Sleep Disorders in Adults: Types, Causes, and Evidence-Based Treatments

Sleep is not simply the absence of wakefulness — it is a highly active, biologically essential process during which the brain consolidates memories, the body repairs tissue, and the immune system performs critical maintenance. When that process is persistently disrupted, the consequences extend far beyond feeling tired.

Approximately 50–70 million adults in the United States have a sleep disorder, according to the American Academy of Sleep Medicine.^[1] Yet the majority go undiagnosed, partly because many people normalize poor sleep as an inevitable part of modern life. Understanding the major categories of sleep disorders — and what evidence-based treatment looks like — is a first step toward better outcomes.

Insomnia: The Most Common Sleep Disorder

Insomnia is defined clinically as difficulty initiating or maintaining sleep, or waking too early — occurring at least three nights per week for at least three months — that causes significant daytime impairment.^[2] Chronic insomnia affects an estimated 10–15% of the adult population.

Contrary to popular belief, the primary driver of chronic insomnia is not stress alone — it is a state of hyperarousal: the brain and body remain in an elevated state of alertness even when sleep is needed. This is why simply trying harder to sleep often makes insomnia worse.

CBT-I: The Evidence-Based First Line

Cognitive Behavioral Therapy for Insomnia (CBT-I) is recommended as the first-line treatment for chronic insomnia by the American College of Physicians, the American Academy of Sleep Medicine, and the European Sleep Research Society.^[3] A meta-analysis of 87 randomized controlled trials found that CBT-I produces clinically meaningful improvements in sleep onset latency, wake time after sleep onset, and sleep efficiency — effects that are maintained at 6–12 month follow-up, unlike sleep medications, which lose efficacy over time.^[4]

CBT-I components include sleep restriction therapy (temporarily limiting time in bed to build sleep pressure), stimulus control (reestablishing the association between bed and sleepiness), sleep hygiene education, and cognitive restructuring to address dysfunctional beliefs about sleep.

Obstructive Sleep Apnea: The Most Underdiagnosed

Obstructive sleep apnea (OSA) occurs when the muscles of the upper airway collapse repeatedly during sleep, causing breathing to stop — often for 10 seconds or more — dozens to hundreds of times per night. The brain rouses the body enough to restore airway tone, usually without the person fully waking or remembering these episodes.

OSA affects an estimated 26% of adults aged 30–70 in the U.S., but fewer than 20% of those affected have been diagnosed.^[5] The consequences of untreated OSA include significantly elevated risk of hypertension, cardiovascular disease, type 2 diabetes, stroke, and motor vehicle accidents.

Continuous positive airway pressure (CPAP) therapy remains the most effective treatment for moderate-to-severe OSA, with robust evidence for reducing cardiovascular risk, improving daytime functioning, and lowering blood pressure. For mild OSA or those intolerant to CPAP, oral appliances and positional therapy show meaningful benefit in appropriate patients.^[7]

Restless Legs Syndrome and Periodic Limb Movement Disorder

Restless Legs Syndrome (RLS) is characterized by an irresistible urge to move the legs, typically accompanied by uncomfortable sensations — described as crawling, tingling, or burning — that worsen at rest and in the evening, and are partially relieved by movement. RLS affects approximately 5–10% of adults and is twice as common in women.^[8]

The underlying biology involves dopaminergic dysfunction and iron deficiency in the brain — which is why iron supplementation (in those with low ferritin levels) and dopaminergic medications are first-line treatments. Notably, many common medications — including antihistamines, antinausea drugs, and certain antidepressants — can worsen RLS symptoms.

Circadian Rhythm Disorders

Circadian rhythm sleep-wake disorders occur when an individual's internal biological clock is misaligned with their environment or desired sleep schedule. The most common include:

• Delayed Sleep Phase Syndrome (DSPS): The body clock is shifted significantly later — individuals cannot fall asleep until 2–6 AM and struggle to wake at conventional times. Most prevalent in adolescents and young adults.
• Shift Work Sleep Disorder: Affects approximately 10–38% of shift workers, who must sleep and wake at times misaligned with their circadian biology.
• Jet Lag Disorder: Temporary circadian misalignment following rapid travel across multiple time zones.

Light therapy — timed bright light exposure to shift the circadian clock — is the most evidence-based non-pharmacological intervention for circadian rhythm disorders. Low-dose melatonin, timed appropriately (not simply taken at bedtime), can also facilitate circadian realignment.^[9]

When to Seek Professional Evaluation

• You have difficulty falling or staying asleep at least 3 nights per week for more than 3 months
• You snore loudly, gasp or choke during sleep, or have been observed to stop breathing
• You experience excessive daytime sleepiness despite adequate time in bed
• You have uncomfortable leg sensations that disrupt your sleep
• Poor sleep is affecting your work, relationships, or safety (including driving)