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Coffee: The science behind the health claims

Barista making espresso
Coffee contains a complex mix of molecules, including caffeine, antioxidants, and carcinogenic substances.

News proclaiming the health benefits of coffee is aplenty. The claims are bold: coffee can prevent anything from liver disease and cancer, to dementia and multiple sclerosis. On top of that, it is said to help us live longer.

Despite this, there are also more cautious studies. These tend to report on the risks of consuming caffeine, especially in children and young people, pregnant and lactating mothers, and individuals with underlying health conditions.

As you are sipping your first or your umpteenth cup of the day, find out what the latest research says about the safety of coffee and what coffee does to our bodies to cause the health miracles that everyone is talking about.

How much caffeine are we consuming?

Caffeine occurs naturally in tea leaves, coffee beans, and cocoa beans. Synthetic caffeine is also added to other drinks, some food products, and certain medications.

The levels of caffeine in coffee depend on the type of coffee used and how it was prepared. An average 8-ounce cup of brewed coffee contains between 95 and 165 milligrams of caffeine, while a single shot of espresso contains between 47 and 64 milligrams.

In the United States, 89 percent of adults consume caffeine - mostly in the form of coffee, tea, and, to a lesser extent, soft drinks. Men consume slightly more caffeine (on average, 240 milligrams per day) than women (who drink, on average, 183 milligrams per day).

Energy drinks make up only a small proportion of the caffeine intake of adults, but consumption did increase significantly between 2001 and 2010.

The majority of U.S. children (79 percent) also consume caffeine, with older children consuming more than younger ones.

Children below the age of 12 tended to consume caffeine in the form of tea, soda, and flavored dairy products, while older children mostly consumed coffee.

What happens inside our bodies?

Coffee contains a remarkably complex collection of molecules. Chief among them is, of course, caffeine, the central nervous system (CNS) stimulant that helps many of us to wake up in the morning and get through our day.

But there are also other antioxidant substances that help to mop up free radicals in our cells and activate DNA repair, as well as anti-mutagen molecules that stop cancer-causing DNA mutations from occurring. However, it's not all good news: coffee also contains carcinogens.

So what happens to the caffeine? Caffeine spreads throughout the body after it is taken up in the intestine. It takes quite a long time to be metabolized, which means that it is present in our bodies for some time after we consume it.

How we metabolize caffeine depends on our age. The half-life - that is, the amount of time taken to break down half the caffeine in our system - in adults is estimated to be between 3 and 7 hours.

But in newborns this is much higher, with numbers cited to be in the range of 65 to 130 hours.

Genetic variations make some people more susceptible to the effects of caffeine, by affecting both how quickly it is broken down and by how strong an effect it has on organs. Other things also affect caffeine metabolism.

The enzymes that break...

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