Always Feeling Cold (Cold Intolerance): Causes and Tests

Many people have always felt colder than others, often with a family pattern and no other complaints. Such a lifelong, unchanged trait is rarely a reason for concern. The grounds for looking for causes are instead: a new or clearly worsened feeling of cold that appeared in recent weeks or months, cold felt even in a warm room, and above all other symptoms alongside it: tiredness, sleepiness, weight gain or loss, hair loss, dry skin, constipation, pallor, palpitations or dizziness on standing.

It is the set of symptoms, not the feeling of cold itself, that points the way for diagnosis. Cold plus sleepiness, dry skin, constipation and weight gain suggests the thyroid; cold plus pallor, easy tiring and heavy periods, iron; cold plus weight loss and dietary restriction, an energy deficit; cold plus dizziness after standing, low blood pressure. These are only clues, not diagnoses.

Thyroid hormones regulate the rate of metabolism, so a deficiency lowers heat production. Cold intolerance is among the classic symptoms of hypothyroidism, alongside tiredness, lethargy and weight gain, but, as the authors of a review in The Lancet stress, these symptoms are non-specific and the diagnosis is made on biochemical grounds (blood levels of TSH and thyroid hormones), not on the complaints alone.

The conclusion for someone who feels cold: TSH is a reasonable, cheap first-step test, but a normal result largely closes the thyroid thread, and the symptom 'cold' does not justify self-treatment with hormones or 'thyroid' supplements. When the result is abnormal, the doctor decides on interpretation; we write more about this in the entry on hypothyroidism and in the article on hypothyroid symptoms that are easy to mistake for other conditions.

The second best-documented cause is iron deficiency leading to anaemia. Iron is needed to make haemoglobin, and anaemia disturbs both heat production and heat loss: to supply tissues with oxygen the body limits blood flow through the skin, which increases the feeling of cold. A review of this question links poor temperature regulation in people with iron-deficiency anaemia to poorer thyroid function and to the competing oxygen needs of tissues.

Two things in this study matter especially for the reader. First, the effect occurred in women with anaemia, while in those with mere depletion of iron stores (low ferritin without anaemia) the responses were similar to controls, so low ferritin by itself does not prove that it is responsible for the cold. Second, the study was small (30 women) and concerned controlled laboratory exposure, not everyday sensation. A newer, also small study (9 people with mild anaemia and 9 controls) confirmed that in the cold, people with anaemia raised their body temperature more slowly and did not increase heat production, and showed a more pronounced blood pressure response.

The practical conclusion: with a feeling of cold accompanied by pallor, easy tiring, palpitations, hair loss or heavy periods, it is worth testing the blood count and ferritin. We discuss the interpretation of ferritin, including when a low value is an indication for treatment, in the entry on ferritin and the article on low ferritin with a normal blood count; the decision about supplementation and its dose we leave to the doctor.

Fat tissue insulates, and muscles and metabolism produce heat; when body weight is low, or when for a long time one eats decidedly too little relative to expenditure, the body saves energy by lowering the metabolic rate and body temperature. A feeling of cold, bradycardia (slow pulse) and constipation then occur without any thyroid disease in the classic sense. A description of 16 women with anorexia nervosa shows such a picture: during starvation they had cold intolerance, constipation, bradycardia, hypothermia and hypercholesterolaemia together with lowered total T3 and T4, with normal free thyroxine and no rise in TSH.

This is an old, small descriptive study in an extreme clinical situation, so no conclusions about 'ordinary' dieting may be drawn from it. It does, however, show the mechanism: an energy deficit can produce symptoms similar to hypothyroidism without the classic rise in TSH, which distinguishes it from a true thyroid cause. With a feeling of cold combined with dietary restriction, unintended weight loss, menstrual disturbance or intensive training, a medical consultation is advisable, and where an eating disorder is suspected, specialist help. We discuss low energy availability in people who train in the article on excessive tiredness after exercise.

The common impression that women feel cold more often has a physiological basis, but its scale and mechanism are only partly explained. A review of sex differences in thermal sensitivity and perception indicates that differences in body build (lower muscle mass, a different surface-to-mass ratio) account for most, though not all, of the differences in responses to cold.

The practical meaning is that in a woman the mere fact of feeling cold more often is not an alarm. What is worrying is a marked worsening relative to her own norm, especially with other symptoms; and in women an additional, frequent factor is heavy menstrual bleeding leading to iron deficiency, which we write about in the article on heavy periods and anaemia.

Other possible causes include low blood pressure or orthostatic hypotension (a feeling of cold, weakness and dizziness on standing), peripheral circulation disorders and neuropathy (for example in diabetes), vitamin B12 deficiency, some medicines (among others, beta-blockers reduce peripheral blood supply), unrecognised diabetes, and chronic illness and tiredness. Cold fingers that go white and blue in response to cold are associated with Raynaud syndrome; different tests count there than for general feeling cold, as we write separately. The entry on orthostatic hypotension also covers low blood pressure.

In practice few people have one clear cause; more often several small factors overlap: too little sleep, little movement, low muscle mass, irregular meals and a slight iron deficiency. A reasonable work-up therefore does not look for 'one culprit' but checks the set of most common causes that can be measured and treated.

The scope depends on the history; with cold and no other symptoms, TSH and a blood count with ferritin are usually enough. It makes no sense to order yourself a 'full hormone panel', because borderline results can be hard to interpret and cause needless worry.

A feeling of cold is a symptom that is easy to play down and just as easy to over-interpret. If you have always felt cold and nothing else troubles you, it is most likely a personal trait. If it is a change, especially with accompanying symptoms, it is worth checking the thyroid and iron with simple tests and honestly assessing whether you eat and weigh enough. That usually settles the matter or shows whether further work-up is needed, without buying 'thyroid' supplements and without diagnoses from the internet.