Sleep: what the research says, and where to start
How sleep works, what to read when it goes wrong, and what the evidence says about supplements. Each section points to the guides that go through the studies.
The short version
- Hours. The CDC lists 7 or more hours for adults aged 18 to 60, and NHLBI and the National Sleep Foundation panel give 7 to 9 hours. These are consensus recommendations, and they are ranges. See how much sleep adults need.
- How it works. Sleep runs in cycles of REM and non-REM stages, and two systems help time it: a need for sleep that builds while you are awake, and a body clock. See how sleep works.
- Chronic insomnia. The best-supported approach is cognitive behavioral therapy for insomnia (CBT-I). The American College of Physicians and the American Academy of Sleep Medicine both give it a strong recommendation. See waking up at night.
- Supplements. For the ten ingredients we looked at, the research shows small or inconsistent effects, or too few trials to say, depending on the ingredient. None of the ingredient guides says what to take. See the overview of sleep supplements.
Last reviewed September 20, 2026.
How sleep works
Seven guides on how sleep is regulated, how many hours adults are advised to get, and what light, temperature and cortisol have to do with it. Start with the sleep science overview.
When sleep goes wrong
The CDC says to talk to your healthcare provider if you regularly have problems sleeping. These guides go through what guidelines and research say about three common complaints.
- Why do I keep waking up at night?
- Waking often during the night is the most common insomnia symptom, according to NHLBI. It counts as chronic insomnia when it happens 3 or more nights a week for 3 months or longer. The best-supported approach for chronic insomnia is cognitive behavioral therapy for insomnia (CBT-I).
- Why do I wake up at 3 AM?
- We found no guideline or study that explains waking at 3 a.m. specifically. The guide goes through the usual causes of night waking and when to see a doctor.
- Why is my mind racing at night?
- Researchers describe this as cognitive-emotional hyperarousal, a part of hyperarousal in insomnia. The guide covers what the research says about worry, what a bedtime list does, and when to get help.
Supplements
A short summary of what the research says for each of ten sleep ingredients, with a link to the full guide on each, is in the overview of natural sleep supplements.
A product we review
Yu Sleep is a liquid sleep supplement. Our review, is it legit and side effects guides, like the other guides that mention it, contain affiliate links, which means we may earn a commission if you buy through them. The affiliate disclosure has the full terms, and how we review explains our method.
Before you rely on any of this
We are an editorial team, not doctors, and nothing here is medical advice. Each guide lists its sources, and the science, ingredient and sleep problem guides have a section on what is uncertain. If sleep trouble is persistent, or you have a medical condition or take any medication, talk to a healthcare provider.