Thyroid Health and Running Performance - She Runs Eats Performs

Episode 65

Published on:

19th Aug 2021

Thyroid Health and Running Performance

Thyroid Health and Running Performance


Thyroid dysfunction is very common, especially in women. Did you know that in the US approx. 20 million people have some form of thyroid dysfunction? BUT at least 60% of that number are unaware they have a condition.

Also, women are approx. 5%-10% more likely than men to develop a thyroid condition and it is thought that 1/8 women will develop a thyroid issue in their lifetime. 

Per capita, the figures are thought to be similar in the UK.…. those are quite phenomenal figures so, let’s explore:

1.     The thyroid gland and its function

2.     Thyroid dysfunction and its impact on running performance

3.     Some nutrition and lifestyle factors to support thyroid health.  

Show Notes


An outline of Thyroid Function:

The thyroid is a butterfly-shaped endocrine gland that sits on the front of the neck just below the Adam’s apple. It is made up of two lobes – which lie on either side of the wind-pipe, joined by a small bridge of thyroid tissue called the isthmus. Each lobe is about the size of a plum cut in half

The thyroid makes two hormones that it secretes into the blood stream, thyroxine (commonly known as T4) and triiodothyronine (known as T3)

The hypothalamus and pituitary gland located in the brain are the master regulators of the whole endocrine system within the body, which controls ALL hormone production

Regarding thyroid hormone production, the hypothalamus sends instructions to the pituitary gland by releasing thyrotropin-releasing hormone (TRH). The pituitary gland in turn sends instructions to the thyroid gland via thyroid stimulating hormone (TSH). The thyroid then produces and releases T3 and T4

This cascade is regulated by a negative feedback loop. What that means is: When circulating levels of thyroid hormone are high, the hypothalamus decreases its production of TRH, which in turn decreases the pituitary production of TSH, and thus inhibits production of T3 and T4. 

When circulating levels are low, the opposite effect takes place in which the hypothalamus signals the pituitary to further stimulate thyroid hormone production. 

The thyroid normally secretes roughly 20% of the body’s T3, but ALL of the internally produced T4. T4 is converted to the more metabolically active T3 in tissues throughout the body via a series of different enzymes. 


Key functions of the Thyroid Gland and its hormones (T4 and T3) associated with running performance:

  1. Metabolic rate - Most of us will be aware of their importance in maintaining metabolic rate. T4 and T3 control metabolism (i.e. the way the body uses energy) by regulating the speed with which the body cells work. So, we could think of our bodies as being a car, and the thyroid hormones as the engine. Increased metabolic rate =  increase body heat production
  2. Energy expenditure - by regulating the rate at which energy is burned. This can therefore affect weight loss or weight gain.
  3. Cardiac function – Thyroid hormones can slow down or speed up the heartbeat, they are also known to increase heart muscle contractibility and cardiac output. They are also known to promote vasodilation (widening of blood vessels), which leads to enhanced blood flow to many organs.
  4. Fat metabolism – thyroid hormones enhance utilisation of fatty acids in many tissues and are linked to plasma concentrations of cholesterol and triglycerides. E.g. when thyroid hormones are low, there is an increase in blood cholesterol concentration, in fact increased cholesterol levels is one diagnostic feature of hypothyroidism. 
  5. Carbohydrate metabolism: Thyroid hormones stimulate almost all aspects of carbohydrate metabolism, including enhancing the entry of glucose into cells and increased gluconeogenesis (use of proteins to produce energy) and glycogenolysis (conversion of stored glycogen) to generate free glucose.
  6.  Central nervous system - Both decreased and increased concentrations of thyroid hormones lead to alterations in mental state. Too little thyroid hormone, and the individual tends to feel mentally sluggish, while too much induces anxiety and nervousness.
  7. Muscle physiology – Thyroid hormones are required for skeletal muscle development but also their contraction and regeneration
  8. Bone – Thyroid hormones regulate bone formation and degradation (ie bone turnover) and bone mineral density. Normal thyroid hormone levels are also essential to maintain optimal bone strength.
  9. Body temperature – thyroid hormones can raise or lower body temperature. They regulate body temperature by increasing available energy in the body (so linked to energy expenditure), as well as by increasing appetite, pulse, the amount of oxygen delivered to different body parts, and fat buildup.
  10. Also, thyroid hormones work together with the nervous system in order to maintain body temperature.


