As with most horror stories, this one unfolds at night.

On the eve of examinations or essay deadlines, many students often guzzle coffee or cans of energy drinks to stave off sleep and power through their studies. Some even concoct a more potent brew by mixing black coffee with energy drinks that contain caffeine for an extra jolt of alertness.

Qistina, a 21-year-old motion graphic designer who prefers to be known only by her middle name, recalls needing at least two large cups of local coffee to stay awake while studying at a polytechnic. It led her friend to ask if mixing energy drinks with coffee would be the next thing she would do.

"It was the first time I had heard of such a mix," Qistina says. "I don't think I would ever do it, but the idea has stuck with me since."

The cost of this desperate bid to stay awake is steep. As the artificial surge of energy wanes, students find themselves transformed into literal zombies, shambling through the following days in a sleep-deprived haze. Yet, this is a price they are willing to pay for academic success.

Some others crank things up a notch by mixing energy drinks with alcohol. When Dil Kaur was an undergraduate in Melbourne, one of her favourite drinks was vodka mixed with zero-calorie Monster. The 27-year-old stylist says it was a cheap way to get a quick buzz with her limited spending power as a student.

With her heart racing from the caffeine and alcohol coursing through her veins, she was set up for a great night out. Now, as a working adult, Kaur opts for Jagerbombs - a cocktail that combines Red Bull with Jagermeister, a herbal liqueur with 35 per cent alcohol.

"I like it because I come to drink after work, and I know I would get sleepy soon. This wakes me up," she says.

Media practitioner Aidan Razali, 24, observes that his peers and other young adults want to avoid getting drunk too quickly and embarrassing themselves in front of friends. They believe mixing energy drinks with alcohol helps them stay in that sweet spot of feeling "high" for a longer period without passing out.

The real haunting in these tales goes beyond young adults burning the midnight oil or chasing the next shot in a state of "wide awake drunk". It is the unsettling fact that they see no issues with their habit, even in the face of potential health risks.

Rachel Wong, a dietitian at National University Hospital (NUH), says mixing energy drinks with coffee increases the overall caffeine content. This heightens the risks of caffeine overdose, leading to symptoms such as increased heart rate and blood pressure, anxiety and jitteriness.

When energy drinks are mixed with alcohol, the stimulating effects can mask intoxication, potentially leading to more drinking and a higher risk of alcohol poisoning as well as related harms such as bodily injuries and impaired driving.

These combos can also cause sleep problems and digestive discomfort such as nausea, stomach pain and dehydration due to caffeine's diuretic effect, Wong says.

Qistina, despite the warnings, says: "I supposed as design students, and now designers, we have so many deadlines and quick turnarounds, it is more acceptable to keep consuming stimulants like these to stay awake."

Kaur adds: "I remember there was a warning that said 'do not mix with alcohol' on the can of zero-calorie Monster energy drink I used to mix with vodka. The caffeine was so high that I would probably get an immense hangover if I were to do the same thing now. But back then, I was young, so most of the time, I was like, it is okay."

How much is too much?

In January, Nominated Member of Parliament Jean See Jinli asked if the Ministry of Health would consider introducing measures to restrict the sale of high-caffeine beverages, including energy drinks, to young people.

Health Minister Ong Ye Kung, in his written parliamentary response, said Singapore's food regulations do not set maximum limits on caffeine added to beverages. Internationally, there is also no consensus on health-based guidelines or standards for caffeine permitted in food. As such, there is no definitive evidence to support a universal maximum threshold.

Enjoying coffee and tea has always been a pleasurable ritual in Singapore. In the past year alone, speciality coffee chains from China, Indonesia, Canada and Taiwan have opened shops in Singapore, joining an already bustling landscape of independent cafes and more than 60 bubble tea brands.

Experts predict that these non-alcoholic beverages will see the fastest growth over the next five years. A July 2022 survey, done by senior researcher R. Hirschmann of global data firm Statista, revealed that nearly 55 per cent of around 1,000 respondents in Singapore had purchased coffee in the past week, while 46.9 per cent had bought tea or bubble tea.

It is a surge that is partly driven by influencer marketing and product innovations tailored to Gen Zs. Caffeine consumption was once seen as a rite of passage for young adults transitioning from school to the "real world". While Gen Zs consume traditional kopi and teh, they are also looking out for drinks that match their dynamic lifestyles.

Consumption of energy drinks is also on the rise, with the market expected to reach 5.21 litres per person in 2024, according to Statista. Marketed for their ability to boost energy and focus, they appeal to Gen Zs who are constantly looking for quick, effective ways to power through their busy schedules.

Yulanda Heng, principal dietitian at KK Women's and Children's Hospital (KKH), says: "Caffeine can be found hidden in many common foods and drinks, including chocolates and vitamin water. It is a stimulant that increases activity in the brain and nervous system. In appropriate doses, it can make one feel more alert and focused."

