What Does Poor Sleep Actually Mean? 3 Types of Sleep Problems and Their Root Causes

"Poor sleep" is a common complaint, but few people stop to ask: poor in what way, exactly?

Some people lie down and toss for an hour or two before sleep arrives. Others fall asleep easily but wake at 3 a.m. staring at the ceiling until 5. Still others are up at 5 a.m., an hour earlier than planned, still tired but unable to drift back off.

These three scenarios look similar on the surface. Inside the body, the mechanisms are quite different. And because they differ, so do the approaches.

This article introduces the clinical framework for classifying poor sleep, what may be happening in the body for each type, and the main categories of causes worth considering. This is the opening piece in KORE's sleep content series; follow-up articles go deeper into each cause group.

Three Types of Poor Sleep, Clinically Defined

The DSM-5 (Diagnostic and Statistical Manual of Mental Disorders) and ICSD-3 (International Classification of Sleep Disorders) divide insomnia into three primary symptom groups based on when during the night the problem occurs:

1. Sleep-Onset Insomnia: You lie down but cannot fall asleep for more than 20–30 minutes. This is the type most people recognize.

2. Sleep-Maintenance Insomnia: You fall asleep but wake one or more times during the night. You may or may not be able to return to sleep.

3. Early Morning Awakening (Terminal Insomnia): You wake at least 30 minutes earlier than intended and cannot go back to sleep, even though you still feel tired.

A person can experience one, two, or all three simultaneously. But identifying which type dominates helps point toward the right underlying cause.

Type 1: Difficulty Falling Asleep

What is happening during this phase?

Sleep begins when the brain reduces excitatory activity and increases inhibition. Two central factors are GABA (the brain's primary inhibitory neurotransmitter) and melatonin (the hormone that signals darkness to the body).

When cortisol, the stress hormone, remains elevated into the evening, it directly competes with both. The result is a brain that cannot "switch off" even when the body is exhausted.

Micronutrients involved

Magnesium plays a dual role in this process. It acts as a natural GABA agonist, helping the nervous system shift into an inhibitory state, and as an NMDA receptor antagonist, reducing excessive glutamate-driven excitation.

A double-blind placebo-controlled trial in older adults (Abbasi et al., 2012, PMC3703169) found that 500 mg magnesium daily for 8 weeks reduced sleep-onset latency, raised serum melatonin, and lowered cortisol. A subsequent systematic review and meta-analysis (PMC8053283) confirmed that magnesium shortened sleep-onset time by an average of 17.36 minutes compared to placebo.

Vitamin D is also implicated, indirectly, through its role in regulating serotonin, a precursor to melatonin. Prolonged vitamin D deficiency may disrupt the sleep-wake cycle downstream.

Rule out external factors first

Before considering micronutrients or hormones, screen for environmental contributors: screen light before bed (suppresses endogenous melatonin), a bright sleeping environment, noise, room temperature above 20°C, or caffeine consumed after 2 p.m.

Type 2: Waking During the Night

This is the most complex type because the likely cause varies significantly depending on what time the waking occurs.

What does the timing suggest?

Waking around midnight or 1 a.m.: Early night is when deep sleep (NREM stage 3) is most concentrated. Waking at this hour often involves muscle cramps, restless legs, or pain. Magnesium and calcium deficiency may contribute to involuntary muscle contractions during this phase.

Waking between 2 and 4 a.m.: This is the most complex window. Several mechanisms may be operating simultaneously:

• Cortisol begins to rise: Cortisol follows a circadian rhythm that starts climbing around 2–3 a.m. in preparation for morning awakening (PMC8813037). In individuals with an overactive HPA (hypothalamic-pituitary-adrenal) axis, cortisol may rise high enough to activate the sympathetic nervous system and trigger early waking.
• Low blood glucose: In people who eat a light dinner or have unstable insulin sensitivity, blood glucose may fall overnight. The body responds by releasing adrenaline as a protective mechanism, which can cause waking.
• Restless Legs Syndrome (RLS): A common but frequently unrecognized cause. Iron deficiency reduces the activity of tyrosine hydroxylase, the enzyme required for dopamine synthesis. Disrupted dopamine signaling in the midbrain leads to an uncontrollable urge to move the legs, typically worse at night when lying still. Research consistently identifies brain iron deficiency in the substantia nigra and thalamus as the most robust finding in RLS patients (Allen et al., 2013, PMC4608891; Earley et al., 2019, PMC6183309).

