01The link

Thyroid and fatigue: a gland that sets the pace.

The thyroid is a small butterfly-shaped gland at the base of the neck. It makes two hormones, T4 (thyroxine) and T3, which set the speed at which your cells use their energy. They regulate body heat, heart rate, digestion, muscle strength and mental sharpness. Can thyroid problems cause fatigue? Directly: when hormone production drops, the whole body slows down, and tiredness is often the first sign people notice.

The conductor sits in the brain. The pituitary gland releases TSH, a hormone that tells the thyroid to get to work. When the thyroid slows down, TSH rises to push it back into action; when it speeds up, TSH falls. That is why TSH is the starting test: it often moves before the hormones themselves.

Thyroid fatigue has a signature: it is there as soon as you wake up, rest barely touches it, and it comes with other signs of slowing down. Tiredness that varies a lot from one day to the next points instead to other causes, which our guide to persistent fatigue goes through one by one.

02Symptoms

Underactive thyroid symptoms: what comes with the fatigue.

How does it feel to have an underactive thyroid? Like living in slow motion. People describe a heavy tiredness, a need for more sleep, feeling cold when everyone else is fine, a duller mind. These signs creep in over months, so gradually that they are often put down to work, age or winter for a long time.

Hyperthyroidism (an overactive thyroid) is tiring too, but in a different way: the body races, nights get shorter, the muscles of the thighs and arms tire quickly. How do you know if you have hypothyroidism or hyperthyroidism? The symptoms give a clue; a blood test settles it.

Brain fog deserves a special mention: struggling to find your words, forgetfulness, concentration that drops off in the middle of the day. It is a common sign of hypothyroidism, and it usually eases once the treatment is properly balanced. We cover it in detail in our guide to brain fog and in our article on concentration problems.

03Blood tests

Subclinical or overt hypothyroidism: the blood tests that settle it.

The diagnosis comes down to a blood test. France's national health authority (Haute Autorité de santé) recommends starting with TSH alone. If it is outside the normal range, free T4 is added, then, to look for an autoimmune cause, anti-TPO antibodies. Measuring T3 adds nothing to diagnosing hypothyroidism.

Subclinical hypothyroidism is common: TSH is slightly high, T4 still normal. Should it be treated? European guidelines generally suggest treatment when TSH is above 10 mIU/L. Below that, the decision is made case by case, depending on age, antibodies, plans for pregnancy and symptoms. A slightly high TSH is rechecked first: it varies from one sample to the next, and sometimes returns to normal on its own.

If fatigue is the main complaint, ask for tests for the other common causes at the same time: full blood count, ferritin, vitamin B12, vitamin D, blood sugar. A single blood test covers them all, and it stops you blaming everything on the thyroid. Our guide to persistent fatigue explains this basic check-up in detail.

04Still tired on treatment

Still tired on levothyroxine: five things to check.

“My TSH is normal, so why am I still exhausted?” The problem is real. In a large British survey, patients on levothyroxine with a normal TSH reported poorer well-being than people of the same age without thyroid disease. In practice, there are five things to check with your doctor, in this order.

If the fatigue persists despite everything, an endocrinologist can discuss other options: the 2012 European guidelines describe combining T4 and T3 as a possible trial, on an experimental basis, for some patients. Never change your dose on your own. For stress and exhaustion, read our guide on how to lower cortisol and our article on the signs of burnout.

05The tablet

Levothyroxine (Levothyrox): how you take it changes your day.

Does Levothyrox make you tired? At the right dose, levothyroxine provides the same hormone that a healthy thyroid makes. But it is absorbed less well than people think, and irregular absorption is enough to shift your TSH. The patient leaflet recommends taking the tablet in the morning, on an empty stomach, with a glass of water, at least thirty minutes before breakfast.

• Coffee waits: in an Italian study, an espresso drunk with the tablet or just after it clearly reduced its absorption. Leave at least thirty minutes between the two, longer if your TSH is struggling to settle.
• Iron and calcium at a distance: allow at least four hours between the tablet and an iron or calcium supplement.
• Stomach medicines: some antacids and proton pump inhibitors can interfere with absorption. Tell your doctor about them.
• Soya and fibre: a breakfast very rich in soya or fibre, eaten straight after, can also reduce it.
• Consistency: same time, same way, every day.

A change of brand or formulation is monitored the same way: TSH is checked in the weeks that follow. And if you forget a tablet, take it as soon as you remember during the day, without doubling the next day's dose. On the coffee side, our article on coffee on an empty stomach and the one on how long caffeine lasts help you time your first cup.

07In women

Thyroid in women: three times to watch.

Thyroid diseases affect women far more often than men, particularly Hashimoto's disease. This autoimmune thyroiditis is the leading cause of hypothyroidism in countries where iodine intake is sufficient, such as France. The immune system gradually attacks the gland, often for years before TSH starts to rise. Three stages of life call for particular attention.

These three stages have one thing in common: the tiredness is readily blamed on circumstances, the baby, the nights, age. Yet it deserves a simple blood test, especially if thyroid disease runs in the family. For your forties and beyond, our guide to perimenopause and our article on menopause fatigue take this chapter further.

08Without a thyroid

Living without a thyroid: fatigue after the operation.

After a total thyroidectomy, levothyroxine replaces all of the gland's production, for life. The first weeks are often tiring: the anaesthetic, healing, a dose that is still being found, sometimes radioactive iodine treatment after cancer. Most people then get back to a normal life. The adjustment simply needs time to settle.

