During the period I wrote about in the cortisol article and the liver function piece, my sleep was terrible.
Not the "I can't fall asleep" kind. The other kind. The 2am waking. Eyes open, brain wired, body exhausted. I'd lie there for an hour, sometimes two, running through tomorrow's to-do list with a clarity I never had during the day. Eventually I'd fall back asleep around 4am and wake at 6:30 feeling like I hadn't slept at all.
I assumed it was stress. My GP agreed that stress was probably part of it. But she also ran blood work, and three things came back that she said were worth addressing: my ferritin was on the lower end, my vitamin D was below optimal, and my HbA1c, while still normal, was sitting at the upper end of the healthy range. She told me that each of these can independently affect sleep quality, and that fixing the fixable things might help even if stress was the primary driver.
She was right. After supplementing iron and vitamin D and cleaning up my diet (which brought my HbA1c back toward the middle of the range), my sleep improved. Not perfectly. I still have bad nights when work is heavy. But the 2am pattern stopped.
I'm telling you this because the sleep conversation in Australia is dominated by two things: sleep hygiene advice ("put your phone down, keep your room dark, no caffeine after 2pm") and the sleep product industry (mattresses, weighted blankets, supplements, apps). Both have their place. But neither addresses the possibility that your sleep problem has a metabolic or hormonal component that a blood test could identify.
This article covers the blood markers most commonly linked to sleep disruption, who should consider testing, and how to tell the difference between a sleep problem that needs a blood test and one that needs a different approach.
A note before we get into it
General information only. I'm not a sleep specialist. Sleep disorders are complex and can have multiple contributing factors: physiological, psychological, behavioural, and environmental. If you have persistent insomnia, suspected sleep apnoea, or sleep problems affecting your daily function, see your GP. A sleep study may be appropriate.
Blood tests identify metabolic and hormonal contributors to sleep disruption. They don't diagnose primary sleep disorders.
Why sleep problems might be a blood test problem
Most people with sleep problems never consider that the cause might be in their blood. They adjust their bedtime routine, try melatonin, buy a new pillow. And for many, those interventions help, because the cause was genuinely behavioural or environmental.
But for some people, the problem is physiological. Their body is producing the wrong signals. Too much cortisol at night. Too little iron for restless legs. Blood sugar dropping at 2am. Thyroid running too fast or too slow. No amount of sleep hygiene will fix a hormonal or metabolic problem.
The clue is often in the pattern. Sleep hygiene problems tend to involve difficulty falling asleep (you're wired from screens, caffeine, or an irregular schedule). Metabolic and hormonal sleep problems often involve difficulty staying asleep, early waking, non-restorative sleep, or the "tired but wired" pattern where you're exhausted during the day but alert at night.
If you've optimised your sleep environment and habits and you're still not sleeping well, blood work is worth considering.
The blood markers that affect sleep
Thyroid function
How it connects to sleep
Both hypothyroidism and hyperthyroidism can disrupt sleep, through different mechanisms.
Hypothyroidism (underactive) causes fatigue and excessive sleepiness, but paradoxically, sleep quality is often poor. Non-restorative, with frequent waking. Hyperthyroidism (overactive) causes insomnia, anxiety, rapid heart rate, and difficulty falling or staying asleep.
The subtlety
Subclinical thyroid dysfunction (mildly abnormal but not dramatically so) can affect sleep quality without producing obvious waking symptoms. If your sleep disruption coincides with other thyroid-adjacent symptoms like fatigue, weight changes, temperature sensitivity, or mood shifts, thyroid is worth checking.
Detailed coverage: Thyroid Function Tests
Test it: Thyroid Function Test (TFT)
Iron and ferritin
How it connects to sleep
Iron deficiency is one of the most common identifiable causes of restless legs syndrome (RLS), the irresistible urge to move your legs, especially at rest and in the evening. RLS is a significant disruptor of sleep onset and maintenance.
The threshold is specific: ferritin below 50-75 µg/L has been associated with RLS in clinical studies. This is well above the standard lab lower limit of 15 µg/L, meaning you can have "normal" iron levels by lab reference ranges and still have iron-related sleep disruption.
Beyond restless legs
Iron deficiency can also contribute to general sleep disruption through its effects on dopamine metabolism and neurotransmitter regulation.
