If you've been exhausted no matter how much you sleep, struggling with weight that won't budge despite doing everything right, or living in a mental fog that makes even simple tasks feel heavy — your thyroid might be worth a closer look.

Not because something is catastrophically wrong. Not because you should panic.

But because the thyroid is one of the most quietly influential glands in the entire body, and when it's not working optimally, almost everything suffers. Energy. Metabolism. Mood. Skin. Cycles. All of it.

This is what I wish someone had told me earlier: thyroid health rarely gets the airtime it deserves in women's hormonal health conversations — even when it's central to the picture.

So let's change that. This is your comprehensive guide to understanding your thyroid: what it does, what goes wrong, what the signs actually look like, and what you can do to support it.

Your thyroid produces hormones that regulate your metabolism, energy, bone health, growth, and reproductive function — essentially acting as your body's central control dial.

The thyroid is a small, butterfly-shaped gland sitting at the base of your neck. Weighing less than 28g, it punches well above its weight. Its primary job is to produce two hormones — triiodothyronine (T3) and thyroxine (T4) — which travel through the bloodstream and influence nearly every cell in your body.

Think of it less like a single on/off switch and more like a volume dial for your entire system. Too low, and everything slows down. Too high, and everything speeds up. Getting it dialled to just the right level is what keeps your body functioning the way it should.

The thyroid doesn't work alone. It takes instructions from the pituitary gland — a pea-sized structure at the base of the brain — via a hormone called TSH (thyroid-stimulating hormone). When thyroid hormone levels drop, the pituitary sends out more TSH to prompt the thyroid to produce more. This feedback loop is elegant in theory. When it goes wrong, the impact cascades across your whole system.

Hypothyroidism is when the thyroid doesn't produce enough T3 and T4, causing the body's processes to slow down. It's significantly more common in women than men and often develops gradually over time.

An underactive thyroid — the clinical term is hypothyroidism — is one of the most prevalent thyroid conditions women face. When your thyroid hormone levels fall too low, your metabolism slows, your energy tanks, and a cascade of symptoms follows that are easy to dismiss or misattribute to something else entirely.

Here's what makes it particularly tricky: the symptoms develop slowly. Weeks, sometimes months, sometimes years. By the time they're obvious, many women have already adapted around them — assuming they're just tired, just stressed, just getting older.

Your body is trying to tell you something. These symptoms are not imagined and they are not inevitable.

Common hypothyroidism symptoms include persistent fatigue, unexplained weight gain, cold sensitivity, dry skin, hair loss, brain fog, constipation, low mood, and irregular periods.

The challenge with this list is that it overlaps significantly with other conditions — PCOS, perimenopause, iron deficiency, burnout. That overlap is precisely why thyroid function goes unchecked for far too long in so many women.

Symptoms to be aware of include:

• Persistent tiredness that isn't improved by sleep or rest
• Weight gain or difficulty losing weight even without dietary changes
• Sensitivity to cold — feeling cold when others around you don't
• Dry skin, brittle nails, and coarse or thinning hair
• Constipation or sluggish digestion
• Brain fog and difficulty concentrating
• Low mood or depression
• Muscle aches, weakness, or stiffness
• Slower heart rate
• Irregular or heavier menstrual cycles

In younger women and adolescents, hypothyroidism can present differently — sometimes as poor growth, delayed puberty, or irregular periods — which gets mistaken for normal developmental variation. For women of perimenopausal age, these exact symptoms are regularly (and incorrectly) attributed to the onset of menopause.

You're not imagining it. And you deserve a proper investigation, not a shrug.

Thyroid disease is diagnosed through a blood test called a thyroid function test, which measures TSH, T3, and T4 hormone levels. This is the only definitive way to confirm a thyroid disorder.

If you're experiencing the symptoms above — particularly if they've been persistent — it's absolutely worth seeing your GP and requesting a thyroid function test. This involves a simple blood draw that gives a clear picture of how your thyroid is functioning.

