You are in your early to mid-40s, tired all the time, your hair is getting thinner, you wake in the night and can’t get back to sleep, and your mood tips over faster than it used to. The answer comes quickly: it’s the menopause. That may be true. But in my coaching I see time and again that three things are behind exactly these symptoms at once: the hormonal shift of perimenopause, a thyroid that is slowing down, and empty iron stores. And these three make each other worse.
What really happens to your hormones in perimenopause
Perimenopause does not begin with falling oestrogen. It can start in your mid-30s while your cycle is still regular, and it is shaped by three changes: oestradiol fluctuates and at times even rises higher than before, progesterone falls because ovulation becomes weaker or doesn’t happen, and the feedback between the ovaries and the brain falls out of step.[1] In about a third of cycles there is an additional, out-of-phase rise in oestradiol in the second half of the cycle.[1]
This explains why early perimenopause shows up mainly in your cycle: shorter or irregular cycles, heavier bleeding, tender breasts, restless sleep before your period, irritability. Hot flushes and sweating, on the other hand, are typical of late perimenopause.[2] Because hormone levels swing from cycle to cycle, the UK NICE guideline recommends recognising perimenopause in women over 45 from their symptoms, not with a blood test.[3] An FSH level also says little about how close your last period is.[1]
What your thyroid does in this phase
Hashimoto’s is the most common cause of an underactive thyroid (hypothyroidism) and affects women about four times as often as men; worldwide it is found in around 7.5 per cent of adults.[4] Typical symptoms of an underactive thyroid are tiredness, low motivation, feeling cold, weight gain, constipation and dry skin.[5] Many of these are also perimenopause symptoms. Falling oestrogen can make your skin drier, because oestrogen keeps moisture in the skin through collagen and the oil glands.[18,20] It also acts on the gut: oestrogen and progesterone influence gut movement, pain perception and the gut barrier. That is why bloating, alternating bowel habits and IBS-type symptoms can appear for the first time or get worse in perimenopause.[19,20]
On top of that there is a measurement problem. TSH shows how your thyroid is being driven, not how much active T3 actually reaches your tissues. Much of your T3 is only made locally in the tissues, by the enzymes DIO1 and DIO2, and stress and inflammation slow this conversion down.[6] So a woman in perimenopause with poor sleep, high stress and a TSH of 3 may have considerably less T3 available than her results suggest. It works the other way too: your thyroid affects your cycle, and both an underactive and an overactive thyroid can cause menstrual irregularities.[7]
Why the transition empties your iron stores
As progesterone falls, the lining of the womb builds up more, and periods become longer and heavier. In the US SWAN study, just over a third of women in the transition reported heavy bleeding lasting three or more days at least three times, and over three quarters reported bleeding lasting ten days or longer at least three times.[8] Every one of these episodes costs iron.
Empty stores make you tired, often long before a full blood count shows anaemia: in a randomised trial of women with normal haemoglobin but a ferritin below 50 µg/l, iron reduced fatigue considerably more than placebo.[9] Women with hair loss have markedly lower ferritin levels, as a meta-analysis of 36 studies shows.[10]
The vicious circle: how perimenopause, thyroid and low iron fuel each other
| Link | What happens |
|---|---|
| Perimenopause → iron | Less progesterone, heavier and longer bleeding, the stores run down[1,8] |
| Iron → thyroid | The enzyme TPO, which the thyroid uses to make hormones, contains haem and needs iron; when iron is lacking, fT4 in particular falls and TSH can rise[11,21] |
| Thyroid → cycle | An underactive or overactive thyroid can cause menstrual irregularities[7] |
| Sleep and stress → thyroid | Sleep problems increase during the transition;[12] stress and inflammation slow the conversion of T4 into T3[6] |
What you end up with is a woman who is exhausted, and three results that each sit “within the normal range” on their own. That is why I never look at just one area.
Which symptom can point where
| Sign | Perimenopause | Thyroid | Iron deficiency |
|---|---|---|---|
| Shorter, irregular cycle, heavier bleeding | typical, early[1] | possible[7] | a consequence, not the cause |
| Hot flushes, night sweats | typical, late[2] | more likely with an overactive thyroid | no |
| Exhaustion despite sleep | via poor sleep[12] | typical[5] | typical[9] |
| Thinning hair | possible | possible | documented link[10] |
| Feeling cold | rare | typical[5] | possible |
| Dry skin | possible, falling oestrogen[18,20] | typical[5] | – |
| Bloating, constipation, IBS-type symptoms | possible, oestrogen and progesterone act on the gut[19,20] | constipation typical[5] | – |
| Disturbed sleep before your period | typical[1] | possible | rare |
Signs, not a diagnosis. A diagnosis is always made by your doctor.