Waking between 4 and 6 a.m.: This phase is sometimes confused with type 3 (early morning awakening), but the mechanism is similar: cortisol is near its circadian peak. In those with an abnormal cortisol awakening response, the threshold for waking is markedly lower during this window.

The ability to return to sleep

This depends on the level of arousal at the moment of waking. If cortisol has not risen significantly and the waking was incidental, most people can return to sleep within 15–20 minutes. If the mind activates, worry sets in, or cortisol is already elevated, the ability to return to sleep drops sharply.

Type 3: Early Morning Awakening

The Cortisol Awakening Response and circadian rhythm

The Cortisol Awakening Response (CAR) is the natural increase of 38–75% in cortisol within 30–45 minutes of waking, which helps the body mobilize for the day (Endocrine Reviews, 2024). This is a normal component of the circadian rhythm.

In individuals with HPA axis dysregulation, however, CAR can occur earlier than expected, pulling waking forward with it. Those with chronically elevated evening cortisol tend to have a lower arousal threshold throughout the night, particularly during the rising phase of the cortisol curve.

Mood and hormonal links

Early morning awakening is a diagnostic criterion for major depressive disorder in the DSM-5. This does not mean everyone who wakes early is depressed, but when the symptom accompanies low mood, loss of interest, or a heavy feeling on waking, it warrants further evaluation.

In perimenopausal and menopausal women, declining estrogen and progesterone reduce slow-wave sleep quality and increase the frequency of nocturnal and early-morning awakenings. Progesterone has a mild sedative effect through GABA-A receptors; as levels fall, that effect is lost.

Internal vs. external causes: distinguishing before concluding

A key principle: before attributing poor sleep to micronutrients or hormones, rule out external factors with direct impact on sleep.

External (environmental):

• Noise: low-level but irregular noise (car horns, a barking dog, a restless child) activates the sympathetic nervous system even without full waking, reducing slow-wave sleep quality.
• Nighttime light: even dim light filtering through curtains can suppress melatonin.
• Room temperature too high: core body temperature must fall for deep sleep to occur; a hot room works against this.
• Drinks: caffeine, strong tea, or alcohol (alcohol accelerates sleep onset but disrupts sleep architecture in the second half of the night).

Internal (within the body):

• Micronutrient deficiency: magnesium, iron, vitamin D, and zinc each play roles in neural regulation and the sleep-wake cycle.
• Hormonal disruption: chronically elevated cortisol, age-related melatonin decline, estrogen/progesterone imbalance.
• Psychological factors: chronic anxiety keeps cortisol and norepinephrine elevated at night; depression alters sleep architecture.
• Underlying conditions: sleep apnea, chronic pain, irritable bowel syndrome.

Summary: Name it first, then look for causes

This table is not a diagnostic tool. Causes often overlap, and accurate identification requires evaluation by a qualified clinician.

What comes next in this series

This article is the introduction. Upcoming KORE content will go deeper into each area:

• Magnesium and sleep: mechanism, which forms absorb best, practical dosing
• Iron, dopamine, and nighttime restless legs
• Chronic cortisol: when the body cannot switch off at night
• Female hormones and sleep: perimenopause and menopause

To read more about a specific area, see magnesium and sleep or sleep phases and the role of micronutrients.

Content is educational and not a substitute for medical advice. Consult a professional before changing your supplement regimen.

References:

• Abbasi B. et al. (2012). The effect of magnesium supplementation on primary insomnia in elderly. Journal of Research in Medical Sciences. PMC3703169
• Mah J. & Pitre T. (2021). Oral magnesium supplementation for insomnia in older adults: a Systematic Review & Meta-Analysis. BMC Complementary Medicine. PMC8053283
• Peuhkuri K. et al. (2025). The Mechanisms of Magnesium in Sleep Disorders. Nature and Science of Sleep. PMC12535714
• Ranjbaran Z. et al. (2019). Sleep and Circadian Regulation of Cortisol: A Short Review. Frontiers in Endocrinology. PMC8813037
• Allen R.P. et al. (2013). Sleep disorders: A review of the interface between restless legs syndrome and iron metabolism. Sleep Medicine Reviews. PMC4608891
• Earley C.J. et al. (2019). Iron in Restless Legs Syndrome. Annals of Neurology. PMC6183309
• St-Onge M.P. et al. (2025). Micronutrients and midnight: the diet–sleep link. SLEEP. PMC12351264
• Gao Q. et al. (2019). The Association between Vitamin D Deficiency and Sleep Disorders. Nutrients. PMC6683772