What does the thyroid do?
The thyroid is a butterfly-shaped gland at the front of the neck. It makes hormones that help set the pace of many body processes, including how quickly you use energy, your heart rate, temperature and digestion.
What is an underactive thyroid?
Hypothyroidism means the thyroid isn't making enough hormone. It is more common in women and often starts between 30 and 50, though it can happen at any age.
Common causes:
- Hashimoto's thyroiditis, an autoimmune condition where the immune system attacks the thyroid (the most common cause in countries with iodised salt, including South Africa);
- previous thyroid surgery, radioactive iodine or radiotherapy to the neck;
- some medicines;
- temporary inflammation of the thyroid, including after pregnancy;
- iodine deficiency (now uncommon where salt is iodised).
A family history of thyroid or other autoimmune conditions raises your risk.
Symptoms
Symptoms often develop slowly and can be vague:
- tiredness and low energy;
- feeling cold;
- weight gain;
- constipation;
- dry skin and hair, or hair thinning;
- low mood and difficulty concentrating;
- heavy or irregular periods;
- a hoarse voice;
- muscle aches.
Because these symptoms are common and have many other causes, a blood test is the only way to know.
How much weight does it cause?
Weight gain from hypothyroidism is usually modest, often a few kilograms, and much of it is extra salt and water rather than fat. Treating it may lead to some weight loss, but often less than people hope.
If you have gained a lot of weight, other factors, such as sleep, stress, activity, diet, medicines, menopause or insulin resistance, are usually involved. These are worth exploring with your doctor too.
Which tests?
| Test | What it shows |
|---|---|
| TSH (thyroid-stimulating hormone) | The best first test. TSH rises when the thyroid is underactive, as the brain "shouts louder" at it |
| Free T4 | The main thyroid hormone; usually checked if TSH is abnormal |
| Thyroid antibodies | Can suggest Hashimoto's as the cause |
Subclinical hypothyroidism means TSH is mildly raised but T4 is normal. Many people with this don't need treatment, especially if TSH is only slightly high. It is usually rechecked, as results can return to normal.
Thyroid tests can be affected by acute illness, some medicines and supplements (for example biotin, found in some hair and nail products). Tell your doctor what you take.
Treatment
Hypothyroidism is usually treated with a daily thyroid hormone replacement tablet, with regular blood tests to get the dose right. Most people take it long term. Too much can cause a fast heart rate, anxiety, poor sleep and, over time, bone loss.
Thyroid hormone is not a weight-loss treatment
Taking thyroid hormone, or "thyroid support" supplements, when your thyroid is normal does not lead to healthy, lasting weight loss and can be dangerous, affecting heart rhythm and bones. Avoid products sold online or in salons that claim to "boost" your thyroid or metabolism.
When to see a doctor
- You have several of the symptoms above.
- You have a family history of thyroid disease or another autoimmune condition.
- You notice a swelling or lump in your neck.
- You're pregnant or planning pregnancy and have a thyroid condition.
Frequently asked questions
Can a normal thyroid test be wrong?
A normal TSH generally rules out hypothyroidism in people with a healthy pituitary gland. If symptoms persist, your doctor will look for other causes.
Does an overactive thyroid cause weight loss?
Often, yes, along with symptoms such as a racing heart, anxiety, tremor and heat intolerance. This also needs medical assessment.
Should I take iodine or selenium supplements?
Not unless your doctor advises it. Too much iodine can also cause thyroid problems.
Can my thyroid affect my cholesterol?
Yes. An underactive thyroid can raise cholesterol, which is why it is sometimes checked when cholesterol is high.
References
- NHS. Underactive thyroid (hypothyroidism): symptoms. https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/symptoms
- American Thyroid Association. Thyroid and weight. Patient information.
- NICE. Thyroid disease: assessment and management (NG145). 2019.
This article is for general educational purposes only, like a health newsletter. It is not medical advice, diagnosis or treatment, and reading it does not create a doctor and patient relationship. Please speak to your own doctor about your situation. In an emergency, call 10177 or 112, or go to your nearest emergency unit.