Perimenopause, or Is Something Else Going On?

Thyroid, Iron and Blood Sugar Explained

When you are lying awake at 3am, heart racing a little, feeling exhausted but somehow wired, have you ever wondered if what you are going through is actually perimenopause, or if there might be something else tangled up in the mix too?

I ask because this comes up in my inbox constantly. Women tell me they have started HRT, or cut out sugar, or tried every supplement going, and while some things have helped, they still do not feel quite right. And more often than you would think, the missing piece is not about their hormones at all, or not only about their hormones. It is their thyroid. Or their iron levels. Or insulin resistance quietly building in the background.

Here is the tricky part. Perimenopause, thyroid dysfunction, iron deficiency and insulin resistance can all produce almost identical symptoms, things like fatigue, brain fog, mood changes, weight gain and disrupted sleep. Even the experts say this overlap is one of the biggest diagnostic headaches in women's health, with researchers describing thyroid and menopause symptoms specifically as creating a genuine differential diagnosis challenge for doctors [1]. So if you have ever felt confused about what is actually going on in your body, please know it is not you being dramatic or overthinking it. This stuff is genuinely hard to untangle, even for clinicians.

So let us have a proper look at each of these, what the overlap actually looks like, and what you can do about it.

Perimenopause, or could it be your thyroid?

Your thyroid is a small butterfly shaped gland at the base of your neck, and it controls your metabolism, energy production, body temperature and even your mood. When it is underactive, a condition called hypothyroidism, the symptoms read almost like a checklist for perimenopause, fatigue, weight gain, low mood, hair thinning, dry skin, sleep disturbance, brain fog and even low libido and vaginal dryness [1].

Here is what makes this even more complicated. Thyroid problems become more common in the exact years that perimenopause is happening. Subclinical hypothyroidism, a milder form where your levels are just starting to drift, affects somewhere between 6-10% of women during their reproductive years, and this often continues or first appears during the menopause transition itself [1]. Because there are usually no obvious physical signs like a visibly swollen thyroid, doctors are genuinely being urged to keep a low threshold for testing and to order proper hormone panels whenever a midlife woman presents with these kinds of symptoms, rather than assuming it is menopause by default [1].

The takeaway here is simple. If you are ticking a lot of these boxes, ask your GP for a full thyroid panel, not just a basic TSH test, but free T4 and thyroid antibodies too, so nothing gets missed.

Perimenopause, or could it be iron deficiency?

This one genuinely surprises a lot of women, but it shouldn't, because perimenopause often comes hand in hand with heavier, longer or more unpredictable periods, and that means more blood loss and more risk of running low on iron.

Recent research using data from the well known Study of Women's Health Across the Nation found that over a six month period, around 1 in 5 women experienced at least one episode of heavy bleeding, and almost a quarter experienced prolonged bleeding lasting eight days or more [2]. And here is the part that really matters for how you are feeling day to day, women who had three or more heavy bleeding episodes were 60% more likely to report feeling tired and 44% more likely to feel worn out, compared with women who did not experience that heavy bleeding [2].

On top of that, iron deficiency is simply common in women of reproductive and perimenopausal age. Recent United States data shows anaemia affects around 14% of women aged 20 to 59, and the rate of anaemia among women aged 15 to 49 has actually been climbing, from 7.8% in 2000 up to 11.5% in 2018 [3]. Among physically active women specifically, iron deficiency can affect anywhere from 15-50%, and the documented effects include fatigue, low mood, reduced concentration, poor thermoregulation and reduced tolerance for exercise [4], all things that sound remarkably like a bad perimenopause day.

If you are feeling wiped out, foggy, breathless on the stairs, or noticing your hair coming out more than usual, it really is worth asking your GP for full iron studies, including ferritin, rather than just a standard full blood count. Ferritin is your iron storage marker, and it can be quietly low well before you become officially anaemic.

Perimenopause, or could it be insulin resistance?

This is the one I think deserves so much more airtime, because it works both ways. Insulin resistance, where your cells stop responding properly to insulin and your blood sugar and insulin levels creep upward, can absolutely mimic perimenopause on its own, with symptoms like fatigue, especially that heavy, sluggish feeling after meals, stubborn weight gain around the middle, sugar cravings, difficulty losing weight no matter what you try, and brain fog.