Thyroid Test Reference ranges:


TSH: 0.45 – 4.5 µIU/mL

FreeT4: 0.82-1.77 ng/dL

FreeT3: 2.0-4.4 pg/mL

These are the standard ranges utilized by general medical bodies, however as Practitioners working within the Functional Medicine approach to health, we prefer to focus on optimal levels, which are:


TSH: 1.0-2.0 µIU/mL

FreeT4: 1.45-1.77

FreeT3: 3.4-4.2

Reverse T3: 9.2-24.1 ng/dL  (rT3 is the inactive form of T3, but it is very rarely tested for by GP or in hospitals, but can help determine how much bioavailable Thyroid hormone is available).

Thyroid antithyroglobulin antibodies (TAA): Less than 20 IU/mL

Thyroid perioxidase antibody (TPO): Less than 35 IU/mL


Thyroid Dysfunction;

Basically, this is when the thyroid gland releases an inappropriate level of thyroid hormones; either too much (known as hyperthyroidism) or too little (known as hypothyroidism). 

There are many different causes of thyroid dysfunction including:

For Hypofunction:

  • Thyroid gland failure – due to thyroid removal, radiation to thyroid for certain conditions (e.g. Graves), autoimmune destruction (i.e.Hashimoto’s Thyroiditis)
  • Insufficient thyroid gland stimulation by the hypothalamus or pituitary gland
  • Medications – e.g. lithium, Cold and sinus medication
  • Iodine deficiency – although not common in the western world
  • Other nutrient deficiencies including: iron, selenium
  • This will result in insufficient thyroid hormone production and secretion
  • Additionally, stress of intense training is thought to affect thyroid function too.

For Hyperfunction:

  • Thyroid hyperstimulation (often caused by multinodular Goitre – hyperfunctioning nodules)
  • Hyperfunctioning thyroid adenomas - benign thyroid lesions
  • Subacute thyroiditis: Inflammation of the thyroid that causes the gland to "leak" excess hormones, resulting in temporary hyperthyroidism that generally lasts a few weeks but may persist for months.
  • Pituitary gland malfunctions or cancerous growths in the thyroid gland: Although rare, hyperthyroidism can also develop from these causes.
  • Hypothyroid medication – ie. too high a dose of levothyroxine – medication needs to be monitored closely to prevent this occurring. 
  • Other medication: e.g. amiodarone (heart medication)

This will result in over production and secretion of thyroid hormone

Common signs and symptoms for thyroid dysfunction?

Hypersecretion of thyroid hormones:

  • Weight loss (despite increased appetite)
  • Palpitations
  • Heat intolerance
  • Insomnia
  • Tremor
  • Loose stools
  • Muscle weakness

More severe symptoms include: a rapid heartbeat. Irregular rate and rhythm of heartbeat, fever

Hyposecretion of thyroid hormones:

  • Weight gain
  • Fatigue
  • Muscle pain/weakness
  • Low mood/depression
  • Impaired sleep
  • Cold intolerance
  • Constipation
  • Dry skin
  • Hair loss


The impact of thyroid dysfunction on running performance:

If hypothyroidism is the concern, this may impact a runner due to:

  • Bradychardia (low heart rate) leading to decreased exercise tolerance and athletic performance
  • Muscle weakness - This is thought to be linked to decreased protein turnover and impaired CHO metabolism (which we mentioned earlier). 
  • Poor muscle contraction/relaxation leading to poor performance, recovery and increased risk of injury – this is thought to be caused by muscle weakness. 
  • Increased risk of fracture due to poor bone turnover and reduced bone mineral density
  • Reduced sub-maximal exercise capacity (so, running without too much effort) – this appears to be associated with iron deficiency and its impact on thyroid function.

