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Understanding Overactive & Underactive Thyroid

Updated: Dec 7, 2025

By Donna Burfield - Joy & Purpose Coaching

 

Your thyroid may be small, but it has a big job.


This tiny butterfly-shaped gland in your neck controls your body’s metabolism, your internal engine. When it’s working well, you might never think about it. But when it speeds up or slows down, everything from your mood to your weight to your energy levels can feel completely out of sync.

 

Thyroid conditions are common, often misunderstood, and frequently dismissed as “stress” or “burnout.” But your symptoms are real, and they deserve proper support.


 

Thyroid Conditions in the UK: The Reality

 

According to The British Thyroid Foundation, thyroid disorders affect 1 in 20 people in the UK, and many don’t realise for years.

 

  • Women are up to 10 times more likely to develop a thyroid condition than men.

  • Hypothyroidism (an underactive thyroid) is far more common than hyperthyroidism.

  • Autoimmune thyroid conditions often develop alongside other health issues, including menopause, perimenopause, and autoimmune disorders.

 

Thyroid symptoms can be subtle, overlap with other conditions, and vary from person to person, which is why so many cases go undiagnosed.


 

The Thyroid: A Quick Explanation

 

Your thyroid produces hormones (T3 and T4) that regulate:

 

  • metabolism

  • energy

  • heart rate

  • body temperature

  • digestion

  • mood

  • brain function

  • menstrual cycles

 

When this delicate balance is disrupted, the whole system feels it.


 

1. Underactive Thyroid (Hypothyroidism)

 

When the thyroid is underactive, it doesn’t produce enough hormones. This slows down the body’s “engine.”

 

Common Causes

 

  • Hashimoto’s thyroiditis (autoimmune) - the most common cause

  • Thyroid surgery

  • Radioiodine treatment

  • Genetic factors

  • Iodine deficiency (less common in the UK)

 

Symptoms of an Underactive Thyroid

 

Hypothyroidism can develop slowly, so symptoms often get dismissed as age, stress, or being “run down.”

 

Physical Symptoms

 

  • Fatigue or exhaustion

  • Weight gain

  • Cold intolerance

  • Dry skin and hair

  • Muscle aches

  • Constipation

  • Heavy or irregular periods

  • Slow heart rate

 

Emotional & Cognitive Symptoms

 

  • Low mood

  • Anxiety

  • Brain fog

  • Memory problems

  • Reduced motivation

 

Other Common Symptoms

 

  • Puffiness around the eyes

  • Hoarse voice

  • Carpal tunnel syndrome

  • High cholesterol

 

This condition is treatable but requires long-term monitoring and medication (usually levothyroxine).


 

2. Overactive Thyroid (Hyperthyroidism)

 

When the thyroid is overactive, it produces too many hormones. This speeds up the body’s internal processes.

 

Common Causes

 

  • Graves’ disease (autoimmune) - most common

  • Thyroid nodules

  • Inflammation of the thyroid

  • Excess iodine

 

Symptoms of an Overactive Thyroid

 

Physical Symptoms

 

  • Unexplained weight loss

  • Heat intolerance

  • Rapid heartbeat or palpitations

  • Tremors

  • Sweating

  • Diarrhoea

  • Frequent urination

 

Emotional & Cognitive Symptoms

 

  • Anxiety

  • Irritability

  • Restlessness

  • Panic attacks

  • Difficulty sleeping

 

Other Common Symptoms

 

  • Eye problems (in Graves’ disease)

  • Muscle weakness

  • Hair thinning

 

Hyperthyroidism often requires medication, radioactive iodine, or as in some cases, surgery.


 

Autoimmune Thyroid Conditions

 

Autoimmune thyroid disease occurs when the immune system mistakenly attacks the thyroid.

 

Hashimoto’s Thyroiditis

Leads to an underactive thyroid. Symptoms worsen gradually.

 

Graves’ Disease

Leads to an overactive thyroid. It can cause eye issues such as bulging, dryness, or sensitivity.

 

Autoimmune conditions can run in families and often overlap with other autoimmune disorders like coeliac disease, vitiligo, lupus, and rheumatoid arthritis.


 

Why Thyroid Conditions Often Get Missed

 

The symptoms overlap with:

 

  • menopause or perimenopause

  • depression or anxiety

  • burnout

  • chronic fatigue

  • IBS

  • ageing

  • stress

 

Because symptoms develop slowly, many people adapt without realising something deeper is going on.

 

If your body doesn’t feel like “you,” it’s worth asking your GP for a thyroid blood test.


 

How Thyroid Issues Impact Daily Life

 

Thyroid disorders can affect:

 

  • mood and emotional stability

  • relationships

  • work performance

  • weight and body image

  • confidence

  • energy levels

  • sleep quality

  • exercise tolerance

 

Because they’re invisible illnesses, many people feel misunderstood, dismissed, or judged.


 

Tests & Diagnosis

 

Your GP can run a simple blood test checking:

 

  • TSH (thyroid-stimulating hormone)

  • T4 and T3 levels

  • Thyroid antibodies (for autoimmune causes)

 

If results are unclear, repeated or broader testing is needed.


 

Everyday Support That Helps

 

  • prioritising rest

  • gentle exercise suitable for your body

  • stress reduction

  • balanced nutrition

  • tracking symptoms

  • joining support groups

  • being honest with loved ones about your needs


 

UK Thyroid Support Organisations

 

 

Thyroid conditions can make you feel unlike yourself, exhausted one month, wired the next, emotional, foggy, overwhelmed, or unable to explain what’s happening inside your own body.

 

With the right treatment, the right information, and the right emotional care, life can become steadier, softer, and far more manageable again.



🌿 You can explore more free tools, articles, and supportive resources on the Joy & Purpose Coaching website.

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