Detailed coverage: Iron and Ferritin Blood Tests
Test it: Iron Studies (Including Ferritin)
Blood sugar regulation
The 2am wake-up mechanism
This is the one nobody talks about.
When blood sugar drops during the night (reactive or nocturnal hypoglycaemia), your body releases adrenaline and cortisol to mobilise glucose from liver stores. These stress hormones wake you up, often with a racing heart, anxiety, or a sensation of alertness that feels disproportionate to the time of night.
If you consistently wake between 2am and 4am with your mind racing, blood sugar dysregulation is worth investigating. This pattern is especially relevant in people with insulin resistance, pre-diabetes, or poor blood sugar regulation, even if daytime glucose looks fine.
What to test
HbA1c (your 3-month average), fasting glucose, and fasting insulin (which can detect insulin resistance earlier than glucose markers). See the HbA1c article and the weight gain article for detailed coverage.
Test it: HbA1c · Fasting Glucose · Fasting Insulin
Magnesium
How it connects to sleep
Magnesium is involved in neuromuscular relaxation, GABA receptor function (your brain's calming neurotransmitter), and melatonin production. Low magnesium is associated with insomnia, restless sleep, and muscle cramping at night.
The testing caveat
Serum magnesium (the standard blood test) only reflects about 1% of total body magnesium. The rest is in bones and cells. A normal serum level doesn't fully rule out tissue deficiency. However, a low serum level is clinically meaningful and warrants supplementation.
Worth knowing
Magnesium is depleted by stress, alcohol, caffeine, and intense exercise. All of which also disrupt sleep. The overlap isn't coincidental.
Test it: Magnesium Blood Test
Vitamin D
How it connects to sleep
Vitamin D receptors are present in brain regions that regulate sleep. Several studies have found associations between low vitamin D and poor sleep quality, short sleep duration, and daytime sleepiness. The mechanism isn't fully understood, but correcting deficiency has been shown to improve sleep quality in some individuals.
Australian relevance
One in four Australians is vitamin D deficient, and indoor workers, shift workers, and those in southern states are disproportionately affected. All groups that also report higher rates of sleep problems.
Detailed coverage: Vitamin D Testing
Test it: Vitamin D (25-OH)
Cortisol
How it connects to sleep
Cortisol follows a circadian rhythm: high in the morning, low at night. When this rhythm is disrupted (by chronic stress, shift work, or HPA axis dysfunction), cortisol can remain elevated in the evening, preventing your body from transitioning into sleep mode.
The "tired but wired" pattern, where you're exhausted during the day and alert and agitated at night, is a hallmark of cortisol rhythm disruption. A single morning blood cortisol test has limitations for assessing this (it can't map the full diurnal curve), but it contributes to the broader picture.
Detailed coverage: Cortisol Blood Test
Test it: Cortisol Blood Test
Testosterone
The feedback loop
The relationship between testosterone and sleep is bidirectional. Low testosterone is associated with poor sleep quality, sleep apnoea risk, and reduced slow-wave sleep. And poor sleep suppresses testosterone production, creating a cycle where each problem worsens the other.
This is most clinically relevant in men over 40 with both sleep complaints and symptoms suggestive of low testosterone (fatigue, reduced libido, mood changes, muscle loss).
Detailed coverage: Testosterone Testing for Men
Test it: Testosterone Free/Total + SHBG
When sleep problems are NOT a blood test issue
Blood tests are one piece of the sleep puzzle. Many sleep problems have causes that blood work can't detect.
Sleep apnoea. The most under-diagnosed sleep disorder in Australia. Characterised by breathing interruptions during sleep, leading to fragmented sleep and daytime fatigue. Diagnosed by sleep study, not blood test. If you snore heavily, wake gasping, or have excessive daytime sleepiness despite adequate sleep duration, talk to your GP about a sleep study.
Behavioural insomnia. Irregular sleep schedules, excessive screen time before bed, caffeine timing, alcohol (which fragments sleep despite helping you fall asleep), and inadequate wind-down routines. These respond to cognitive behavioural therapy for insomnia (CBT-I), which is the gold-standard treatment for chronic insomnia.
