Thyroid Health: When Your Metabolism Needs Support

You are doing everything right - eating well, exercising, managing stress - but you still feel exhausted, cannot lose weight, and your brain feels like it is operating through fog. Or perhaps you are anxious, losing weight despite eating plenty, with a heart that races for no reason. Both scenarios could point to your thyroid.

This small, butterfly-shaped gland at the base of your neck has outsized influence on virtually every system in your body. When it is not functioning optimally, the effects ripple through your entire being.

What Your Thyroid Actually Does

Your thyroid produces hormones - primarily T4 (thyroxine) and some T3 (triiodothyronine) - that regulate your metabolism. But metabolism is not just about weight. Thyroid hormones affect:

• How quickly you burn calories and use energy
• Your body temperature
• Heart rate and cardiovascular function
• Digestion and gut motility
• Brain function, mood, and cognitive clarity
• Muscle strength and reflexes
• Skin, hair, and nail health
• Menstrual cycles and fertility
• Cholesterol levels

Every cell in your body has thyroid hormone receptors. When thyroid function is optimal, you feel energetic, clear-headed, and your body systems work smoothly. When it is off, the effects show up everywhere.

The Thyroid System Is More Than Just the Thyroid

Thyroid function involves a complex feedback loop. Your hypothalamus (in the brain) monitors thyroid hormone levels and signals the pituitary gland to produce TSH (thyroid-stimulating hormone). TSH tells your thyroid how much hormone to produce. Your thyroid primarily produces T4, which then gets converted to T3 (the more active form) in tissues throughout the body, especially the liver and gut.

Problems can occur at any point in this chain:

• The thyroid itself may not produce enough hormone (primary hypothyroidism)
• The pituitary or hypothalamus may not be signalling properly
• T4 may not be converting efficiently to T3
• Thyroid hormones may not be entering cells properly
• The body may be producing reverse T3 (an inactive form) instead of active T3

This complexity is one reason thyroid issues can be missed by standard testing, which often only measures TSH.

Hypothyroidism: When Everything Slows Down

Hypothyroidism (underactive thyroid) is more common than hyperthyroidism, particularly in women over 40. When thyroid hormone levels are too low, metabolism slows:

• Fatigue that does not improve with rest
• Weight gain or difficulty losing weight
• Feeling cold, especially in hands and feet
• Constipation
• Dry skin and hair, brittle nails
• Hair loss, including the outer third of eyebrows
• Brain fog, difficulty concentrating, memory problems
• Depression, low mood
• Muscle weakness, joint pain
• Heavy or irregular periods
• High cholesterol
• Puffy face, particularly around the eyes
• Slow heart rate

The most common cause of hypothyroidism in developed countries is Hashimoto's thyroiditis, an autoimmune condition where the immune system attacks the thyroid. Other causes include iodine deficiency (less common in developed countries), surgical removal of the thyroid, radiation treatment, and certain medications.

Hyperthyroidism: When Everything Speeds Up

Hyperthyroidism (overactive thyroid) produces the opposite picture - metabolism in overdrive:

• Anxiety, nervousness, irritability
• Rapid or irregular heartbeat
• Unintentional weight loss despite good appetite
• Increased sweating, heat intolerance
• Trembling hands
• Difficulty sleeping
• Frequent bowel movements
• Thin skin and fine, brittle hair
• Muscle weakness
• Light or missed periods
• Bulging eyes (in Graves' disease)

Graves' disease, another autoimmune condition, is the most common cause of hyperthyroidism. The immune system produces antibodies that overstimulate the thyroid.

The Testing Conversation

Standard thyroid testing often includes only TSH, sometimes with free T4. This can miss a lot. A fuller picture includes:

• TSH: The pituitary hormone that stimulates the thyroid. High TSH suggests the body is working hard to stimulate an underperforming thyroid. Low TSH can indicate hyperthyroidism.
• Free T4: The unbound, available T4 in your blood.
• Free T3: The active hormone. If T4 is normal but T3 is low, conversion may be impaired.
• Reverse T3: An inactive form. High reverse T3 can indicate conversion problems, often related to stress or inflammation.
• Thyroid antibodies (TPO and thyroglobulin): Elevated antibodies indicate autoimmune thyroid disease, even if TSH is still normal.

The reference ranges for these tests are controversial. What is considered "normal" may not be optimal for you. Some people feel best with TSH at the lower end of the range, while others tolerate higher levels. Working with a practitioner who looks at the full picture and considers your symptoms alongside lab values often yields better results than relying on standard reference ranges alone.

What Affects Thyroid Function

Beyond the thyroid gland itself, many factors influence thyroid function:

Nutrient status. The thyroid needs iodine to make hormones, selenium and zinc for T4-to-T3 conversion, iron for hormone production, and vitamin D for thyroid receptor function. Deficiencies in any of these can impair thyroid function even when the gland itself is healthy.

Gut health. A significant portion of T4-to-T3 conversion happens in the gut. Gut inflammation, dysbiosis, and intestinal permeability can impair this conversion. Additionally, many autoimmune thyroid conditions are connected to gut health - there is a strong association between celiac disease and Hashimoto's, for example.

Stress. Chronic stress increases cortisol, which inhibits T4-to-T3 conversion and promotes reverse T3 production. This is one reason you can feel hypothyroid during prolonged stress even with normal TSH.

Inflammation. Systemic inflammation impairs thyroid function at multiple levels. Addressing sources of inflammation - gut issues, food sensitivities, infections, blood sugar imbalances - can support thyroid health.

Blood sugar. Blood sugar dysregulation affects thyroid hormone conversion and can worsen thyroid symptoms.

Environmental factors. Certain chemicals disrupt thyroid function, including perchlorate, bromide, fluoride, and various endocrine-disrupting chemicals found in plastics, pesticides, and personal care products.

Estrogen dominance. High oestrogen relative to progesterone increases thyroid-binding proteins, which can leave less free hormone available to cells.

Supporting Thyroid Health

If you have a diagnosed thyroid condition, work with your healthcare provider on appropriate treatment. But even alongside medication, and certainly for supporting overall thyroid health, lifestyle factors matter:

• Ensure adequate intake of thyroid-supportive nutrients through food or supplementation if needed
• Address gut health issues that may be affecting conversion and absorption
• Manage stress to support healthy conversion
• Reduce exposure to thyroid-disrupting chemicals
• Maintain stable blood sugar
• Address inflammation and its sources
• Get adequate sleep
• Consider food sensitivities, particularly gluten, which has associations with Hashimoto's

Listening to Your Body

Thyroid symptoms are common - fatigue, weight changes, mood shifts. They overlap with many other conditions, which is why thyroid issues can be missed. But if you are experiencing a cluster of these symptoms, especially if they came on gradually or worsened over time, thyroid function is worth investigating.

Trust your experience. If you have been told your thyroid is "normal" but you still have symptoms, comprehensive testing and a practitioner who takes your symptoms seriously can make a difference. Normal is not the same as optimal, and your body is the ultimate measure of whether your thyroid is functioning well for you.

Want to explore connected topics? Learn about fatigue and its causes, understand stress and cortisol, or explore women's hormonal health.