A few things worth knowing before you go:

• TSH levels are often tested first. A raised TSH suggests the pituitary is working overtime trying to stimulate an underperforming thyroid.
• Free T3 and Free T4 may be tested alongside to show how much active hormone is actually circulating.
• Thyroid antibodies (TPOAb) may be checked if autoimmune thyroid disease (Hashimoto's thyroiditis) is suspected.
• Biotin supplements can interfere with test results. If you're taking biotin — common in hair, skin and nail supplements — let your GP know before testing.

It's also important to know that results falling within the "normal" reference range don't always capture the full picture for every individual. If you still don't feel right despite being told your results are fine, advocate for a full thyroid panel, not just TSH alone.

Women with PCOS are significantly more likely to develop subclinical hypothyroidism than women without PCOS, and the two conditions share overlapping symptoms that can complicate diagnosis and management.

This is a connection that doesn't get nearly enough attention in clinical or public conversations about hormonal health.

Research published in 2025 found that subclinical hypothyroidism — a milder, earlier-stage form of underactive thyroid — was nearly three times more prevalent in women with PCOS (14.9%) compared to women without PCOS (5.3%) [Ach et al., 2025]. A systematic review and meta-analysis from 2024 further confirmed that subclinical hypothyroidism is at least twice as common in women with PCOS [PMC11921581, 2024].

The relationship runs deeper than shared statistics. Thyroid dysfunction can worsen insulin resistance — already a core feature of PCOS — and may further disrupt ovarian function and cycle regularity. At the same time, the hormonal environment of PCOS appears to influence thyroid antibody levels, with research showing higher rates of thyroid peroxidase antibodies (TPOAb) in women with PCOS compared to controls [Ach et al., 2025].

In practice, this means: if you have PCOS and you're still struggling with fatigue, weight, or cycle irregularities despite addressing your PCOS directly, thyroid function is worth investigating. These two conditions can and do co-exist — and managing both leads to meaningfully better outcomes for metabolic health, fertility, and overall wellbeing.

The research on this is actually pretty clear: thyroid screening should be a standard part of the conversation for women with PCOS. If it hasn't come up in your care, it's absolutely worth raising.

The primary treatment for hypothyroidism is daily levothyroxine — a synthetic form of thyroxine — taken orally to restore hormone levels to normal. Dosage is individually calibrated through regular blood testing.

Once hypothyroidism is confirmed, treatment typically begins with a daily tablet of levothyroxine. This is a synthetic version of the T4 hormone your thyroid isn't producing in sufficient quantities. It's absorbed into the bloodstream, where the body can convert it to active T3 as needed.

Finding the right dose takes time. Blood tests are done regularly in the early stages to adjust the dosage until levels stabilise. Once optimal, most people move to annual monitoring.

A few important notes on levothyroxine:

• Take it consistently — ideally on an empty stomach, 30-60 minutes before food or other medications
• Certain foods and supplements can affect absorption — more on this in the nutrition section below
• Hypothyroidism is typically a lifelong condition — treatment is usually indefinite, but with the right dose, most people feel significantly better
• Untreated hypothyroidism carries real risks — including heart disease, pregnancy complications, and in rare severe cases, a life-threatening condition called myxoedema coma

This is not a condition to leave unchecked. But with proper management, it is absolutely one that allows a normal, healthy, full life.

A varied, nutrient-rich diet that includes adequate iodine, selenium, and zinc gives your thyroid the raw materials it needs to produce and convert hormones effectively.

Your thyroid cannot do its job without the right building blocks. The research here is actually pretty clear: micronutrient deficiencies — particularly in iodine and selenium — directly impair thyroid hormone production and activation [Zimmermann & Köhrle, 2002].

Iodine is the essential building block of T3 and T4. Without enough of it, thyroid hormone production cannot function adequately. Deficiency is more common than people realise — particularly in vegetarians and vegans, as the most reliable dietary sources tend to be dairy products, fish, and seafood.

