Sleep

Short sleep makes good moods rarer and bad moods stronger. Improving sleep improves how you feel. For the how-to, go to sleepgood.now.

• Evidence: Strong
• Takes: 7 or more hours a night

Why it matters

After a short night, most people notice they’re more irritable. The research says the bigger change is on the other side: you get less enjoyment out of things. Combining 64 studies, losing sleep had a large effect on positive mood and a moderate effect on negative mood [1]. So a bad night doesn’t just make you grumpy. It makes the good parts of your day feel flatter.

The link also runs in the useful direction. A meta-analysis of 65 trials with over 8,600 people looked at what happened when an intervention improved sleep. Mental health improved by a medium amount, including stress and rumination (going over the same worries again and again). The more sleep improved, the more people’s mental health improved [2]. That dose-response pattern is a good sign that sleep is a cause, not just a side effect of feeling bad.

How to do it

These are the basics. sleepgood.now covers each one in depth.

1. Keep a steady wake-up time, including weekends, give or take a little. A fixed wake time is easier to control than a fixed bedtime, and the bedtime tends to follow.
2. Give yourself enough time in bed. US sleep experts recommend that adults sleep at least 7 hours a night, regularly [3]. Time in bed needs to be a bit longer than that. If you need an alarm every day and still wake up groggy, you probably need more.
3. Get light in the morning and dim light at night. Daylight soon after waking helps set your body clock. See Daylight and time outdoors.
4. Watch caffeine and alcohol. Caffeine in the afternoon and alcohol in the evening both make sleep lighter. See Alcohol and caffeine.
5. Have a wind-down routine. The same short routine before bed: dim lights, phone away, something calm.

Common mistakes

• Treating sleep as the first thing to cut. When you’re busy, an extra hour of work at night often costs more in mood and focus the next day.
• Catching up with long weekend lie-ins. Sleeping in by several hours shifts your body clock, which makes Sunday night and Monday morning harder.
• Lying in bed awake for a long time. If you can’t sleep, get up, do something quiet in dim light, and go back when you feel sleepy.
• Judging your mood after a bad night. If you slept badly, expect the day to feel flatter. Avoid big decisions or hard conversations if you can, and don’t read too much into how you feel.

Evidence

Rated Strong. Two large meta-analyses point the same way. The first combined lab studies that cut sleep on purpose [1]. Those are short experiments, but they show cause and effect clearly. The second combined randomized trials of ways to improve sleep and found matching improvements in mental health [2]. Many of those trials included people who were already struggling, so the effect for people who are generally fine may be smaller.

Topics: Sleep, Mood, Energy, Foundations

Sources checked 4 October 2026. Spot a mistake? Tell us.