But here is the genuinely fascinating bit. New research has found that insulin resistance does not just look like perimenopause, it can actually make your real perimenopause symptoms worse. A 2025 study following women through the menopause transition found that higher fasting insulin levels in early perimenopause predicted an earlier onset of hot flushes and night sweats, and a longer duration of both [5]. In other words, if your insulin is creeping up quietly in the background, you may end up with more intense and longer lasting hot flushes as a direct result. The same body of research has found that women reporting hot flushes tend to show greater insulin resistance, independent of their age or their reproductive hormone levels [6], and that the odds of developing metabolic syndrome, a cluster of issues including insulin resistance, are actually highest specifically during perimenopause, again independent of age [6]. Body composition shifts around this time too, with research showing fat accumulation roughly doubling in the two years before your final period, while muscle mass quietly declines [6].

So this is not a separate, unrelated issue happening at the same time as perimenopause. For a lot of women, insulin resistance and hormonal changes are genuinely feeding into each other, which is exactly why addressing your blood sugar can make such a noticeable difference to how you feel. A simple fasting glucose and fasting insulin test, or a HbA1c, through your GP can give you a really useful starting point.

So what do you actually do with all this?

Firstly, please do not try to diagnose yourself from a blog, mine included. Take this information to your GP and ask, kindly but firmly, for the full picture, thyroid panel, iron studies with ferritin, and fasting glucose and insulin. These are simple blood tests, but they are not always offered as standard, so you may need to specifically ask.

Once you know what you are actually dealing with, this is where our four pillars approach comes in beautifully, because whether it turns out to be perimenopause, thyroid, iron, insulin resistance, or very often some combination of all of them, the daily habits that support you are wonderfully similar.

On the nutrition side, prioritise protein at each meal to help steady your blood sugar and support muscle, include iron rich foods like red meat, lentils and leafy greens, and remember that New Zealand soil is naturally low in iodine, so seafood, eggs and iodised salt matter more here than people realise for thyroid health. Gentle movement, particularly walking after meals and a bit of strength training each week, genuinely helps insulin sensitivity. Prioritising real, consistent sleep supports every single hormone system in your body, and managing stress matters more than most people realise, because chronically high cortisol can affect your thyroid function and your blood sugar regulation at the same time.

Bringing it all together

You are not imagining things, and you are not going mad. The symptoms you are feeling are real, they deserve to be properly investigated, and there is a good chance that once you understand exactly what is driving them, whether that is your changing hormones, your thyroid, your iron levels, your blood sugar, or a mix of everything, you will finally have a proper starting point to actually feel better.

Please do not settle for being told it is just menopause and to push through. Ask the questions, request the tests, and know that support really is available.

Sending you so much love as you navigate this stage of life. You do not have to figure it out alone, if you'd like some support reach out to me here

Warmly,

Kerry x

References

1.   Mintziori G, Veneti S, Poppe K, Goulis DG, Armeni E, Erel CT, Fistonić I, Hillard T, Hirschberg AL, Meczekalski B, Mendoza N, Mueck AO, Simoncini T, Stute P, van Dijken D, Rees M, Duntas L, Lambrinoudaki I. EMAS position statement: Thyroid disease and menopause. Maturitas, 2024. https://www.sciencedirect.com/science/article/abs/pii/S0378512224000860

2.   Harlow SD, et al. Abnormal uterine bleeding is associated with fatigue during the menopause transition. Menopause, 2025. https://vajenda.substack.com/p/new-research-on-fatigue-and-heavy

3.   Centers for Disease Control and Prevention, National Center for Health Statistics. Anemia Prevalence: United States, August 2021, August 2023. NCHS Data Brief No. 519, December 2024. https://www.cdc.gov/nchs/products/databriefs/db519.htm

4.   Badenhorst CE, Forsyth AK, Govus AD. A contemporary understanding of iron metabolism in active premenopausal females. Frontiers in Sports and Active Living, 2022. https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2022.903937/full

5.   Athar F, Gregory S, Houston EJ, Templeman NM. Insulin levels early in perimenopause inform vasomotor symptom incidence across the menopausal transition. Journal of Clinical Endocrinology and Metabolism, 2025. https://academic.oup.com/jcem/advance-article/doi/10.1210/clinem/dgaf699/8413273

6.   El Khoudary SR, Greendale G, Crawford SL, Avis NE, Brooks MM, Thurston RC, Karvonen-Gutierrez C, Waetjen LE, Matthews K. The menopause transition and women's health at midlife: a progress report from the Study of Women's Health Across the Nation (SWAN). Menopause, 2019. https://pmc.ncbi.nlm.nih.gov/articles/PMC6784846/