If hyperthyroidism is the concern, this may impact a runner due to: 

  • Increased Basal Metabolic Rate – leading to heat-related illness due to increased oxygen consumption and heat production.
  • This same process is also thought to possibly lead to Rhabdomyolysis (a life-threatening condition caused by muscle breakdown and muscle death) and resulting from depleted muscle energy stores……although this is rare. 
  • Atrial fibrillation (rapid and irregular heart rate) and atrial flutter (a short circuit in the heart causing the upper chambers (atria) to pump very rapidly) - are a concern, especially as they could increase the risk of a stroke occurring but also because this population group may not present with an overt tachycardia (fast heartbeat) because, if well-conditioned, the would have a resting bradycardia (slow heartbeat). 
  • Muscle weakness – and an overall loss of muscle mass due to muscle fibre breakdown (atrophy)
  • Soft tissue – there appears to be an increased prevalence of frozen shoulder (adhesive capsulitis) in individuals with hyperthyroidism, which for a runner may lead to time away from training. 
  • Increased risk of fracture – due to increased bone turnover as a result of increased osteoclast-mediated bone resorption (osteoclast breakdown bone), which is as a result of increased resorptive time and decreased mineralization time. Also, increased risk of fracture due to reduced BMD and increased risk of osteoporosis caused by compromised bone turnover.  



  1. Women are approx. 5%-10% more likely than men to develop a thyroid condition
  2. Female runners (and athletes in general) are known to be at higher risk of overtraining syndrome (a subject we have discussed in a previous episode). Now overtraining syndrome causes amenorrhea (cessation of menstruation), which is known to lead to thyroid dysfunction
  3. Female athletes with hypothyroidism and accompanying menstrual irregularities could be suffering from FAT/REDs – disordered eating alongside hypothyroidism and menstrual dysfunction would help diagnosis this. This is generally driven by chronically poor energy status.


Nutrition interventions to support thyroid health:

To help support hypofunction:

  1. Introduce sea vegetables - Examples include: dried Dulce, Nori, Wakame (Clearspring have a good range), spirulina powder, and fresh sea asparagus (Samphire). Sea vegetables are important sources of iodine, which is important for the production of T4. 
  2. Lightly cook all cruciferous vegetables. Examples include: broccoli, cabbage, cauliflower, mustard greens, Brussels sprouts, kale and turnips. These vegetables contain goitrogens. Goitrogens are natural substances found in cruciferous vegetables and known to compete with iodine for uptake by the thyroid. This in turn results in a reduction of available iodine for T4 production. 
  3. Increase intake of iron rich foods DAILY. Examples include: kelp, nuts/seeds, green leafy vegetables eg. Spinach, parsley, beetroot greens, Swiss chard. Iron is required in the enzyme activity of T4 production. NOTE: lightly cook or blanche vegetables before eating. They contain natural substances (phytates) known to reduce iron absorption. Additionally, soaking nuts/seeds before consumption will neutralise their phytate activity, therefore increase iron absorption. 
  4. Introduce foods rich in B vitamins. They are required for the production of thyroid hormones. Examples include: wholegrains, nuts/seeds, leafy green vegetables, protein rich foods.
  5. Consume vitamin C rich foods alongside iron rich foods. This helps increase the absorption of iron. Examples include: bell peppers, cruciferous vegetables (see above), watercress, strawberries, papaya.
  6. Introduce foods rich in selenium - the thyroid is the organ that has the highest concentration of selenium in the body. This mineral plays a key role in the thyroid gland’s ability to produce thyroid hormone. Examples include: Brazil nuts (limit daily intake to 3), meat, fish, poultry, eggs are all good sources.

