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What are the signs of an underactive thyroid?

| OCT 17, 2022

Written by registered Nutritionist Emma Bardwell

What is hypothyroidism?

Hypothyroidism is the result of an underactive thyroid. In essence it means your thyroid, a small gland found at the base of your neck, isn’t producing enough thyroid hormone for your body’s needs. One of the thyroid’s main functions is to help regulate weight, cell repair, body temperature and heart rate. Many of the body's functions slow down when the thyroid doesn’t produce enough of the thyroid hormones triiodothyronine (T3) and thyroxine (T4).

According to Thyroid UK, women are 10 times more likely than men to be diagnosed with hypothyroidism and the most common age to be affected is between 40 and 50.

Some studies suggest around 2.2 million people in the UK may have hypothyroidism and as many as 1 in 20 have some kind of thyroid dysfunction.

What are the causes of hypothyroidism?

There are a number of reasons why you might develop hypothyroidism. These include:

  • Hashitmoto’s disease (an autoimmune condition where the body attacks the thyroid)
  • Genetic dysfunction
  • Iodine deficiency
  • Selenium deficiency
  • Thyroid surgery
  • Radiation therapy

What are the signs of an underactive thyroid?

Symptoms of an underactive thyroid often begin so gradually that you might not notice them until the condition has progressed. It’s worth noting that a number of conditions mimic the symptoms of an underactive thyroid, including: 

  • Perimenopause / menopause
  • Sleep apnoea
  • Anaemia
  • Chronic stress
  • Insufficient sleep
  • Poor diet
  • Depression

 Symptoms of underactive thyroid

  • Tiredness
  • Weight gain
  • Low mood or depression
  • Breathlessness
  • Being sensitive to the cold
  • Dry skin
  • Dry, gritty eyes
  • Coarse and/or thinning hair
  • Muscle aches
  • Hoarse or croaky voice
  • Constipation
  • Muscle weakness, cramps and aches
  • Pins and needles in the fingers and hands (carpal tunnel syndrome)
  • Heavier and longer periods
  • Fertility problems
  • Loss of libido
  • Puffy face and bags under the eyes
  • Slow speech, movements and thoughts
  • Memory problems
  • Difficulty concentrating
  • Slow heartbeat
  • Slightly raised blood pressure/raised cholesterol
  • An enlarged thyroid gland (goitre), difficulty swallowing
  • Slowed growth (in children)

How do you diagnose an underactive thyroid?

The only accurate way of finding out whether you have a thyroid problem is to have a blood test. Your GP will most commonly test your thyroid stimulating hormone (TSH) levels.

There are also tests that can measure free T4 (FT4), free T3 (FT3), thyroid peroxidase antibodies (TPO) and thyroglobulin antibodies (TgAb) but some doctors are reluctant to test for anything more than TSH and free T4, arguing that it’s unnecessary. You may need to ask to be referred to see an endocrinologist if you want more detailed investigations. 

TSH tests also play an important role in managing hypothyroidism. They help your doctor determine the right dosage of medication. In addition, TSH tests are used to help diagnose a condition called subclinical hypothyroidism, which usually causes no outward signs or symptoms. In this condition, you have normal blood levels of T3 and T4, but higher than normal levels of TSH.

It’s worth noting that there are certain factors that can affect thyroid blood test results. One is the blood-thinning medication heparin. Another is biotin, a B vitamin common in hair and nail supplements. To be on the safe side, let your doctor know about any medications or supplements you take before having blood tests done.

Risk factors

Although anyone can develop hypothyroidism, you're at an increased risk if you:

  • are a woman
  • are older than 60
  • have a family history of thyroid disease
  • have an autoimmune disease, such as celiac disease
  • have been treated with radioactive iodine or anti-thyroid medications
  • received radiation to your neck or upper chest
  • have had thyroid surgery (partial thyroidectomy)
  • have been pregnant or delivered a baby within the past six months


Nutrition and lifestyle recommendation for general thyroid health

There are certain nutrients that are essential for normal thyroid function. In developed countries, thyroid disease from iodine deficiency has pretty much been eliminated by iodine additives in salt and food. However, the trend for Himalayan pink salt, the move away from eating fish and dairy, and the government’s guideline to reduce salt to help improve cardiovascular health means some people might not be getting enough iodine from their diet.  


Iodine can be found in many foods, including:

  • Seaweed
  • Fish
  • Shellfish
  • Dairy
  • Eggs 
  • Chicken

Eating a balanced diet and opting for iodised salt (check labels) makes taking supplemental iodine unnecessary. In fact, too much iodine for a prolonged period from certain seaweeds like kelp can cause goitres and in people with an underlying thyroid issue can actually cause hyperthyroidism (elevated levels of thyroid hormones).

