What you eat and drink during the day can affect how quickly you fall asleep, how deeply you sleep and how you feel the next morning. In Part 4 of Sleep Science, we look at caffeine, alcohol and food.
Caffeine: the alertness booster
Caffeine is found in coffee, tea, energy drinks, many soft drinks and chocolate. It works mainly by blocking adenosine, the chemical that builds sleep pressure (see Part 1). That is why it helps you feel alert, but it can also make it harder to fall asleep.
How long caffeine lasts
Caffeine's half-life, the time it takes the body to clear half of it, is often cited as around five hours in healthy adults, but it can range from about two to ten hours depending on genetics, age, pregnancy, smoking and some medications. That means an afternoon coffee may still be affecting you at bedtime.
Practical tips
- Many sleep experts suggest avoiding caffeine for at least six hours before bed, or after early afternoon if you are sensitive.
- Remember hidden sources such as tea, cola, energy drinks, chocolate and some pain relievers.
- If you have trouble sleeping, try cutting back gradually to see if it helps; sudden stopping can cause headaches.
Alcohol: a misleading nightcap
Alcohol can make people feel sleepy and fall asleep faster. However, it disrupts sleep later in the night. As the body processes alcohol, sleep often becomes lighter and more broken, and REM sleep is reduced, especially in the first part of the night.
Alcohol can also relax throat muscles, which may worsen snoring and sleep apnoea (see Part 7), and it often leads to waking to use the bathroom.
Practical tips
- If you drink, avoid alcohol in the hours before bed.
- Drink water as well, and keep amounts within health guidelines.
- Do not use alcohol as a sleep aid.
Food and meal timing
Heavy or late meals
Large, rich or spicy meals close to bedtime can cause discomfort or heartburn, especially when lying down. Many experts suggest finishing large meals at least two to three hours before bed.
Going to bed hungry
On the other hand, hunger can also keep you awake. If you need something, a small, light snack such as yoghurt, a banana, a small bowl of cereal or a handful of nuts is usually better than a heavy meal.
Drinks before bed
Drinking a lot of fluid late in the evening may lead to night-time bathroom trips. Try to drink well during the day and reduce fluids in the last hour or two before bed.
Do any foods help sleep?
You may hear claims about warm milk, tart cherry juice, kiwi fruit or herbal teas such as chamomile. Some small studies suggest possible benefits, but evidence is limited and effects are modest. A calming, caffeine-free warm drink can be a pleasant part of a bedtime routine, even if it is not a cure.
Overall, a balanced diet with regular meal times is linked to better sleep than any single "sleep food."
Nicotine
Nicotine is a stimulant and can make it harder to fall asleep and stay asleep. Withdrawal during the night can also disturb sleep. Quitting smoking benefits sleep and overall health; health services can offer support.
Key takeaways
- Stop caffeine at least six hours before bed, earlier if sensitive.
- Avoid using alcohol as a sleep aid.
- Finish big meals two to three hours before bed; choose light snacks if hungry.
In Part 5, we look at screens, light and melatonin.
Sleep Science: the full series
- Part 1: How Sleep Works
- Part 2: How Much Sleep You Need
- Part 3: Better Sleep Habits
- Part 4: Caffeine, Alcohol and Food (you are here)
- Part 5: Screens, Light and Melatonin
- Part 6: Insomnia
- Part 7: Snoring and Sleep Apnoea
- Part 8: Naps, Shift Work and Jet Lag
This article is for general information only and is not medical advice. If you have ongoing sleep problems, loud snoring, breathing pauses or daytime sleepiness, please speak to a doctor.
