Fatigue is one of the most commonly reported symptoms during the menopausal transition, affecting an estimated 90% of women at some point during perimenopause.[1] It often presents differently from ordinary tiredness: a deep, persistent exhaustion that does not resolve with a good night's sleep, a sense of running on a reduced energy budget regardless of how much rest you get.

Treating fatigue as a single symptom of menopause means potentially missing other treatable conditions that are common in this age group, particularly iron deficiency and thyroid disorders. Each has a distinct cause, a distinct clinical picture, and a distinct treatment.

The Causes Are Often Layered

In most perimenopausal women with significant fatigue, at least two contributing factors are present simultaneously. Identifying each one separately matters because the treatments do not overlap.

Sleep Deprivation

Sleep disturbance affects 39–47% of perimenopausal women and 35–60% of postmenopausal women, compared to 16–42% in premenopausal women.[1] The disruption comes from multiple sources: vasomotor events waking women at night, changes to sleep architecture that reduce deep and REM sleep, and the rising cortisol in early morning hours that shifts the body toward waking.

Chronic mild sleep deprivation does not feel acute. After weeks and months of fragmented sleep, impaired function becomes the new normal, and women lose the reference point of what well-rested feels like. This makes it harder to identify sleep as the primary problem, because there is no single night of bad sleep to point to.

The cognitive and physical symptoms of chronic sleep deprivation overlap substantially with other causes of fatigue: difficulty concentrating, slower processing, reduced motivation, physical heaviness. Testing whether sleep improvement resolves the fatigue requires treating the sleep first.

Iron Deficiency Anaemia

Perimenopause is characterised by irregular and often heavier menstrual bleeding before cycles eventually cease. Heavy menstrual bleeding affects up to one-third of women of reproductive age, and iron deficiency anaemia develops in 63.4% of women with heavy menstrual bleeding.[2]

Iron is essential for haemoglobin production. Without adequate iron, red blood cells cannot carry sufficient oxygen to tissues. The result is fatigue, weakness, reduced exercise tolerance, and often breathlessness with exertion. Some women also experience cold intolerance, restless legs, and difficulty concentrating.

Iron deficiency anaemia is underdiagnosed in perimenopausal women for a specific reason: the symptoms are attributed to menopause rather than prompting blood tests. A woman who is also having hot flashes, poor sleep, and mood changes is likely to have her fatigue attributed to these, without the clinician checking whether heavy periods have depleted her iron stores.

A full blood count and ferritin level will identify iron deficiency. Ferritin below 30 mcg/L in the context of fatigue is clinically significant even when haemoglobin is still within normal range. Treatment with oral iron supplementation typically improves fatigue within four to six weeks of achieving adequate levels.

Thyroid Disorders

Thyroid disorders are more common in women than men, and their incidence rises with age. The symptoms of hypothyroidism overlap almost completely with those of perimenopause: fatigue, weight gain, mood changes, cold intolerance, brain fog, and menstrual irregularity.[3]

A review of thyroid disorder frequency in peri- and postmenopausal women found significant associations between thyroid dysfunction and menopausal symptoms, and concluded that thyroid disorders can go undiagnosed when confused with menopause.[3]

This overlap means thyroid screening is warranted in any perimenopausal woman presenting with significant fatigue. A TSH (thyroid-stimulating hormone) test is the standard first-line screen and is inexpensive. If hypothyroidism is found and treated with thyroid hormone replacement, symptoms previously attributed to perimenopause often resolve substantially.

Direct Hormonal Effects

Separate from the sleep, iron, and thyroid drivers, estrogen and progesterone directly influence energy regulation. Estrogen supports mitochondrial function across the body, and declining estrogen may reduce cellular energy production independently of sleep quality or red blood cell status. Progesterone has sedating properties, and the erratic progesterone levels of perimenopause can contribute to both fatigue and poor sleep.

The clearest evidence for direct hormonal effects on energy comes from women who start HRT and report improved energy alongside improved sleep and vasomotor symptom control. Separating these effects in clinical trials is difficult, but consistent reporting of improved energy with HRT is unlikely to be entirely attributable to sleep improvement alone.

A Diagnostic Framework

Given that fatigue in perimenopause frequently has multiple contributors, the most productive clinical conversation is not "I'm tired because of menopause" but a structured investigation of which specific factors are present.

The following tests are straightforward and together cover the most common reversible contributors:

  • Full blood count and ferritin: identifies iron deficiency anaemia
  • TSH: screens for hypothyroidism
  • Vitamin D level: deficiency is common and contributes to fatigue and low mood
  • Fasting glucose or HbA1c: insulin resistance increases during the transition and can cause energy fluctuations
  • B12 and folate: deficiency causes fatigue and is more common in women over 45

None of these tests requires specialist referral. Any GP or primary care provider can order them. If all return normal, the remaining work is addressing sleep quality, building exercise capacity, and assessing whether hormonal treatment is appropriate.

Matching Treatment to Cause

The interventions with the most consistent evidence are specific to the identified cause.

For sleep deprivation, addressing the sleep rather than managing the fatigue downstream of it is the only reliable approach. This may mean treating vasomotor symptoms, using CBT-I for behavioural sleep problems, or both.

For iron deficiency, oral iron supplementation is first-line. Intravenous iron works more rapidly and avoids gastrointestinal side effects; it is increasingly used when oral iron is not tolerated or when the deficiency is severe.[2] Addressing the underlying heavy bleeding treats the problem at its source.

For hypothyroidism, thyroid hormone replacement (levothyroxine) restores normal thyroid function and resolves the associated fatigue, though this can take six to twelve weeks to fully manifest.

For the direct hormonal component, HRT is the most targeted intervention. For women who cannot or prefer not to use HRT, regular aerobic exercise has consistent evidence for improving energy levels and fatigue in postmenopausal women: partly through improving sleep quality, and partly through direct effects on mitochondrial function and cardiovascular capacity.

References

[1] Polo-Kantola, P. (2011). Sleep problems in midlife and beyond. Maturitas, 68(3), 224-232. See also: Menopause and Sleep Disorders. https://pmc.ncbi.nlm.nih.gov/articles/PMC9190958/

[2] Itriyeva, K. (2022). Management of iron deficiency anemia in patients with heavy menstrual bleeding. Current Medical Research and Opinion, 38(4). See also: Iron deficiency anemia in patients with heavy menstrual bleeding. https://pmc.ncbi.nlm.nih.gov/articles/PMC11869313/

[3] Zaib, S., et al. (2023). Frequency of thyroid disorder in pre- and postmenopausal women and its association with menopausal symptoms. Frontiers in Endocrinology. https://pmc.ncbi.nlm.nih.gov/articles/PMC10365143/