Caffeine, Food, Alcohol, Smoking and Sleep


How can caffeine affect my sleep?

Caffeine is a drug that acts as a stimulant, both mentally and physically. It is found in many drinks and foods that are common in our everyday life. These include tea, coffee, chocolate and cola drinks. Many people do not think of it as a drug. It can be bad for your sleep in three ways. Firstly it can make it harder to go to sleep. Secondly it can make you sleep more lightly and wake up more often during the night. Thirdly, it may make you have to get up to go to the toilet during the night.

Some people need more caffeine than others to have the same effect. As a rule, caffeine takes about 30-70 mins to reach peak levels in your body. Its effects can last from three to seven hours, but your body needs about 24 hours to completely eliminate it. Many people who consume a lot of caffeine think that it no longer stops them from being able to go to sleep, because they have become immune to this effect. However research shows that, even if they think otherwise, their sleep is impaired and they would sleep much better if they abstained from it.

How much caffeine is in common foods and drinks?

The amount of caffeine in a drink will vary with its strength. The table below shows the amount of caffeine in the most common sources. Note that normal tea has a lot more caffeine than many people think.

SUBSTANCE Caffeine Content (Milligrams)
Coffee (250ml or 1 small to average sized cup)
Instant coffee
Brewed coffee
Iced Coffee
Decaffeinated coffee
Depends on brand and strength
65-100 mg 
Up to 150mg per carton 
Tea (250ml or 1 small to average sized cup)
Herbal tea
Green tea
Normal tea

0-30 mg
50-70 mg

Soft Drinks (375ml can or medium sized cup)
Coca-Cola, Pepsi or similar               
Red Bull (250ml)


50 mg
80 mg
80 mg
150 mg
Most Chocolate Bars (Dark chocolate has more caffeine)
Cocoa and Hot Chocolate

20 - 60 mg per 200 mg serve
10 - 70 mg per cup
Caffeine Tablets
NoDoz (Regular strength, per tablet) 


How much caffeine should I have?

If you are having trouble sleeping, you should try to limit the amount of caffeine that you have. It is best to have no more than 200mg per day. There are different views on how many hours before bed you should have your last caffeine intake. Some say caffeine should be avoided for at least 3 to 7 hours before going to sleep. Others say no caffeine after lulnch time if you have sleep problems. Many people will find that their sleep improves with just this change. But you should also keep in mind that caffeine is addictive. This means that if you stop suddenly, you may suffer from headaches, tiredness and anxiety. In this case, gradually cutting down may be better.

How can food affect my sleep?

Both what you eat in your meals and when you eat them can affect your sleep. As a rule, a healthy, balanced diet will be good for your overall health and well-being. You will have more energy during the day and sleep better at night. It is best if you allow 2-3 hours between having your last main meal of the day and going to bed. You should not go to bed hungry, nor just after you have had a meal. If you have a long time between dinner and bed, you may find that eating a small, light snack (e.g. a piece of fruit) or having a milk drink prior to going to bed helps you to sleep better. Some people find that rich or spicy foods in the evening make it more difficult to sleep well at night.

Will alcohol help my sleep?

Although alcohol will make you feel sleepy and may help you fall asleep at night, it actually disrupts your sleep later. In the second half of the night, sleep after drinking alcohol is associated with more frequent awakenings, night sweats, nightmares, headaches and is much less restful. It is best to avoid alcohol for at least 4 hours before bedtime. Binge drinking will affect your levels of melatonin for up to a week. Melatonin makes us feel sleepy at night, helps us to sleep better and regulates our body rhythm.

Will a cigarette help my sleep?

You may think that having a cigarette before bed or in the middle of the night relaxes you, but this is not the case. Nicotine is a stimulant and makes it harder to fall asleep and to stay asleep. Cigarettes should ideally be avoided altogether, and certainly for at least 2 hours before bed.

Further information: (short slide show)

Download a printable copy.