The blood tests that bring clarity
| Test | Lab reference (example) | How to read it |
|---|---|---|
| Ferritin (with CRP) | approx. 10–150 µg/l | below 30 µg/l iron deficiency confirmed;[13] from 100 µg/l unlikely in otherwise healthy people (German guideline on fatigue, DEGAM; IMD Berlin laboratory)[14,22] |
| Transferrin saturation | 15–45% | my functional guide value 25–35% |
| TSH | 0.22–4.46 mIU/l | over 95% of people with a healthy thyroid are below 2.5;[15] my functional guide value below 1.5 |
| fT3, fT4 | 2.3–4.2 pg/ml (3.5–6.5 pmol/l) · 0.9–1.7 ng/dl (12–22 pmol/l) | fT3 above 3.0 pg/ml (4.6 pmol/l), fT4 1.1–1.4 ng/dl (14–18 pmol/l) |
| TPO and Tg antibodies | below 35 and 20 IU/ml respectively | take any raised level seriously[16] |
| Cycle hormones | depend on the cycle day | not for diagnosing perimenopause over 45;[3] in coaching only for specific questions, for example progesterone in the second half of the cycle |
Lab reference: typical example values; your lab’s range applies. Functional guide values: based on experience from functional medicine and my coaching, not official reference values.
Alongside this, keep a cycle diary for at least three months: cycle length, bleeding days, how heavy the bleeding is, sleep, mood. In perimenopause it often tells you more than any single blood result.
Patterns I often see in my coaching
| Pattern | Typical results | What may be behind it |
|---|---|---|
| Heavy bleeding, exhausted, thinning hair | ferritin below 50 µg/l, haemoglobin normal | iron deficiency caused by perimenopause |
| Tired, cold, “results normal” | TSH from 2.5 up to the lab limit, fT3 in the lower third, TPO antibodies raised | early Hashimoto’s thyroiditis, made worse by empty stores |
| Restless sleep before your period, irritable | shorter cycles, low progesterone in the second half of the cycle | early perimenopause |
| All of the above | borderline ferritin, TSH above 2.5, cycle changes | the vicious circle across all three areas |
Patterns are signs from my coaching experience, not diagnoses.
What you can do now
- Keep a cycle diary, for at least three months.
- Have all three areas tested together: ferritin with transferrin saturation and CRP, TSH, fT3, fT4 and antibodies.
- Collect your old results. Trends tell you more than a single value.
- Don’t take iron on a hunch. Test first; too much iron can do harm.[17]
- Only change medication after talking to your doctor, and that includes thyroid hormones.
Where to start
- My free self-check shows you whether your signs point more towards your thyroid, perimenopause or the stress axis. You’ll then receive the starter guide that matches your result.
- My book *The Invisible Decade * takes you through perimenopause step by step, from your cycle and sleep to skin, hair and gut.
- Your free clarity call: 20 to 30 minutes on Zoom. Together we look at where you stand and which next step suits you.
Frequently asked questions
Can you have perimenopause and Hashimoto’s at the same time?
Yes. Both are common in women and one does not rule out the other. Hashimoto’s affects women about four times as often as men.[4] Heavy bleeding during the transition also empties the iron stores that your thyroid needs to make hormones.[8,11]
Are hot flushes an early sign of perimenopause?
Usually not. Early perimenopause shows itself mainly through cycle changes, heavier bleeding and sleep problems before your period.[1] Hot flushes and sweating are typical of late perimenopause.[2]
What is a good ferritin level for women?
There is no official optimal value. According to expert consensus, a ferritin below 30 µg/l means iron deficiency.[13] I go by the decision limits of the German laboratory IMD Berlin: from 100 µg/l, iron deficiency is unlikely in otherwise healthy people, measured when CRP is low.[14,22]
Can iron deficiency affect your thyroid?
Yes. The enzyme TPO, which your thyroid needs to make hormones, contains haem and depends on iron.[11] When iron is lacking, fT4 in particular falls, and TSH can rise.[21]
Read on
- Ferritin in women
- Understanding your thyroid blood tests
- Always tired? These blood tests are worth checking
This article does not replace medical advice. Diagnoses are made by your doctor; changes to medication belong in medical hands.