Although iodine and selenium are important for thyroid health, it can be easy to take too much. Only supplement on the advice of a doctor, registered nutritionist or dietitian.


Thyroid hormones are made from tyrosine, an amino acid that we get from protein. Food sources of protein include: 

  • Meat 
  • Fish
  • Tofu
  • Eggs
  • Greek yoghurt 
  • Legumes



We need selenium to ‘activate’ thyroid hormones so they can be used by the body. Think about adding selenium rich foods to your diet such as:

  • Brazil nuts (just 2-3 a day can give you the recommended daily amount)
  • Tuna
  • Sardines
  • Eggs
  • Legumes like lentils, beans and chickpeas


Zinc is also important in the production of thyroid hormones. Good sources include:

  • Shellfish like oysters
  • Beef
  • Chicken
  • Pumpkin seeds 
  • Almonds 


Research shows a link between iron deficiency and hypothyroidism. Dietary sources of iron include:

  • Red meat
  • Eggs
  • Fortified cereals
  • Beans
  • Pulses
  • Tofu 


Goitrogens are compounds found in food which may interfere with thyroid function. They’re often found in the brassica family, such as cabbage, cauliflower, kale, bok choi and spinach, as well as millet, sweet potato and soya-based foods. However, cooking these foods can reduce goitrogen levels and consuming goitrogens is often only an issue when they are eaten in very high amounts or when there's an iodine deficiency present 


Nutrition and lifestyle recommendation for people with hypothyroidism

There's no hypothyroidism diet per se. While there are lots of blogs online about hypothyroidism diets, there's no evidence that eating or avoiding certain foods will necessarily improve thyroid function in people with hypothyroidism. 

If you have hypothyroidism, it does however make sense to eat a diet such as the Mediterranean diet that focuses on lowering inflammation. Work on optimising your gut health and eat a heart healthy diet that avoids high levels of trans and saturated fats - thyroid disorders can increase the risk of high cholesterol.

Soy, taken in large amounts, may have an impact on thyroid hormone production but won't cause hypothyroidism in people who are not also iodine deficient. The debate about soy and hypothyroidism has become confusing and context is crucial. 

According to the British Dietetic Association, there is no reason why people who have hypothyroidism already treated with Levothyroxine should not eat quantities of soy. Parts of the medical community continue to be concerned about soy products that contain oestrogen-like chemicals. They advise avoiding soy isoflavone supplements and protein powders/protein bars that are made with textured vegetable protein and soy protein isolate.

Much has been written about gluten and the autoimmune thyroid disease, Hashimoto’s. To date, no good scientific research has established that thyroid antibodies are normalised on a gluten-free diet. However, many people anecdotally report feeling better after removing or reducing gluten in their diet. There may be numerous reasons for this, not least because gluten is found in many highly processed foods so it stands to reason that removing them might make people feel healthier. It’s also suggested that having one autoimmune disease makes you more susceptible to further autoimmune issues. Some Hashimoto’s sufferers may also have undiagnosed coeliac disease. Naturally, eliminating gluten will help this cohort and alleviate symptoms.

Are there any supplements I should take?

Vitamin D is important for everyone to supplement if they live in the northern hemisphere. It’s especially needed in the winter months (October to March) and the UK government recommends at least 10 mcg (400 IU), although it is argued that elderly people, pregnant women and those with darker skin tones need more. To find out your levels and requirements, talk to a GP about getting tested or look for home test kits.

As mentioned earlier, it’s prudent to lower inflammation where possible. Omega-3 fatty acids play an important role in the diet for their anti-inflammatory effects, among other benefits to heart and brain health. If you’re not eating a couple of portions of oily fish a week, it may be worth looking at a good quality fish oil or algae oil supplement.


Medical treatment for hypothyroidism

Standard treatment for hypothyroidism is Levothyroxine. This synthetic hormone restores hormone levels and reverses signs and symptoms of hypothyroidism. Most people feel better soon after starting treatment. The medication can also positively influence cholesterol levels and may help with weight gain. To ensure the correct dosage of Levothyroxine, you’ll need to have your TSH levels tested every year.

Levothyroxine absorption

Certain medications, supplements and even some foods may affect your ability to absorb Levothyroxine. 

Talk to your doctor if you:

  • Take iron supplements or multivitamins that contain iron
  • Take aluminium hydroxide, which is found in some antacids
  • Take calcium supplements
  • Eat a lot of soya based foods

Levothyroxine is best taken on an empty stomach at the same time every day. Ideally you need to wait at least an hour before eating or taking other medications. A 4-hour gap is often advised between taking Levothyroxine and iron supplements[1] or Levothyroxine and calcium-rich foods and supplements[2]If you’re in any doubt, talk to your GP or a registered nutritionist or dietitian.

If you’re in any doubt, talk to your GP or a registered nutritionist or dietitian.


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