Mental health conditions. Anxiety, depression, PTSD, and other conditions can profoundly disrupt sleep. If your sleep problems coincide with persistent mood changes, this warrants psychological or psychiatric assessment alongside (or instead of) blood work.
Shift work and jet lag. Circadian disruption from irregular schedules is a structural problem, not a blood test problem. Though blood markers like cortisol and thyroid can show downstream effects.
Medication side effects. Some medications (SSRIs, beta-blockers, corticosteroids, stimulants) can disrupt sleep. Review your medications with your GP if sleep problems coincide with starting or changing medication.
Who should be testing
Anyone with persistent sleep problems who has already addressed sleep hygiene and isn't seeing improvement. Blood work investigates the metabolic layer.
Anyone with the 2-4am waking pattern, especially if accompanied by a racing mind or anxiety. Blood sugar regulation is worth checking.
Anyone with restless legs or an irresistible urge to move at night. Ferritin should be checked.
Anyone with sleep problems plus other symptoms like fatigue, weight changes, mood changes, temperature sensitivity, or hair changes that might suggest thyroid dysfunction.
Shift workers. Chronic circadian disruption affects multiple metabolic markers. Regular testing provides baseline monitoring.
Men over 40 with sleep and energy complaints. The testosterone-sleep feedback loop is worth investigating.
How to prepare
Fast for 8-12 hours if including glucose and insulin markers.
Test in the morning. Cortisol, testosterone, and glucose are all most interpretable from a morning draw.
Mention your sleep pattern to the pathology staff. If you've been awake since 2am, your cortisol may already be elevated. Context helps interpretation.
Continue medications unless told otherwise.
Stop biotin supplements 48-72 hours before (interferes with thyroid assays).
Tests to consider through Bloody Good
Sleep-focused blood panel
Thyroid Function Test (TFT) — sleep disruption from both hypo and hyper
Iron Studies (Including Ferritin) — restless legs, sleep quality
HbA1c — blood sugar regulation and nocturnal waking
Fasting Glucose — overnight glucose patterns
Magnesium Blood Test — neuromuscular relaxation and GABA
Vitamin D (25-OH) — associated with sleep quality
Extended context
Cortisol Blood Test — rhythm disruption
Testosterone Free/Total + SHBG — for men with combined sleep and energy complaints
Fasting Insulin — insulin resistance and nocturnal blood sugar drops
Full Blood Count (FBC) — baseline
Comprehensive coverage
The Bloody Good Test covers 100 biomarkers including all the markers above. If your sleep problems might have multiple contributing factors, or if you're not sure where to start, the comprehensive approach rules out everything in one draw.
What to do after testing
If thyroid is abnormal: Treatment (levothyroxine for hypothyroidism, specific management for hyperthyroidism) typically improves sleep within weeks to months of achieving hormonal balance. See your GP.
If ferritin is below 50 µg/L: Supplement iron with your GP's guidance. If restless legs are present, improvements often appear within 4-6 weeks of ferritin rising above 50-75 µg/L. Retest at 3 months.
If blood sugar markers suggest insulin resistance: Dietary and lifestyle changes targeting blood sugar regulation (balanced meals, reduced refined carbohydrates, regular activity, adequate protein) can reduce nocturnal waking. The improvement is often noticeable within weeks.
If magnesium is low: Supplement (magnesium glycinate or citrate in the evening is a common protocol). Many people report subjective sleep improvement within 1-2 weeks, though this is partly anecdotal. The clinical evidence is moderate.
If vitamin D is low: Supplement. Sleep improvement from vitamin D correction tends to be gradual. Expect weeks to months.
If cortisol pattern suggests rhythm disruption: Address the drivers. Stress management, consistent sleep-wake times, light exposure in the morning, reduced stimulation in the evening. This isn't a supplement fix. It's a lifestyle recalibration.
If everything's normal: Your sleep problem is likely behavioural, psychological, or related to a condition blood tests can't detect (like sleep apnoea). This is valuable information. It redirects your investigation. Consider CBT-I (evidence-based insomnia therapy) or ask your GP about a sleep study.
Explore more biomarkers
Browse the Bloody Good Biomarker Directory
General information only. This article is not medical advice and is not a substitute for care from a qualified health professional. If you have concerning symptoms or urgent health issues, seek medical attention promptly.