Coffee is one of the world's most widely consumed beverages. It contains caffeine, a stimulant that can temporarily increase alertness and reduce feelings of tiredness.

Caffeine and alertness

Caffeine acts on the central nervous system. Moderate amounts can help some people feel more awake, but sensitivity differs substantially between individuals.

Caffeine consumed late in the day can interfere with sleep. High intake can also contribute to symptoms such as nervousness, restlessness, a rapid heartbeat or digestive discomfort in susceptible people.

What health research shows

Observational research has found associations between moderate coffee consumption and some health outcomes, including lower rates of certain diseases in some populations. These associations do not prove that coffee itself prevents those diseases.

Coffee should therefore not be promoted as a treatment for diabetes, Parkinson's disease, liver cancer, respiratory disease or other medical conditions.

Filtered and unfiltered coffee

Preparation method can matter. Some compounds found in unfiltered coffee can raise blood cholesterol, while paper filtering removes much of these compounds.

Pregnancy and individual circumstances

People who are pregnant are commonly advised to limit caffeine intake. Anyone with a medical condition, troublesome symptoms or questions about medication interactions should seek advice appropriate to their circumstances.

Hot or cold?

Whether coffee is served hot or cold is largely a matter of preference. Added sugar, syrups and cream can substantially change the nutritional content of a coffee drink.

Coffee can be enjoyed as part of a balanced diet, but claims that it cures disease, prevents snoring or provides guaranteed health protection go beyond what the evidence supports.