To help support hyperfunction:

With hyperfunctioning of the thyroid gland, generally intervention is necessary

BUT, there are some dietary approaches that could be introduced to help limit the effects of thyroid overstimulation including:

  1. Limit caffeine intake – caffeine is a stimulant and is known to stimulate the thyroid gland 
  2. Limit iodine containing foods, such as the ones we have mentioned already. Also, not so much in the UK, but in the states avoid iodised salt and any other foods fortified with iodine. Also, food preservatives may contain iodine so avoid these too. 
  3. Limit selenium rich foods e.g. meat. Fish, poultry, eggs. 
  4. A vegetarian/vegan diet may be supportive. One study (The Adventist Health Study-2) observed that hyperthyroid prevalence was 52% lower in vegans than in omnivores and 35% lower in vegetarians compared to omnivores suggesting that limiting meat/fish intake may be supportive in sub-clinical hyperthyroidism. 


Lifestyle factors to consider for Thyroid support:

  • Get sufficient sleep – 7-9hrs per night
  • Manage your exercise load – not too intensive
  • Manage stress – this has been shown to be closely linked to thyroid function as well as adrenal function
  • Limit exposure to toxins e.g. mercury in dental amalgams, which is thought to be a risk factor for autoimmune thyroiditis e.g. Hashimoto’s and food additives/preservatives



  1. The thyroid is a butterfly-shaped endocrine gland that sits on the front of the neck just below your Adam’s apple and it produces and secretes two hormones: thyroxine (commonly known as T4) and triiodothyronine (known as T3).
  2. Thyroid hormones have many functions but the ones that may directly or indirectly affect a runner and their running performance include: Metabolic rate energy expenditure, bone health and cardiac and muscle function.
  3. Thyroid dysfunction is when the thyroid gland releases an inappropriate level of thyroid hormones…either too much (known as hyperthyroidism) or too little (hypothyroidism). 
  4. Hyperthyroidism may present with symptoms including: Weight loss (despite increased appetite), Palpitations, Heat intolerance, Insomnia, Muscle weakness
  5. Hyperthyroidism may present with symptoms including: Weight gain, Fatigue, Muscle pain/weakness, Low mood/depression, Hair loss
  6. For a runner, thyroid dysfunction may lead to:  poor training, poor recovery from training, inability to carry out intensive training and/or long duration training, increase their risk of a stress fracture ansd muscle damage. 
  7. BUT a runner can support thyroid health by introducing some nutritional and lifestyle principles into their daily life including: appropriate amounts of key nutrients such as iron, selenium and iodine, limiting intake of animal foods, limiting caffeine intake and managing stress and exercise load. 

Related Episodes:

Food For Metabolism

Bone health Part 1

Bone Health part 2


The suggestions we make during this episode are for guidance and

advice only, and are not a substitute for medical advice or treatment.

If you have any concerns regarding your health, please contact

your healthcare professional for advice as soon as possible.

Aileen Smith and Karen Campbell met at as nutrition students (Institute for Optimum Nutrition, London) and became lifelong friends and nutritional buddies! Both have a love of running and a passion for nutrition, delicious food and healthy living.

Together they host RUNNERS HEALTH HUB. A place for like-minded runners who are looking for simple ways to support running performance, energy, endurance, and general great health.

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Aileen and Karen

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About the Podcast

She Runs Eats Performs
for mid-life female runners of all abilities
Are you confused about the science around nutrition for runners? Listen in to learn about the WHY, HOW, WHAT, and WHEN of eating to fuel your running performance.

We are here to help you translate sports nutritional science, into easy to apply tips and plans, helping you enjoy peak running performance. We focus on the FEMALE FACTORS every mid-life woman needs to know to be a healthy runner.

About your host

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Aileen Smith

Nutritionists, Educators, Podcasters, Runners and Friends

We have a love of running and a passion for nutrition, delicious food and healthy living. She Runs Eats Performs for female runners of all abilities who are looking for simple ways to improve their running performance and their health with nutrition and lifestyle.
We enjoy sharing our nutritional expertise, reviewing the latest sports science and most of all helping you to take easy action so you can enjoy your running life to the full.
We are here to help you achieve great health and good shape whilst staying injury-free with easy-to-understand sports nutritional concepts and easy-to-implement tips and plans.

Aileen and Karen are BANT and CNHC Registered Nutritional Therapists.