Good iodine sources include:

• Dairy products (milk, yogurt, cheese)
• White fish and seafood
• Eggs
• Seaweed in moderate amounts (with caveats — see below)

If you don't regularly consume dairy or fish, your iodine intake may be lower than optimal. This is worth factoring in, particularly if you're navigating thyroid or hormonal symptoms.

Selenium plays a crucial supporting role: it's required for the conversion of inactive T4 into active T3 — the form your body actually uses. It also acts as a powerful antioxidant that protects the thyroid gland from oxidative damage [Frontiers in Endocrinology, 2023].

Good selenium sources include:

• Brazil nuts (2-3 per day provides a meaningful amount)
• Tuna and sardines
• Eggs
• Legumes

Zinc is involved in thyroid hormone synthesis and in the binding of T3 to its cellular receptors. Sources include beef, chicken, shellfish, and legumes.

Goitrogenic foods (brassicas): This group includes kale, cabbage, Brussels sprouts, cauliflower, turnips, and sweetcorn. In very large quantities, these can interfere with iodine uptake by the thyroid. You do not need to avoid them — cooking significantly reduces their impact, and moderate consumption is absolutely fine.

Soya: Some evidence suggests soya may interfere with levothyroxine absorption. If you're on thyroid medication, a 4-hour gap between your medication and soya products is a reasonable precaution.

High-fibre foods: Too much fibre consumed at the same time as levothyroxine can impair its absorption. This isn't a reason to avoid fibre — it's a reason to be mindful of timing relative to your medication.

Kelp supplements: While iodine is essential, excessive iodine can place additional strain on the thyroid and be counterproductive. High-dose kelp supplements are best avoided unless specifically directed by a healthcare professional.

A varied whole-food diet should provide most of the nutrients your thyroid needs. Supplementation is most relevant for those with restricted diets, confirmed deficiencies, or difficulty meeting needs through food alone.

Hormonal literacy isn't complicated — it's just rarely taught. And part of that literacy is understanding that supplements aren't magic fixes, but they can genuinely help fill gaps that diet alone isn't covering.

If you eat a varied diet that includes fish, dairy, eggs, and a wide range of vegetables, you're likely getting adequate amounts of the key thyroid-supporting nutrients. But if you're vegan or vegetarian, iodine deficiency in particular is a real consideration — very few plant foods are reliable sources.

For women looking to cover their nutritional foundations more broadly, a well-formulated daily multivitamin can be a practical, low-complexity approach. MyOva Women's Multivitamin includes 150μg of iodine from kelp — in line with UK nutritional guidance — alongside selenium and other trace minerals that support enzyme function, metabolism, and antioxidant defence. It's not a treatment for thyroid conditions, but it gives your body the raw materials it often needs to function well.

Always speak with your GP or a registered dietitian before making significant changes to your supplement routine, particularly if you're currently on thyroid medication.

Sleep, stress management, and appropriate exercise all directly influence thyroid health — chronic stress in particular can suppress thyroid hormone production and worsen symptoms.

This is the section that gets left out of most thyroid health conversations. It shouldn't be.

Thyroid hormone production follows circadian rhythms. Poor or insufficient sleep disrupts this cycle, and chronic sleep deprivation has been associated with altered TSH levels over time. If you're managing thyroid symptoms, prioritising sleep isn't a soft recommendation — it's foundational.

Chronic stress elevates cortisol, which can suppress TSH secretion and interfere with the conversion of T4 into active T3. Elevated cortisol can also worsen autoimmune activity — relevant if you're dealing with Hashimoto's thyroiditis. Stress management is not a wellness luxury. It is a genuine physiological requirement for thyroid health.

Tools that genuinely help: breathwork, gentle movement, structured rest, time in nature, and — where needed — professional support.

Regular, moderate exercise supports healthy metabolism and thyroid function. The key word is moderate. Very high-intensity exercise without adequate recovery can place additional strain on your endocrine system. If you're training hard, build in proper rest and pay attention to how your body responds.

Hypothyroidism is an underactive thyroid — the gland produces too little hormone, slowing the body down. Hyperthyroidism is the opposite: an overactive thyroid producing too much, causing symptoms like rapid heart rate, weight loss, anxiety, and intolerance to heat. Both are diagnosed via blood tests and have distinct treatment pathways.