Sources
- Prior JC, Hitchcock CL. The endocrinology of perimenopause: need for a paradigm shift. Front Biosci (Schol Ed) 2011;3:474–486. doi.org/10.2741/s166 · Review
- Harlow SD et al. Executive summary of the Stages of Reproductive Aging Workshop + 10: addressing the unfinished agenda of staging reproductive aging. J Clin Endocrinol Metab 2012;97:1159–1168. doi.org/10.1210/jc.2011-3362 · Consensus (STRAW+10)
- National Institute for Health and Care Excellence (NICE). Menopause: identification and management. NICE Guideline NG23, sections 1.1 and 1.3. nice.org.uk/guidance/ng23 · Guideline (UK)
- Hu X et al. Global prevalence and epidemiological trends of Hashimoto’s thyroiditis in adults: a systematic review and meta-analysis. Front Public Health 2022;10:1020709. doi.org/10.3389/fpubh.2022.1020709 · Meta-analysis
- Chaker L, Bianco AC, Jonklaas J, Peeters RP. Hypothyroidism. Lancet 2017;390:1550–1562. doi.org/10.1016/S0140-6736(17)30703-1 · Review
- Sabatino L et al. Deiodinases and the three types of thyroid hormone deiodination reactions. Endocrinol Metab (Seoul) 2021;36:952–964. doi.org/10.3803/EnM.2021.1198 · Review
- Krassas GE, Poppe K, Glinoer D. Thyroid function and human reproductive health. Endocr Rev 2010;31:702–755. doi.org/10.1210/er.2009-0041 · Review
- Paramsothy P et al. Bleeding patterns during the menopausal transition in the Study of Women’s Health Across the Nation (SWAN). BJOG 2014;121:1564–1573. doi.org/10.1111/1471-0528.12768 · Prospective cohort study (n = 1,320)
- Vaucher P et al. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ 2012;184:1247–1254. doi.org/10.1503/cmaj.110950 · RCT (n = 198)
- Treister-Goltzman Y, Yarza S, Peleg R. Iron deficiency and nonscarring alopecia in women: systematic review and meta-analysis. Skin Appendage Disord 2022;8:83–92. doi.org/10.1159/000519952 · Meta-analysis (36 studies, n = 10,029)
- Zimmermann MB, Köhrle J. The impact of iron and selenium deficiencies on iodine and thyroid metabolism. Thyroid 2002;12:867–878. doi.org/10.1089/105072502761016494 · Review
- Kravitz HM et al. Sleep disturbance during the menopausal transition in a multi-ethnic community sample of women (SWAN). Sleep 2008;31:979–990. · Longitudinal study (n = 3,045)
- Naveed K et al. Defining ferritin clinical decision limits to improve diagnosis and treatment of iron deficiency: a modified Delphi study. Int J Lab Hematol 2023;45:377–386. doi.org/10.1111/ijlh.14016 · Delphi expert consensus
- DEGAM: S3-Leitlinie Müdigkeit [S3 guideline: Fatigue]. AWMF reg. no. 053-002, version 2023-01, long version (recommendation 5.3.1; sections 4.2.1, 4.2.5, 4.2.6). register.awmf.org · Guideline (Germany)
- Wartofsky L, Dickey RA. The evidence for a narrower thyrotropin reference range is compelling. J Clin Endocrinol Metab 2005;90:5483–5488. doi.org/10.1210/jc.2005-0455 · Review
- Vanderpump MP et al. The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey. Clin Endocrinol 1995;43:55–68. doi.org/10.1111/j.1365-2265.1995.tb01894.x · Cohort study
- Trost LB, Bergfeld WF, Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol 2006;54:824–844. doi.org/10.1016/j.jaad.2005.11.1104 · Review
- Thornton MJ. Estrogens and aging skin. Dermatoendocrinol 2013;5:264–270. doi.org/10.4161/derm.23872 · Review
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- Garofalo V et al. Relationship between iron deficiency and thyroid function: a systematic review and meta-analysis. Nutrients 2023;15:4790. doi.org/10.3390/nu15224790 · Meta-analysis (10 cross-sectional studies)
- IMD Institut für Medizinische Diagnostik Berlin-Potsdam. Ferritin bei Eisenmangel und Eisenmangelanämie: Neue Entscheidungsgrenzen ermöglichen eine differenziertere Beurteilung [Ferritin in iron deficiency and iron deficiency anaemia: new decision limits allow a more differentiated assessment]. Diagnostik-Information Nr. 400, Version 1. imd-berlin.de · Laboratory information
