Feeling Tired This Winter? Which Blood Tests Are Worth Checking?
Darker days, less time outdoors and changes in routine can make winter feel harder. But persistent tiredness should not automatically be blamed on the season. Blood testing may help investigate anaemia, iron problems, vitamin deficiencies, thyroid dysfunction and other health issues when testing is appropriate.
Not simply because it is winter. However, if you are experiencing persistent fatigue, weakness, feeling unusually cold, reduced exercise tolerance or other unexplained symptoms, targeted blood tests may be useful. The appropriate tests depend on your symptoms, medical history, diet, medicines and individual risk factors.
At Marylebone Diagnostic Centre, the aim is not to test everything. It is to choose a test that answers the right clinical question.
Why can winter feel harder on your body?
There is no single blood test for a “weak immune system”, and winter does not simply switch your immunity off. Instead, several seasonal factors happen at the same time and can affect how you feel.
What changes during a UK winter?
Think of winter as a change in environment and behaviour rather than a simple fall in “immunity”.
During UK autumn and winter, sunlight contains insufficient UVB for most people to make enough vitamin D through the skin.
Colder weather means people spend more time together indoors, creating more opportunities for respiratory infections to spread.
Daylight, sleep, exercise, diet and daily routines can all change during winter and may influence energy and wellbeing.
Winter tiredness can overlap with iron deficiency, anaemia, low vitamin D, vitamin B12 deficiency, thyroid problems and many non-blood-related causes. Symptoms alone cannot tell these apart.
MDC clinical guide: this diagram explains common seasonal factors and is not intended to suggest that everyone becomes immunodeficient during winter.
There is no routine blood test that gives a simple “immunity score”. Tests such as a Full Blood Count can provide useful clinical information, including white blood cell measurements, but they do not measure how “strong” your immune system is.
What might be worth checking if you feel different this winter?
Full Blood Count
An FBC measures red blood cells, haemoglobin, white blood cells and platelets. It can help investigate anaemia and provides useful information when assessing persistent unexplained symptoms.
Iron & Ferritin
Iron deficiency can contribute to tiredness, weakness and reduced exercise tolerance. Iron assessment may be particularly useful when symptoms or medical history suggest deficiency.
Vitamin D
Vitamin D deserves particular attention during the UK winter because sunlight is not sufficient for reliable skin production during the darker months.
Vitamin B12
Vitamin B12 is important for normal red blood cell production and neurological function. Deficiency can contribute to fatigue and weakness.
Thyroid Function
Thyroid disorders can produce symptoms that overlap with winter tiredness, including fatigue, weight changes and increased sensitivity to cold.
Broader Health Markers
If your goal is not simply to investigate tiredness but to understand your overall health, glucose, cholesterol, kidney, liver and other markers may be more appropriately assessed within a structured health screen.
What are you experiencing this winter?
Tap a question below. These guides do not diagnose the cause, but they can help explain which type of testing may be worth considering.
I’m tired all the time. What could I check?
I hardly see daylight. Should I check Vitamin D?
I keep catching colds. Do I need an immunity blood test?
I feel cold and exhausted. Could it be my thyroid?
I’m tired, dizzy or weak. Should I check iron?
I have low energy and brain fog. Should I check B12?
Should I test CRP because I keep getting ill?
I feel perfectly well. Do I need a winter blood test?
Fatigue testing or an overall health check?
These profiles serve different purposes. Choose according to what you actually want to understand rather than simply choosing the largest panel.
Fatigue Profile
A focused blood profile for investigating persistent tiredness or low energy.
- Full Blood Count
- Iron assessment
- Vitamin D
- Vitamin B12
- TSH
- FT4
Best suited to the question: “Why am I feeling tired?”
View Fatigue ProfileMarylebone Health Screening Profile
A broader private health screening profile for people who want a more comprehensive overview rather than investigating fatigue alone.
- Full Blood Count
- Glucose & HbA1c
- Cholesterol
- Kidney function
- Iron & ferritin
- Vitamin D, B12 & folate
- Thyroid markers
- Inflammatory markers
- Additional health markers within the profile
Best suited to the question: “I’d like a broader picture of my health.”
View Health ScreeningIf your concern is specifically fatigue, a focused fatigue profile may be more appropriate. Broader screening is intended for people looking for a wider assessment of their general health.
Does winter testing differ for men and women?
Women experiencing fatigue
Blood count and iron status can be particularly relevant when there is significant menstrual blood loss or other risk factors for iron deficiency. Thyroid, Vitamin D and B12 testing may also be considered according to symptoms and clinical circumstances.
Men experiencing fatigue
FBC, iron status, Vitamin D, B12 and thyroid function may be considered depending on symptoms. Testosterone testing should be symptom-led and appropriately timed rather than automatically included simply because someone feels tired during winter.
Winter health questions
Does your immune system become weaker in winter?
What blood tests can investigate winter fatigue?
Can low Vitamin D make me feel tired?
Can iron deficiency cause tiredness?
Where can I get a fatigue blood test in London?
Should everyone have a large winter health screen?
Persistent or severe fatigue should not automatically be attributed to winter. Seek appropriate medical advice if symptoms are significant, worsening, unexplained or accompanied by concerning symptoms such as chest pain, significant breathlessness, fainting, unexplained weight loss, persistent fever or other acute illness.
Don’t just blame winter. Ask the right health question.
If tiredness or low energy is your main concern, explore the MDC Fatigue Profile. If you want a wider overview of your general health, explore the Marylebone Health Screening Profile.
