One cup of coffee too many can become a caffeine overdose

Downing seven double espressos over the course of a few hours sent 17-year-old Jasmine Willis to the hospital with palpitations and breathing difficulties.

The student was helping at her family's sandwich shop in Durham, north-eastern England, when she drank the espressos to help her stay awake during her shift.

Though the coffee overload had helped energise her initially, it ended up making her heart beat faster than normal and gave her a fever.

Doctors diagnosed Jasmine as suffering from a caffeine overdose that sent her body into a mild state of shock.

So, exactly how much is too much?

Generally, caffeine intake that exceeds 450mg a day (equivalent to four cups of coffee) is considered excessive and likely to trigger an overdose. Dr Aisha Lateef, associate consultant at the Department of Medicine at the National University Hospital, explained that this depends on the type of beverage one consumes, among other contributing factors — such as one's gender, height, weight, age and smoking habits.

Ms Nehal Kamdar, a dietitan at Raffles Hospital, added: "Caffeine sensitivity differs from person to person. Some can have several cups of caffeine-containing beverages in an hour without any effect while others may be sensitive to as little as a single cup."

In Jasmine's case, the amount she drank was more than twice the recommended quantity, as one shot of double espresso contains about 150mg of caffeine.

Caffeine helps a person stay awake because it stimulates the body's nervous and cardiovascular systems, leading to increased attentiveness, decreased fatigue and an elevated mood.

But an over-reliance on caffeinated drinks for your daily boost of energy is likely to create a dependence, as regular, heavy use of caffeine leads to increased tolerance to its effects.

Caffeine also increases the production of stomach acids and can bring on psychiatric disturbances like sleep disorders and anxiety.

Dependence on that cuppa also means that going one day without it could lead to withdrawal symptoms in the form of drowsiness, anxiety, headaches, fatigue and irritability.

These end up taking a toll on your body over time, said Ms Kavita Sundaram, dietitian at the Department of Dietetics at Tan Tock Seng Hospital.

"An overdose of caffeine can interfere with much needed sleep. This, in turn, has an effect on your daytime functioning. You might suffer from symptoms such as mood swings, lack of concentration and poor performance at work," Ms Sundaram explained.

Dr Lateef added: "Any substance which has a stimulant effect on our nervous system can make you feel temporarily alert and energetic. Moderation is key when taking any substance that raises alertness."

Ms Sundaram suggests substituting caffeine with a good night's rest instead, to boost one's energy levels.

"Having adequate physical activity of at least 30 minutes of exercise three times a week has been shown to help keep energy levels up," she said. - TODAY/fa