A high TSH on Levothyrox, without a thyroid, most often means the dose is too low or the tablet is poorly absorbed: reread the rules from the previous chapter before your appointment. After cancer, the TSH target may be deliberately lower; the team looking after you sets it. Finally, tingling around the mouth or in the fingers, or cramps after the operation, can signal low calcium and should be reported without delay. The parathyroid glands, which regulate calcium, sit right against the thyroid and are sometimes weakened by the surgery.

09Nodules

Thyroid nodules and fatigue: what you need to know.

Can a thyroid nodule cause fatigue? Rarely on its own. Nodules are very common: ultrasound finds them in a large share of adults, more so with age and in women, and the vast majority are benign. Most of them change nothing about how the gland works.

When fatigue and a nodule go together, it is the thyroid's function that gets checked. A so-called “hot” nodule can produce too much hormone and cause hyperthyroidism; Hashimoto's thyroiditis can come with nodules and hypothyroidism. The work-up combines TSH and a neck ultrasound; depending on the size and appearance of the nodule, the doctor may suggest a fine-needle aspiration, which is quick and done during the appointment.

• A nodule that grows quickly or becomes hard to the touch.
• A hoarse voice that lasts more than a few weeks.
• Difficulty swallowing or breathing.
• Lymph nodes that swell in the neck.

These four signs should be shown to a doctor without waiting for your next check-up. Apart from them, a nodule found by chance is monitored, usually with a follow-up ultrasound. And if fatigue is the main issue, go back to the basic check-up in chapter 3: the cause often lies elsewhere.

10Day to day

Fatigue and thyroid: what to do day to day?

How do you fight thyroid fatigue? A well-adjusted treatment does most of the work; the rest happens during the day.

On your plate, the thyroid needs iodine, found in fish, dairy products and iodised salt. On the other hand, avoid iodine supplements and concentrated seaweed without medical advice: too much iodine can also throw the gland off balance. Cabbage and soya do not need to be banned when cooked and eaten in normal amounts.

Some plants act on thyroid hormones, such as ashwagandha: ask for advice before combining them with your treatment. Our article on ashwagandha precautions covers this. For the day, also read our article on the 4 pm slump and our guide on how many coffees a day is right.

11The 21-day plan

Get your energy back: a 21-day plan.

Changing all your habits in one week does not last. This plan introduces three per week, in the order in which they matter most when you live with a slow thyroid. Keep a fatigue diary from the first day to the last: a score from 1 to 10 in the morning, the afternoon and the evening. It will show your progress.

After three weeks, compare the first and last pages of your diary. If the fatigue is easing, keep these habits for another month to make them stick. If it is still strong, show the diary to your doctor, along with the list of what you take: it is the best starting point for reviewing the dose and completing the check-up.

Our formula

For everyday tiredness: our Energy formula.

Your treatment remains the foundation of everything. Alongside it, for everyday tiredness, we created Energy: cordyceps, maca, ginger and vitamin C, which contributes to the reduction of tiredness and fatigue. A caffeine-free formula that fits into the morning routine described above.

Food supplement, to be used as part of a varied and balanced diet and a healthy lifestyle. If you are being treated for a thyroid condition, ask your doctor for advice before taking any supplement.

12When to see a doctor

Thyroid and fatigue: when to see a doctor without waiting?

Thyroid diseases respond well to treatment, and the first appointment is with your GP. They can order the blood tests, adjust the treatment and refer you to an endocrinologist if needed. Bring your fatigue diary and the list of what you take.

If you are having dark thoughts, call Samaritans on 116 123, the free helpline in the UK and Ireland, open 24 hours a day.

Sources

1. French National Agency for Medicines and Health Products Safety, ANSM (2017). Levothyrox: information on the new formula; around 3 million patients treated with levothyroxine in France. Levothyrox patient leaflet (taken on an empty stomach, at least 30 minutes before breakfast).
2. French National Authority for Health, HAS (2023). Hypothyroidism in adults: diagnosis, treatment and follow-up. Summary sheet (in French).
3. Chaker L., Bianco A. C., Jonklaas J., Peeters R. P. (2017). Hypothyroidism. The Lancet, 390(10101), 1550-1562.
4. Jonklaas J. et al. (2014). Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid, 24(12), 1670-1751.
5. Pearce S. H. S. et al. (2013). 2013 ETA guideline: management of subclinical hypothyroidism. European Thyroid Journal, 2(4), 215-228.
6. Wiersinga W. M. et al. (2012). 2012 ETA guidelines: the use of L-T4 + L-T3 in the treatment of hypothyroidism. European Thyroid Journal, 1(2), 55-71.
7. Saravanan P. et al. (2002). Psychological well-being in patients on “adequate” doses of l-thyroxine: results of a large, controlled community-based questionnaire study. Clinical Endocrinology, 57(5), 577-585.
8. Stott D. J. et al. (2017). Thyroid hormone therapy for older adults with subclinical hypothyroidism. The New England Journal of Medicine, 376(26), 2534-2544.
9. Feller M. et al. (2018). Association of thyroid hormone therapy with quality of life and thyroid-related symptoms in patients with subclinical hypothyroidism: a systematic review and meta-analysis. JAMA, 320(13), 1349-1359.
10. Benvenga S. et al. (2008). Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid, 18(3), 293-301.
11. Alexander E. K. et al. (2017). 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid, 27(3), 315-389.
12. Durante C. et al. (2018). The diagnosis and management of thyroid nodules: a review. JAMA, 319(9), 914-924.
13. Hirshkowitz M. et al. (2015). National Sleep Foundation's sleep time duration recommendations. Sleep Health, 1(1), 40-43.
14. Commission Regulation (EU) No 432/2012: authorised health claims (vitamin C).