Fatigue & Your Hormones: Why You're Always Tired

Fatigue is one of the most common symptoms women bring to my practice — and also one of the most frustrating. Not the tiredness that comes from a late night or a busy week. This is a bone-deep, persistent exhaustion that doesn't lift with sleep, that makes every day feel like wading through treacle, that has people wondering if something is seriously wrong.

Here's what I want you to know: this kind of fatigue is almost never "just stress" or "just getting older." In women, persistent fatigue has identifiable hormonal and nutritional drivers the vast majority of the time. The problem is that conventional medicine rarely tests for them comprehensively — and when it does, it often uses reference ranges that are far too wide to catch what's truly going on.

This article walks through the primary hormonal and nutritional drivers of fatigue in women, what to test for, and where to start addressing it.

Hormonal Fatigue vs. Regular Tiredness

Regular tiredness is contextual — it has an obvious cause (poor sleep, high workload, emotional stress) and it resolves when the cause resolves. You sleep well for a few nights, you take a break, and you feel better. Hormonal fatigue is different.

Hormonal fatigue tends to be persistent, disproportionate to your sleep or activity level, and often comes with a constellation of other symptoms — brain fog, low mood, difficulty concentrating, disrupted sleep despite tiredness, cold hands and feet, low libido, or changes in your menstrual cycle. It often worsens at predictable times: in the premenstrual week, during perimenopause, after childbirth, or during periods of high stress.

The distinction matters because the approach is entirely different. If you're hormonally fatigued, sleeping more won't fix it — but addressing the underlying hormonal driver can be genuinely transformative.

The Thyroid Factor

The thyroid is perhaps the most important single driver of energy in the body. Thyroid hormones regulate the metabolic rate of every cell — they are the body's "gas pedal." When thyroid function is low, every system slows down: metabolism, heart rate, digestive motility, brain function, and energy production at the cellular level.

Hypothyroidism — underactive thyroid — is the most common hormonal cause of fatigue in women. And yet it is routinely missed because standard testing measures only TSH (thyroid-stimulating hormone), which tells you what the brain is requesting from the thyroid but doesn't tell you how much active thyroid hormone (T3) is actually reaching your cells.

What a complete thyroid assessment looks like

A thorough thyroid panel includes TSH, Free T4, Free T3, Reverse T3, anti-TPO antibodies, and anti-thyroglobulin antibodies. Many women have what's called "subclinical hypothyroidism" — a TSH that sits in the upper range of "normal" but below the threshold for a clinical diagnosis — and experience very real fatigue, hair loss, cold intolerance, and brain fog that resolve when thyroid function is optimised.

Hashimoto's thyroiditis — the autoimmune form of hypothyroidism — is also extremely common in women and can cause significant fatigue even before TSH becomes abnormal. Testing for thyroid antibodies is essential and is rarely done as standard.

Cortisol & HPA Axis Dysregulation

The HPA (hypothalamic-pituitary-adrenal) axis is the body's primary stress response system. Under normal circumstances, cortisol follows a diurnal pattern: high in the morning (helping you wake and mobilise energy) and gradually declining through the day to allow sleep at night. When you're under chronic stress — physical, psychological, or physiological — this pattern becomes dysregulated.

High cortisol vs. low cortisol fatigue

In the early stages of chronic stress, cortisol is often elevated — leading to wired-but-tired energy, difficulty switching off, disrupted sleep, and afternoon energy crashes. Over time, if the demand is sustained, the HPA axis can become blunted — producing lower total cortisol output. This presents as profound, unrelenting fatigue, difficulty getting out of bed, low resilience to stress, and craving for salt and sugar. This is sometimes referred to colloquially as "adrenal fatigue," though the more accurate term is HPA axis dysregulation.

Cortisol also directly suppresses thyroid function and sex hormone production — so HPA dysregulation creates a cascade of hormonal disruption that amplifies fatigue through multiple pathways simultaneously.

Iron Deficiency: The Overlooked Culprit

Iron deficiency is the most common nutritional deficiency worldwide, and women are disproportionately affected — particularly those with heavy periods, those who are pregnant or postpartum, and those eating predominantly plant-based diets. Yet it is routinely missed because doctors typically check haemoglobin levels (which fall only with severe, established anaemia) rather than ferritin (stored iron), which depletes long before anaemia develops.

Iron is essential for the production of haemoglobin — the molecule in red blood cells that carries oxygen to every tissue in the body, including the brain and muscles. When iron stores are depleted, cells are literally receiving less oxygen and producing less energy. The result is fatigue, poor exercise tolerance, brain fog, and difficulty concentrating that can be profound.

The ferritin threshold question

Many labs report ferritin as "normal" at levels as low as 12–15 ng/mL, but optimal ferritin for energy, hair growth, and thyroid function is generally considered to be above 70–80 ng/mL. Always request the actual ferritin number rather than accepting a "normal" without knowing the value.

