A woman looking worried, holding her neck with an illustration of her thyroid

15 Signs Of An Underactive Thyroid (Thyroid series part 2)

Hypothyroidism is when the thyroid gland is under active and doesn’t produce enough of the thyroid hormones, T3 and T4.

Hypothyroidism is when the thyroid gland doesn’t produce enough of the two thyroid hormones – triiodothyronine (T3) and thyroxine (T4) – and ignores the chemical signal, thyroid stimulating hormone (TSH), released by the brain to ramp up thyroid hormone production. The sluggishness of the thyroid is caused by an autoimmune reaction where the body destroys the enzyme thyroid peroxidase (TPO), which converts inactive T4 into active T3. 

The brain notices that the thyroid is being seemingly lazy and tries to whip it into action by releasing higher and higher levels of TSH. But it doesn’t work. It’s like trying to shout at an unfit person to run faster when they just can’t!

This autoimmune condition is called Hashimoto’s Disease. It is the most common cause of an underactive thyroid gland and affects 5% of the adult population in developed countries. It is up to ten times more common in women than men and most commonly occurs in women between the ages of 30 and 50. 

Other less common causes of thyroid underactivity can arise from tumours in the brain that interfere with the production of TSH.

What are the symptoms of hypothyroidism?

  • Weight gain
  • Depression
  • Constipation
  • Feeling cold all the time
  • Fatigue
  • Muscle weakness and joint pains
  • Hair loss from the scalp and outer edges of the eyebrows
  • Tingling in the hands and feet
  • Heavy periods, irregular periods and fertility problems
  • Hearing loss
  • Dry Skin
  • Puffiness of the hands, face or eye lids known as myxoedema
  • Swelling of the thyroid (goitre)
  • Hoarse voice
  • Bulging of the eyes (exophthalmos) 

What are the triggers for hypothyroidism?

  • Extreme emotional stress
  • Extreme physical stress
  • Extreme physiological stress such as infection or pregnancy 
  • Treatment for an overactive thyroid gland
  • Radiotherapy around the neck for other cancers
  • Other autoimmune disease such as coeliac disease, diabetes, lupus etc
A woman sitting on the floor holding her knees, looking stressed

What are the dangers of an underactive thyroid gland?

There are significant health risks for people with untreated hypothyroidism. 

Raised cardiovascular risk. Thyroid hormones play an important role in regulating cholesterol levels. When T3 and T4 levels are deficient, cholesterol levels rise, increasing the risk of developing heart disease.

Increased diabetes risk. An underactive thyroid gland is associated with weight gain which overtime can lead to pre-diabetes and type 2 diabetes.

Depression. Thyroid hormones are involved in the serotonin system in the brain. Serotonin is an important neurotransmitter that plays a critical role in mood regulation. Low levels of thyroid hormones are associated with reduced levels of serotonin leading to an increased risk of depression.

Infertility. Hypothyroidism can contribute to infertility in many ways. Low thyroid hormone levels affect menstrual regularity as well as ovulation. A drop in body temperature due to hypothyroidism can also make it harder to conceive. Once pregnant, women with hypothyroidism have an increased risk of miscarriage and having babies with birth defects. 

Myxoedema. This is a rare stage of very advanced hypothyroidism. All the symptoms of an underactive thyroid are very extreme leading to fluid build-up, kidney problems, heart failure and sometimes even death.  

How is hypothyroidism diagnosed?

This can be done by straight forward blood testing for the levels of TSH, T3 and T4. You would expect to see low levels of T3 and T4 which, through the negative feedback loop to the brain, would result in high levels of TSH. Antibody blood testing would reveal the presence of antibodies to the enzyme TPO which converts inactive T4 into active T3. Ultrasound of the neck might show some changes to the thyroid gland too. 

How is it treated?

The focus of treatment is to increase the levels of thyroid hormones back into the normal range. This is easily achieved with medications like levothyroxine which is a synthetic version of T4. The brain doesn’t recognize that the circulating T4 hasn’t been made by the thyroid and is actually coming from an external source. TPO can act on this synthetic T4 to convert it into active T3. So TSH levels also start to fall back into a more appropriate range. 

A table covered in fruits, nuts and vegetables

Things you can do

Stress Management. Stress is a major trigger for hypothyroidism. All types of stress can be improved with simple things you can build into your daily life. Here are some ideas.

Omega 3. There is evidence that omega 3 supplements can help settle the thyroid gland down by reducing inflammation. Consider fish oil supplements, vegan omega 3 supplements or use flax seeds in your food. 

Anti-inflammatory diet. Eat a diet rich in wholefoods with plenty of colourful veggies and fruit for their anti-oxidant effects. Use turmeric and ginger in your cooking. Avoid processed foods and excess refined sugars.

Nurture your gut bacteria. Looking after your microbiome is an important part of general wellbeing. Eat a diet high in fibre, with lots of plant-based variety. These are also known as pre-biotic foods and nourish the good bacteria in your gut. Try fermented foods like unflavoured yoghurt and sauerkraut or add in a pro-biotic supplement. 

Iodine. Iodine is a necessary component of thyroid hormones. Deficiency in iodine leads to deficiency in thyroid hormones. Ensure you’re having enough in your diet. Seaweed, seafood and dairy products are a good source of iodine. 

Selenium. Not only does selenium have anti-oxidant properties that reduce autoimmune activity in the thyroid, selenium also plays an important role in converting inactive T4 into active T3. Include brazil nuts, sunflower seeds, fish, lean animal proteins, mushrooms, brown rice, lentils and bananas in your diet to maintain selenium levels.

Zinc. Zinc supports the thyroid in two ways. First it is needed for the production of TSH. Zinc deficiency leads to lower TSH levels which in turn means the thyroid produces less T3 and T4. Zinc is also needed to make the enzyme that converts inactive T4 into T3. If you like oysters, they are the most potent source of dietary zinc. But you can also get zinc from lean red meat, poultry, beans, shellfish and nuts.


For more information on how the thyroid works and how you can protect it, read Part 1 of the Thyroid Series.

If you think you may have some of the symptoms in this article, ask your GP for a thyroid blood test. It’s quick, it’s easy and it gives enough information to know if you’re all clear or whether you might need some extra checks.

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