Hypothyroidism can contribute to weight gain by slowing metabolism and causing fluid retention — but it's rarely the sole cause of significant weight changes. Treating the thyroid condition generally helps, though weight management remains multifactorial. Expecting levothyroxine alone to resolve weight concerns sets an unrealistic expectation.

Yes. Thyroid hormones play a role in ovulation and menstrual regularity. An underactive thyroid can disrupt cycle patterns and may affect the ability to conceive. Thyroid function testing is an important step for women experiencing irregular cycles who are trying to conceive, ideally investigated alongside other relevant hormonal markers.

In most cases, yes — particularly when caused by autoimmune thyroid disease (Hashimoto's) or treatment-related thyroid damage. Some cases, such as postpartum thyroiditis or medication-induced hypothyroidism, can be temporary. Your GP will advise based on your individual situation and ongoing monitoring results.

For the most part, yes. The goal is a varied, balanced diet. The main practical considerations are around the timing of levothyroxine relative to food, and avoiding very high amounts of goitrogenic foods or supplemental iodine. If you have specific questions about your diet and medication, a registered dietitian can provide personalised guidance.

If you're experiencing several of the symptoms described in this guide — particularly persistent fatigue, unexplained weight changes, sensitivity to cold, irregular periods, or low mood — make an appointment and ask your GP specifically for a thyroid function test.

Don't wait until symptoms feel unbearable. The test is a straightforward blood draw, and catching thyroid dysfunction early means earlier, more effective management.

If you also have PCOS, make thyroid screening a regular part of your health conversation. The research is clear that the two conditions are linked — even if that connection isn't always raised proactively in clinical settings.

Your diagnosis is a starting point, not a verdict. Whether it's PCOS, hypothyroidism, or both — understanding your full hormonal picture is where meaningful change begins.

• The thyroid is a small but powerful gland that regulates metabolism, energy, mood, menstrual cycles, and much more
• Hypothyroidism (underactive thyroid) is significantly more common in women and typically develops gradually — making it easy to miss
• Symptoms overlap with PCOS, perimenopause, and burnout — a thyroid function test is the only definitive diagnostic tool
• Women with PCOS are at meaningfully higher risk of subclinical hypothyroidism and should consider routine thyroid screening
• Key thyroid-supporting nutrients include iodine, selenium, and zinc — particularly important for women on vegan or vegetarian diets
• Treatment with levothyroxine is effective and well-tolerated for most people, allowing a normal and healthy quality of life
• Sleep, stress management, and moderate exercise provide meaningful additional support for thyroid function

1. Ach, T., Dhaffar, R., Ben Abdessalem, F., Saafi, W., Halloul, I., ElFekih, H., Saad, G., Hasni, Y. (2025). Subclinical Hypothyroidism in Polycystic Ovary Syndrome: Prevalence and Impact on Metabolic and Cardiovascular Risk. SAGE Open Medicine. https://doi.org/10.1177/11795514251343678

2. PMC11921581 (2024). Prevalence of subclinical hypothyroidism in polycystic ovary syndrome and its impact on insulin resistance: a systematic review and meta-analysis. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC11921581/

3. Zimmermann, M.B. & Köhrle, J. (2002). The impact of iron and selenium deficiencies on iodine and thyroid metabolism: biochemistry and relevance to public health. Thyroid, 12(10), 867–878. https://pubmed.ncbi.nlm.nih.gov/19594417/

4. Drutel, A., Archambeaud, F., Caron, P. (2023). Selenium and thyroid diseases. Frontiers in Endocrinology. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2023.1133000/full

5. NHS UK. Underactive thyroid (hypothyroidism). https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/

6. Kolodziejczyk, J. et al. (2025). Iodine and Selenium Status in Relation to Thyroid and Immune Functions in Women of Reproductive Age. PubMed Central. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12195968/

This article is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional regarding any health concerns or before making changes to your diet, supplementation, or treatment plan.