Blood Sugar & Energy Crashes

Blood sugar dysregulation is one of the most immediately correctable causes of fatigue — and one of the most consistently overlooked. The brain is the most glucose-hungry organ in the body, requiring a steady supply to function optimally. When blood sugar is unstable — spiking after high-carbohydrate meals then crashing as insulin overcompensates — the result is a predictable pattern of post-meal energy slumps, afternoon crashes, difficulty concentrating, and irritability.

This pattern is self-reinforcing: blood sugar crashes trigger cortisol release (to mobilise glucose from storage), which disrupts sleep, drives carbohydrate cravings, and sustains the cycle. Many women describe their fatigue as being worst in the early afternoon — a reliable signature of reactive hypoglycaemia rather than a disease process.

The fix is relatively simple: anchor each meal with protein and fat, reduce refined carbohydrates and sugar, eat regularly (every 3–4 hours if needed), and don't skip breakfast. Many women experience a dramatic improvement in sustained energy within days of stabilising blood sugar.

Low Progesterone & Sleep Quality

Progesterone has a direct sedating effect on the brain through its conversion to allopregnanolone, a neurosteroid that modulates GABA receptors — the brain's primary calming, inhibitory system. This is why adequate progesterone in the luteal phase supports deep, restorative sleep.

When progesterone is low — as it commonly is in women with anovulatory cycles, during the premenstrual week, or in perimenopause — sleep quality suffers. Women often report waking between 2 and 4 a.m. with a racing mind, or feeling unrefreshed despite sleeping for eight hours. This poor sleep quality then compounds fatigue throughout the day, even when the underlying hormonal cause isn't recognised.

Key Nutrient Deficiencies

Beyond iron, several other nutrient deficiencies are common in women and significantly contribute to fatigue:

Vitamin D

Vitamin D deficiency is epidemic in modern populations, particularly those living at higher latitudes, working indoors, or routinely using high-SPF sun protection. Vitamin D receptors are present in virtually every tissue, including the brain and mitochondria — the energy-producing organelles in cells. Low vitamin D is associated with fatigue, low mood, and impaired immune function. Test your level and aim to optimise to 60–80 ng/mL.

Vitamin B12

B12 is essential for red blood cell production, nerve function, and energy metabolism. Deficiency causes fatigue, brain fog, neurological symptoms, and megaloblastic anaemia. Women on plant-based diets, those with digestive issues affecting absorption (low stomach acid, gut dysbiosis), and those who have been on the oral contraceptive pill long-term are at elevated risk.

Magnesium

Magnesium is involved in over 300 enzymatic reactions in the body, including energy production (ATP synthesis), muscle and nerve function, and sleep regulation. Deficiency — which is very common, given that modern soils are depleted and stress increases magnesium excretion — contributes to fatigue, muscle tension, poor sleep, anxiety, and period pain. Magnesium glycinate at 300–400 mg before bed is a gentle, well-absorbed form that also supports sleep quality.

What to Test For

Here is the comprehensive panel I recommend for investigating hormonal fatigue:

Thyroid

• •TSH, Free T3, Free T4, Reverse T3
• •Anti-TPO and anti-thyroglobulin antibodies (for Hashimoto's)

Iron and blood

• •Ferritin (the key number — request the actual value, not just "normal/abnormal")
• •Full blood count (CBC) — to identify iron deficiency anaemia
• •Serum iron and transferrin saturation

Nutrients

• •Vitamin D (25-OH vitamin D)
• •Vitamin B12
• •Folate
• •Magnesium (RBC magnesium is more accurate than serum)

Hormones

• •Estradiol and progesterone (timed to cycle day 21 or 7 days before expected period)
• •Cortisol — ideally a 4-point salivary or urinary cortisol to assess the diurnal pattern
• •DHEA-S
• •Fasting glucose and insulin (for blood sugar assessment)

Where to Start

If you've been living with persistent fatigue and haven't had a comprehensive workup, start with these steps:

• •Get tested: ask your doctor for ferritin, a full thyroid panel (not just TSH), vitamin D, B12, and fasting insulin. These are the highest-yield tests for identifying correctable drivers of fatigue.
• •Stabilise blood sugar: protein at every meal, reduced refined carbohydrates, no skipping breakfast. This is the single fastest way to improve daytime energy for most women.
• •Address sleep quality: not just duration — magnesium glycinate before bed, a cool dark room, consistent sleep timing, and reducing screen exposure in the evening.
• •Reduce the stress load genuinely: HPA axis dysregulation requires actual stress reduction, not just stress management on top of an overwhelming schedule. Adaptogenic herbs (ashwagandha, rhodiola) can support the HPA axis while systemic changes are made.
• •Work with a hormone-literate practitioner: if initial tests are "normal" but fatigue persists, seek someone who looks at optimal rather than just reference range values, who tests thoroughly, and who understands the interconnections between thyroid, iron, cortisol, and sex hormones.

Persistent fatigue is not normal, and it is not inevitable. When you find the driver — and in most women, there is a clear, correctable driver — restoring energy is absolutely possible.