low vitamin D can contribute to tiredness, but many other causes are more common. A doctor at The Wright Practice can help you decide whether it belongs in your tests.
Tiredness that will not shift deserves a proper answer, not more guesswork. Book a consultation with The Wright Practice today to find out what is behind it.
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