Always feeling cold: what your thyroid and iron have to do with it

Always feeling cold usually comes from a mix of build and metabolism: little muscle mass, a low weight, and sometimes a thyroid working more slowly or low iron stores. Whether it's worth measuring depends mostly on one question: is it new?

If you've been the cold one your whole life, it probably just belongs to you. If it changed over recent months, that's a different conversation.

Why are you always cold?

You make heat mainly in your muscles and organs, and lose it through your skin. Anyone with little muscle mass makes less heat. Anyone slim loses it faster, because there's relatively a lot of skin surface against not much mass.

On top of that, your thyroid helps set the pace of that heat production. When it runs slower, your basal metabolic rate drops and you notice it in your hands and feet.

In women, skin blood flow also responds more strongly to temperature changes. That explains part of the office thermostat argument.

Your thyroid sets your heat production

Feeling cold is one of the classic complaints in an underactive thyroid. Usually more comes with it: fatigue, dry skin, slower thinking, and sometimes weight gain without eating differently. It's that combination that makes the story specific, not the cold alone.

A 2024 Lancet review describes the symptoms of hypothyroidism as broad and not very specific. That's exactly why people carry it for a long time without thinking of it.

The values that offer insight are TSH and free T4. More on that in thyroid symptoms, values and which blood test gives insight.

Iron: less oxygen, less heat

Iron sits inside haemoglobin, which carries oxygen to your tissues. With low iron stores your muscles and skin get less oxygen, and that translates into feeling cold and tired. Ferritin reflects those stores.

The trap is that ferritin can already be low while your haemoglobin still reads normal. Clinical Medicine called iron deficiency without anaemia a diagnosis that matters in 2021, and a 2025 JAMA review describes it in adults as frequently missed.

Low stores are more common in women who menstruate, in athletes, and in people who eat little meat.

When does it belong to your build?

When it has always been this way, when both hands and feet are equal, when they warm up indoors, and when nothing else has joined in. Then there's usually no measurable cause, and that's a perfectly good outcome too.

RIVM, the Dutch national institute for public health, tracks how often nutrient shortfalls occur in the Netherlands, and for most people eating a varied diet those aren't the explanation.

Why women feel cold more often

Three things run at once. Women have less muscle mass on average, their skin blood flow responds more strongly to temperature changes, and in anyone who menstruates the iron stores sit low more often. Those three together explain most of the difference.

So it's rarely one cause. It's a sum that just tips over a threshold.

That also makes the office thermostat argument genuine: at the same room temperature, two people really do feel something different. There's no winner in that conversation.

What does change is the meaning when it's new. A woman who has always been cold and a woman who has been cold since this spring don't have the same story.

When does it become worth measuring?

When something else has joined in. Cold plus fatigue, cold plus thinning hair, cold plus breathlessness on stairs: those are the combinations that make a measurable cause more likely than simply being a cold person.

A concrete example. You're 41, you were never cold before, and for about four months you've been putting on a cardigan indoors while your colleagues sit in short sleeves. On top of that you're falling over at nine in the evening. That's exactly the pattern where your thyroid and your iron stores become worth looking at.

Imagine two results come back: a TSH of 6.4 mU/l and a ferritin of 13 µg/l. Two values both pointing towards the same feeling, by two different routes.

What I find interesting about this is that neither one is the whole story on its own. They reinforce each other, and that's precisely why cold and tiredness turn up together so often. Your GP looks at the combination, not at a single number.

What you can do next

If your story fits the pattern that's new, your thyroid and your iron stores are the logical first step. A TSH test or a ferritin test can be done without a referral, and you discuss the result with your GP afterwards.

Don't start with everything at once. Take the value that fits what else you notice.

The full list of causes is in cold hands and feet: 8 causes. If it's mainly your feet, read always cold feet.

Sources

• Hypothyroidism. The Lancet, 2024. PMID 39368843
• Iron deficiency without anaemia: a diagnosis that matters. Clinical Medicine (London), 2021. PMID 33762368
• Iron Deficiency in Adults: A Review. JAMA, 2025. PMID 40159291
• Iron deficiency anaemia. The Lancet, 2016. PMID 26314490

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.