So many women in their 40s struggle with frustrating symptoms—fatigue, brain fog, mood swings, weight gain—and are left wondering: is this my thyroid, perimenopause, or both?
The truth is, symptoms of thyroid dysfunction (whether underactive or overactive) often mimic the symptoms of perimenopause—and vice versa. It’s no wonder so many women feel confused or even misdiagnosed.
Shared Symptoms: Why It’s So Confusing
Let’s look at just some of the overlapping symptoms:
- Heavy or irregular periods
- Fatigue and low energy
- Anxiety, depression, mood swings, irritability
- Brain fog
- Muscle and joint pain or weakness
- Gut issues like constipation
- Hot flushes or increased sweating
- Trouble sleeping or full-blown insomnia
- Hair thinning or hair loss
- Dry skin and brittle nails
- Low libido and lack of motivation
- Weight gain, especially around the middle
These are all classic signs of perimenopause, but also common symptoms of both hypothyroidism and hyperthyroidism.
Why Every Woman Over 40 Should Check Her Thyroid
If you’re over 40 and haven’t had a comprehensive thyroid panel recently, it’s time to get one. I recommend checking your thyroid at least once a year throughout your 40s and beyond—including postmenopause.
Here’s why: as we move from our cycling years into perimenopause and eventually into postmenopause, thyroid issues can emerge or worsen (perimenopause tends to amplify any pre-existing issues, whether known or unknown to you). And while it’s great that perimenopause is finally getting more attention, many women are missing an underlying thyroid issue, assuming it’s “just hormones.”
But often, it’s both.
Perimenopause can worsen thyroid function, and thyroid dysfunction can amplify perimenopausal symptoms. It’s a two-way street.
Why This Happens: The Hormone-Thyroid Connection
Several key factors explain this overlap:
- Declining progesterone can reduce thyroid hormone availability
- Erratic oestrogen levels can affect thyroid hormone binding
- Chronic stress and cortisol dysregulation reduce thyroid conversion
- Insulin resistance can block the conversion of T4 to T3 (active thyroid hormone)
Even if your thyroid blood results look “normal,” these hormonal shifts can impair your thyroid’s function behind the scenes.
Most Common Overlapping Symptoms to Look Out For
Here are some of the most common symptoms that both perimenopause and thyroid dysfunction share:
- Fatigue
- Brain fog
- Stubborn or unexplained weight gain
- Hair thinning or loss
- Mood changes: anxiety, depression, irritability
- Dry skin
- Poor sleep
- Constipation
How to Tell the Difference
How to tell whether your symptoms point more toward thyroid issues or perimenopause:
Clues it might be your thyroid:
- Low energy all day long, not just in phases
- Cold hands and feet, even when others feel warm
- Constipation or sluggish digestion
- Puffy face or general swelling
Clues it’s likely perimenopause:
- Irregular or changing periods
- Symptoms that shift from month to month
- Hot flushes and night sweats
The Problem with Standard Thyroid Testing
In the UK (and many other countries), standard thyroid testing through your GP usually includes only TSH and free T4. But these don’t give the full picture.
Here’s why limited testing can be misleading:
- TSH is a signal, not a hormone. It’s produced by the brain, not the thyroid.
- Free T4 must be converted into free T3 to be active—this isn’t always tested.
- Free T3 is the active hormone that powers metabolism and energy.
- Reverse T3 can block T3 at the cellular level but is rarely tested.
- Thyroid antibodies (like TPOAb and TgAb) can reveal early autoimmune issues such as Hashimoto’s, even when TSH is “normal.”
Lifestyle Foundations for Thyroid and Perimenopausal Health
Supporting your thyroid and hormones doesn’t have to be complicated. These foundational lifestyle strategies support both:
1. Balance Your Blood Sugar
Blood sugar stability is crucial. Big spikes and crashes can stress your system and worsen symptoms.
- Eat protein with every meal, especially breakfast
- Don’t skip meals if you’re feeling wired, tired or anxious
- Fast overnight for 12–14 hours, no more
- Reduce refined carbs and sugar
- Add healthy fats and fibre to keep energy steady
2. Manage Your Stress
Stress is one of the most common disruptors of thyroid and hormone health.
- Prioritise rest, not just sleep
- Switch intense cardio for gentle movement like Pilates, walking or yoga
- Try tools like breathwork, journaling, or nervous system support
3. Support Your Circadian Rhythm
Your endocrine system relies on good light exposure and sleep-wake cues.
- Get morning daylight within an hour of waking
- Dim lights and reduce screens in the evening
- Stick to a consistent sleep routine, even on weekends
4. Eat a Nutrient-Rich Diet
Your thyroid needs nutrients to function—especially in perimenopause.
- Protein: eggs, poultry, legumes, fish
- Healthy fats: olive oil, seeds, avocado, oily fish
- Colourful veg: for fibre, minerals and antioxidants
- Slow carbs: like oats, root veg, quinoa, brown rice
Key Nutrients for Thyroid Function
Certain nutrients are especially vital:
- Selenium – supports T4 to T3 conversion
Sources: Brazil nuts (1–2/day!), eggs, fish - Zinc – important for thyroid hormone production
Sources: red meat, shellfish, pumpkin seeds - Iodine – essential but must be balanced, especially with autoimmunity
Sources: seaweed, fish, dairy (use food-based only unless advised) - Iron, Vitamin D, Magnesium, Tyrosine, B12, Folate – all play supporting roles in thyroid function and energy production.
The Gut-Thyroid Connection
About 20% of your T4 is converted to T3 in the gut—so gut health is crucial for thyroid function.
- Chew your food well, and eat in a relaxed state
- Include plant fibre and fermented foods (if tolerated)
- Address bloating, IBS, reflux or irregularity with testing and support
- Reduce inflammatory foods and eat mindfully
Other Testing to Consider During Perimenopause
Beyond thyroid, other valuable tests include:
- Sex Hormones – progesterone, oestrogen, testosterone
(Timing matters! Track patterns rather than relying on one-off results) - Blood Sugar & Insulin – fasting glucose, insulin, HbA1c
(Even with a healthy diet, hormone changes can affect glucose control) - Cholesterol panel + Liver markers (ALT)
(These give insights into metabolic and cardiovascular health) - Cortisol and Adrenal Function – through saliva or DUTCH testing
(Helpful if you’re dealing with fatigue, insomnia, or anxiety) - Nutrient Status – ferritin, active B12, vitamin D, magnesium, zinc, folate
(Especially important if you’re vegetarian/vegan or have heavy periods)
Final Thoughts
Perimenopause and thyroid issues often show up at the same time—and many women are told they’re “fine” because standard testing misses the full picture. If your symptoms aren’t improving or you feel brushed off, trust yourself.
Comprehensive testing and targeted lifestyle support can help you get answers—and feel like yourself again!
If you need personalised support, I have a comprehensive 3 month 121 Nutritional Therapy package to help you navigate perimenopause with practical, personalised strategies. You can book a free discovery call via my website 🙂
