Underactive Thyroid Symptoms in Women, and Why a Normal TSH Can Miss It

By Tina Chagoury, Clinical Dietitian · 7 min read · 2026-09-27

Exhaustion, feeling cold, hair loss and weight gain are often blamed on stress or age. Sometimes they are your thyroid. Here is what to look for and what to test.

You sleep and still wake up tired. You are cold when everyone else in the room is comfortable. Your hair is coming out in the shower, your skin is dry, you are constipated, and the scale is creeping up although nothing about your eating has changed. You have been told it is stress, or age, or motherhood. Sometimes it is your thyroid. So let me walk you through the symptoms of an underactive thyroid in women, why a single test can miss it, and what you can actually do.

What the thyroid does

The thyroid is a small gland at the front of your neck. Its hormones set the pace of metabolism in almost every cell: your heart rate, your body temperature, how fast your gut moves, how quickly hair and skin renew, how much energy you have, and the rhythm of your cycle.

When it is underactive, a condition called hypothyroidism, everything slows down. That is why the symptoms are so broad, and why they are so easy to blame on something else.

Underactive thyroid symptoms in women

• Exhaustion that sleep does not fix.
• Feeling cold, especially in the hands and feet.
• Weight gain or difficulty losing weight, usually modest and partly fluid.
• Constipation.
• Dry skin, brittle nails and hair loss, sometimes including thinning of the outer eyebrows.
• A puffy face, especially around the eyes in the morning.
• Muscle aches, stiffness and joint pain.
• Low mood, slowed thinking and brain fog.
• Heavier, longer or irregular periods, and sometimes difficulty conceiving.
• Raised cholesterol on a routine blood test.
• A slow heart rate and a hoarse voice in some women.

None of these proves anything on its own. Many overlap with perimenopause, iron deficiency and depression, and that overlap is exactly why testing matters more than guessing. For the link with weight specifically, read can your thyroid explain your weight.

Why women are affected more

Women are far more likely than men to develop an underactive thyroid. The main reason is that its most common cause is autoimmune, and autoimmune conditions are much more common in women. It often appears after pregnancy and in the years around perimenopause, when shifting hormones influence immune activity.

Hashimoto's: the most common cause

Where iodine intake is adequate, the most common cause of an underactive thyroid in women is Hashimoto's thyroiditis. The immune system produces antibodies against the thyroid and gradually reduces its ability to make hormone.

Those antibodies, mainly TPO antibodies, can appear years before the standard markers move. Hashimoto's is an immune condition first, which is why gut health, inflammation, blood sugar and stress all matter alongside medication. I explain why in Hashimoto's is not just a thyroid problem.

Why TSH alone can miss it

TSH, thyroid stimulating hormone, is often the only test ordered. It is a signal from the pituitary gland in your brain asking the thyroid to work harder. It is a good screening test, and it is also indirect.

A fuller picture includes:

• TSH
• Free T4, the main hormone the thyroid makes.
• Free T3, the active form your cells use.
• TPO antibodies, and sometimes thyroglobulin antibodies, to look for Hashimoto's.

When TSH is mildly raised but T4 is still normal, doctors call it subclinical hypothyroidism. Whether to treat it depends on your symptoms, your antibodies, your age and whether you are planning a pregnancy, and that is your doctor's call.

Two practical points. Test at a consistent time of day, ideally in the morning. And if you take biotin, which is common in hair and nail supplements, tell your doctor, because it can distort thyroid results. They will tell you how long to stop it before the test.

The full reasoning is in why a normal TSH does not mean your thyroid is fine.

Iron, selenium and iodine, in general terms

Iron. Your thyroid needs iron to make its hormones, and low ferritin, meaning low iron stores, is very common in women with heavy periods. An underactive thyroid can itself make periods heavier, so the two can feed each other. Ask for ferritin alongside your thyroid panel, and if your iron never seems to recover, read why iron deficiency that never improves is telling you something.

Selenium. Involved in converting T4 into the active T3 and in protecting the thyroid. Fish, eggs and Brazil nuts are good sources. More is not better: too much selenium is harmful, so avoid high dose supplements unless your doctor advises them.

Iodine. The raw material for thyroid hormone. Too little and too much both cause problems, and in Hashimoto's, high dose iodine or kelp supplements can make things worse. Iodised salt, fish, eggs and dairy in normal amounts are enough for most women. Do not supplement iodine unless your doctor advises it.

Treatment is your doctor's decision

The standard treatment for an underactive thyroid is thyroid hormone replacement, most commonly levothyroxine. Your doctor sets and adjusts the dose based on your blood tests. Do not stop or change it on your own.

How you take it matters. Many women are advised to take it on an empty stomach, away from coffee, and separated from calcium and iron supplements, which reduce absorption. Follow your own doctor's or pharmacist's instructions. If you are pregnant or planning a pregnancy, tell your doctor straight away, because your needs change.

What nutrition can do

Nutrition does not replace thyroid medication. What it does is shape the environment your thyroid works in: enough protein, steady blood sugar, a calmer gut, lower inflammation and nutrients that are genuinely replete. Undereating is a stressor that can reduce conversion to T3, so chronic dieting works against you here.

You do not need to fear broccoli or cabbage. Cooked cruciferous vegetables in normal amounts are fine for almost everyone. The same goes for soy foods, as long as you keep them away from the time you take your tablet.

Working on that environment alongside your medical treatment is exactly what the Hormone Reset Method™ is built for.

When to see a doctor

• The symptoms above persist, especially several together.
• You notice a swelling or lump in your neck.
• You have a thyroid condition and are pregnant or trying to conceive.
• You feel exhausted and low in the months after giving birth.
• You have a family history of thyroid or autoimmune disease and new symptoms.
• Seek urgent care for extreme drowsiness, confusion, a very slow heart rate or severe swelling.

This article is nutrition education, not medical advice. Thyroid diagnosis and medication belong with your doctor or endocrinologist.

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About the author. Tina Chagoury is a licensed clinical dietitian specialising in women's hormonal health, inflammation and gut health, and the creator of the Hormone Reset Method™. Learn more about the Hormone Reset Method.

Frequently asked questions

What are the first signs of an underactive thyroid in women?

Tiredness that sleep does not fix, feeling cold, dry skin, constipation and hair shedding are often the first. They build slowly, which is why they are so easy to dismiss.

Can an underactive thyroid affect my periods?

Yes. It can make periods heavier, longer or irregular, and it can affect fertility. Thyroid testing is a standard part of investigating irregular cycles.

Can I treat an underactive thyroid naturally?

Not the hormone deficiency itself. If your thyroid is not making enough hormone, replacement prescribed by your doctor is the treatment. Nutrition, sleep and stress management support how you feel, and the immune side of Hashimoto's, alongside it.

Do thyroid tablets cause weight gain?

No. The right dose does not cause weight gain. Untreated hypothyroidism contributes to some gain, much of it fluid, and treatment usually brings a modest change rather than a dramatic one.

Why do I still feel unwell when my TSH is normal?

TSH alone can miss part of the picture. Ask about free T4, free T3 and antibodies, and check ferritin, vitamin D and B12, because low levels cause very similar symptoms.

Related reading

• Zinc and Selenium: Small Minerals With Outsized Roles in Hormonal Health
• Why Am I So Tired All the Time? Eight Things Worth Testing First
• Common Is Not the Same as Normal: 5 Symptoms Women Should Stop Living With