How much coffee is too much?

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Every caffeine fiend knows the feeling of going overboard. That sense that you’re teetering on the edge of disaster, but you’re not quite sure why. Or worse, heart palpitations.

Although you know it when you feel it, figuring out how many coffees are too many coffees in advance isn’t always that easy. So The Glow decided to enlist the help of two local health experts: Dr Ian Musgrave, a senior lecturer in the University of Adelaide’s pharmacology department; and Professor Chris Semsarian, a cardiologist from Sydney’s Royal Prince Alfred Hospital.

First, the good news: unless you’re throwing back a short black every two minutes, you’re very unlikely to ingest a lethal amount of caffeine in a day. “Generally, caffeine itself is not very toxic, so you’d have to drink something on the order of 130 or so cups of espresso in order to kill yourself from that,” says Dr Ian Musgrave. Even the most ardent coffee fan would admit that’s a little excessive.

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On an individual level, determining how much coffee is too much is tricky, as the body’s reaction to caffeine differs from one person to the next. While you may find a late afternoon latte keeps you up all night, your best friend might sleep soundly even after a 9pm coffee hit. Interestingly, a study of 120,000 people released last week indicates your coffee consumption is determined, in part, by your DNA; while a new book by Cambridge psychologist Brian Little suggests coffee affects the work performance of extroverts and introverts differently.

There are a number of variables that can determine how you respond to coffee. For instance, if you’re a regular coffee drinker, your body’s likely to accommodate and be more tolerant of caffeine than someone who is “coffee naive”, Dr Musgrave says. “If you’ve never had coffee before and you slam down, say, ten espressos in a row you’re going to have very exaggerated effects. You may even show signs of caffeine intoxication where you get the tremors, the heart palpitations.”

Similarly, some people have heart and liver conditions that impact how caffeine is metabolised. “If you are someone who has a mutant form of the enzyme that breaks down coffee in your body, or if you’ve got liver disease that damages your body’s ability to break down caffeine, or if you have some forms of heart disease, then you’ll be more likely to have the toxic effects of caffeine than the normal population,” Dr Musgrave explains.

Body size can also determine how your body responds to caffeine. "There are certainly differences in metabolism in people with different body weights. A 40kg woman is more likely to experience an impact from caffeine than a 100kg male," explains Professor Chris Semsarian.

Professor Semsarian also points out that there are recommended levels of daily caffeine intake. "For adults it’s 400mg of caffeine a day, for children and adolescents it’s 100mg a day. Exceeding those amounts can lead to very significant cardiac and neurological symptoms ... including palpitations, fast heart rates, high blood pressure and insomnia," he says. "Chronic use of caffeine can lead to irritable behaviour, higher blood pressure and things like that."

The amount of caffeine in dietary products varies; in coffee, it can depend on preparation methods (eg. whether it's steam-pressed or drip filtered) and the kind of bean used. "A can of Coke has 40-45mg; an instant coffee would have maybe 50mg, and a can of energy drink would have 80mg - these are ballpark figures," says Professor Semsarian. "So you’re talking about a range of anywhere between 6 and 8 coffees a day [to reach the 400mg recommendation]."

However, Dr Musgrave highlights there is a growing body of research suggesting regular, "modest" coffee consumption might offer some modest health benefits, although more research is needed. "If you’re drinking between 4 to 6 cups of coffee a day, over a long period of time ... it appears to lower your probability of dying overall," he says. "It appears to lower your probability of [type 2] diabetes, it appears to lower your probability of cardiovascular disorders, it may lower your probability of getting Parkinson’s disease."

Professor Semsarian cautions that coffee isn't the only source of caffeine in our diets. "It's not just coffee. People also access caffeine through No Doz - which has up to 200mg [of caffeine] in a tablet - caffeine strips and powdered caffeine," he says. "The scariest input is from energy drinks. Each has about 80mg of caffeine, but in addition has other stimulants like torine and guarana ... The overall effect of these drinks is caffeine times one hundred."

In summary, there isn't a definitive 'point of no return' when it comes to how much coffee you should be drinking per day. Just like most dietary decisions, it seems moderation - and trying to work out your personal limit - is the best approach.

"The bottom line is to enjoy your coffee, do so in moderation, but unless you have a heart or liver disease ... and your doctor says to cut down, modest coffee consumption should be fine," Dr Musgrave says.

How many coffees do you drink per day?