Always Cold? The Blood Tests That Explain Why

1. Why do I feel cold all the time?

Your body holds a steady core temperature. Doing that takes fuel, oxygen and a working thermostat. When one of those runs short, you feel it as cold. These are the usual reasons:

• An underactive thyroid.The NHS lists “feeling cold more than usual” as a symptom. A slow thyroid turns your metabolism down, so you make less heat.
• Low iron. Too few healthy red cells means less oxygen reaching your hands and feet.
• Low vitamin B12. B12 is needed to build red blood cells, and low levels can also cause pins and needles.
• Very little body fat. Fat insulates. Hard dieting or a low body weight both make you feel the cold quickly.
• Raynaud’s phenomenon. A common circulation quirk that turns fingers and toes white or blue in the cold.
• Poor sleep and a hard training block. Both leave you run down, and feeling cold often comes with it.

“Symptoms usually develop slowly and get worse over time.”

— NHS, Underactive thyroid (hypothyroidism)

That slow build is the catch. You rarely notice the day you started feeling the cold. You just look up a year later and realise the heating is always on.

2. When is feeling cold worth testing?

Some people simply run cold, and always have. That is not a problem to solve. What matters is a change, and what travels with it.

It is worth looking closer if the cold is new, or if it arrives with other signs:

• Deep tiredness that sleep does not fix, covered in our always tired guide.
• Weight gain with no change to how you eat.
• Dry skin, thinning hair, or heavier periods.
• Breathlessness, palpitations, or unusually pale skin.
• Brain fog, low mood, or pins and needles in your hands.

Cold fingers that change colour are a separate story. The NHS describes Raynaud’s as “where your blood stops flowing properly to your fingers and toes”. It is usually harmless. See a GP if it is severe, if it is getting worse, or if it starts for the first time after 30.

None of these symptoms names its own cause. A slow thyroid, low iron and low B12 all feel much the same from the inside. That is the argument for a number rather than a guess.

3. Which blood markers explain feeling cold?

Four markers do most of the work here. Each one maps to a different cause on the list above.

• TSH. The signal your brain sends to the thyroid. A high TSH is the first clue the gland is running slow. Our TSH guide covers the UK range.
• Free T4. The main hormone the thyroid makes. Read it with TSH, never alone.
• Vitamin B12. Low B12 is common, easy to miss, and shows up as tiredness and tingling. See our B12 guide.
• Vitamin D. Low levels are very common in UK winters and track with the same flat, run-down feeling.

Iron is the honest gap. Ferritin and a full blood count are not in Helvy’s current finger-prick panels, so your GP is the right route for those. Our iron deficiency guide explains what to ask for.

TSH, free T4, B12 and vitamin D all sit in Helvy’s General Energy & Wellness panel (£149). The Thyroid & Vital Organs panel (£159) adds free T3 and kidney and liver markers. Both are home finger-prick tests, with results in about five working days from UKAS-accredited UK laboratories.

4. What should I do next?

Start by writing down what else changed. Energy, weight, mood, skin, periods, sleep. That list is worth more than the cold on its own, both to you and to a clinician.

Then get the markers read. If a thyroid result comes back outside the range, take it to your GP. A test measures biomarkers and gives you wellness insight. It does not diagnose a thyroid condition, and it is not a substitute for seeing someone.

If everything reads normal, that is useful too. It moves the question on to sleep, training load, body fat and stress, which our normal results but still feel ill guide picks up. You can browse every thyroid guide in the thyroid hub.

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