Why Am I Always Cold? What Your Thyroid Is Telling You

You wear a sweater when everyone else is in short sleeves. Your hands and feet are cold even in bed. If you are always cold, your body is telling you it is not making enough heat, and your thyroid is the first place to look.

The short answer

Your body heat comes from your metabolism. Your thyroid sets the pace of that metabolism, and iron carries the oxygen your cells burn to make heat. When your thyroid runs slow, your iron is low, or both, you make less heat and you feel cold. Blood sugar swings, low calorie intake and long-term stress can add to it. You can test for each of these, so you do not have to guess.

How your thyroid controls your body heat

Your thyroid makes T4, which your body converts into T3, the active form. T3 tells almost every cell in your body how fast to burn fuel. Burning fuel makes heat. When T3 is low, your cells slow down, and you produce less heat.

Researchers have described thyroid hormone as one of the main regulators of how your body makes heat (Silva, Physiological Reviews, 2006). That is why feeling cold is one of the most common signs of low thyroid function.

Being cold rarely shows up alone. Look for these signs together:

• Cold hands and feet, even in a warm room
• Tiredness that sleep does not help
• Dry skin and brittle nails
• Hair thinning or falling out, including the outer third of your eyebrows
• Constipation
• Weight that will not move even when you eat well
• A slow pulse or a low morning temperature

If several of these sound like you, read what hair loss says about your thyroid.

Why your labs can look normal when you are still cold

Most people only get a TSH test. TSH is a signal from your brain to your thyroid. It does not show how much active T3 is reaching your cells.

You can have a normal TSH and still be low in free T3. You can also be making too much reverse T3, an inactive form your body makes under stress, illness or calorie restriction. Reverse T3 takes up the same spots on your cells that T3 needs, so your cells stay slow. Thyroid antibodies can be rising for years before TSH changes. To understand what a TSH-only test misses, read normal TSH but still having symptoms.

Root cause 1: low iron and ferritin

Iron does two jobs that matter here. It carries oxygen in your blood to the cells that make heat. It also helps the enzyme that builds thyroid hormone in the first place, and it helps your body convert T4 into T3.

A review in Critical Reviews in Food Science and Nutrition found that people low in iron struggle to hold their body temperature in the cold, and linked this to lower thyroid function and less heat production (1996 review).

Heavy periods, a plant-based diet, low stomach acid and gut inflammation can all drain your iron. Your hemoglobin can be normal while your ferritin, your iron stores, is low. Ask for ferritin, not just a blood count. If your labs keep coming back normal while you feel flat, read tired all the time but blood work is normal.

Root cause 2: missing thyroid nutrients

Your thyroid needs raw materials to make and convert its hormones:

• Iodine is the building block of thyroid hormone. Bromine and chlorine compete with it. Read more in our article on iodine and bromine.
• Selenium helps convert T4 into active T3 and protects your thyroid from oxidative stress.
• Zinc supports hormone production and conversion.
• Protein supplies tyrosine, the amino acid your thyroid hormone is built on.

Test before you supplement. Too much iodine or selenium can cause problems too, so the amount should match your results.

Root cause 3: under-eating and blood sugar swings

When you eat too little, skip meals or stay on a low-carb diet for a long time, your body reads it as a shortage. It saves energy by making more reverse T3 and less active T3. Your metabolism slows, and you feel colder.

Eat protein, fat and fiber at every meal. Do not skip breakfast. If you crash after meals, see what your energy crash after eating is telling you.

Root cause 4: stress and toxic load

High cortisol from long-term stress slows the conversion of T4 into T3 and raises reverse T3. Poor sleep makes it worse.

Toxins add to the load. Heavy metals, mold exposure and halogens like bromine can interfere with your thyroid and with the enzymes that activate its hormones. This is the toxicity side of the picture, and it is often missed when you only look at deficiencies.

A simple check you can do at home

Keep a thermometer by your bed. For five mornings, take your temperature under your arm before you get up or move around. Write it down. If you are still having periods, start on day two of your cycle.

A morning temperature that is often below 97.8°F can be one more sign that your metabolism is running slow. This does not diagnose anything. It gives you useful information to bring to your practitioner along with your labs.

Test first, then build your plan

The tests that tell you the most when you are always cold:

• A full thyroid panel: TSH, free T4, free T3, reverse T3, TPO antibodies and thyroglobulin antibodies.
• An iron panel with ferritin: serum iron, TIBC, transferrin saturation and ferritin.
• Nutrient levels: RBC magnesium, zinc, selenium and vitamin D.
• Blood sugar markers: fasting glucose, fasting insulin and HbA1c.
• A 4-point cortisol test if stress and poor sleep are part of your picture.

You can see the panels and pricing on the lab testing page.

Once you have your results, your plan addresses what is actually going on: deficiency (iron, iodine, selenium, zinc, protein), toxicity (metals, mold, bromine) and terrain (your gut, your liver and your stress load). That is how you support your thyroid to keep you warm, instead of piling on layers. The thyroid page explains how this works in Diana's practice.

If you take any prescription medication, including thyroid medication, make changes to it only with your prescribing practitioner's supervision.

Find out why you are always cold

If you have been cold for months and nobody can tell you why, start with your thyroid. Take the free root-cause quiz to see which of your body's systems is under the most strain, or book a free 15-minute call with Diana to talk through your symptoms and which tests make sense for you.