According to local health portal HealthHub, it is best to keep caffeine consumption moderate, preferably no more than 400mg per day. That is not more than three cups of kopi from the neighbourhood coffee shop or hawker centre.

Most common caffeinated beverages in Singapore contain less than 150mg of caffeine per cup, making it unlikely for individuals to exceed the recommended daily limit.

Excessive caffeine intake - 600mg to 900mg and above - can lead to muscle tremors, insomnia, irregular heartbeat, increased blood pressure, headaches and acid reflux. Even smaller amounts can trigger these problems for individuals with lower caffeine tolerance.

But do Singaporeans, especially Gen Zs, know how much caffeine is in their favourite beverages? Do they care about the impact on their bodies?

Qistina says: "Back in school, I would have up to two cups of coffee and two cans of energy drink a day. I knew it was bad. My friends told me to cut down, but I couldn't. I needed them to function."

She is fortunately not a big fan of either now.

Aidan's parents were very strict about what he could drink as a child, and he only started drinking coffee when he was in polytechnic. "I would be drinking two or even three cups a day," he says, adding that the canteen auntie knew his order - kopi-o-peng (iced black coffee) - as soon as she saw him.

Even now, as a working adult, he keeps a bottle of black coffee from the supermarket in his car, sipping it as others might sip water.

Gladys Leong, 27, recalls she once drank six cups of coffee in a day. This happened the week before her honours thesis submission, when she pulled late nights in school to finish her work.

"I took a big metal cup to the canteen auntie and asked her to fill it with coffee. I saw her pour at least three to four cups into my metal cup, and I went back to the auntie again later, making it at least six cups in total.

"It was crazy. My heart was palpitating and I could feel it. I had to do breathing exercises to calm down. I think people really underestimate the effects of caffeine. We keep drinking it, thinking we need it, without realising how much we have already had. We just drink," says the entrepreneur who, among other business interests, owns an education consultancy.

KKH's Ms Heng says consuming a large amount of caffeine at once forces the body to handle a surge, temporarily making the person feel more awake and energised.

NUH's Ms Wong adds that while large doses of caffeine result in a quicker buzz, these effects will wear off just as quickly. Such a habit can also lead to increased tolerance, resulting in withdrawal symptoms when caffeine intake is reduced.

Undergraduate Claudia Koivuaho, 20, says that while one can easily see and measure sugar, caffeine is a more elusive concept. She adds that while sugar is known to significantly increase the risk of pre-diabetes, the long-term effects of caffeine are less apparent.

"You might think caffeine won't affect you much until you actually experience the symptoms. You have to get to that point to realise its impact," she says. "Still, I don't foresee myself being able to complete my assignments without coffee, to be honest."

Wong suggests spreading caffeine consumption throughout the day for a steadier increase in energy levels and alertness. In the case of suspected caffeine overdose, she advises monitoring symptoms, drinking plenty of water and stopping all caffeine consumption. Medical help should be sought if severe symptoms occur.

Not just to stay awake

For some, caffeine consumption is not just about staying awake. It has become a social activity and a part of their lifestyle.

Account executive Larissa Nair was 10 when she started drinking tea.

"My mum would take me to cafes for high tea, and when Milo or hot chocolate was not available, I was introduced to chamomile, white or other floral tea that did not have too much caffeine," the 24-year-old says.

"I did not start drinking coffee until I was 20. My mum always advised me to avoid coffee in case I got addicted, but now I feel like I am addicted to tea. It is like flavoured water to me," adding that she likes her tea bitter.

Kaur started drinking coffee at 14 when her school canteen began selling bottled iced milk tea, which she disliked. "However, I wanted to feel included since everyone was drinking it," she says. "So, when bottled iced coffee became available, I jumped right in."

Her mother would make coffee for her to take to school in a tumbler. "I was only 15 or 16 then, and I was surprised at how quickly one could get addicted to a drink," Kaur says. "Because of that, I have always seen caffeine as something not entirely good and make sure I never overdo it."

Leong likes how people mingle while queueing for coffee, and sees it as a social event. "Unlike alcohol, coffee allows you to bond with others in a more formal and not crazy way," she says.

Koivuaho agrees, saying: "I went to School of the Arts with my younger sister, who dances. One of the things we always do, after her many hours of dance practice, is to drink bubble tea together.

"It became a ritual for us before heading home. Even now, after we have both graduated, I still see bubble tea as a very social activity. It is a wonderful way to spend time with each other."

Wong points out that caffeine content in coffee and tea can vary depending on how they are prepared. Bubble tea, which uses tea as its base, also contains caffeine but not as much as coffee. Nonetheless, the addition of ingredients such as pearls, syrup and sugar poses other health risks.

"These ingredients can contribute to weight gain as they typically contain significant amounts of sugar and calories. This can increase the risk of metabolic abnormalities." She advises young people not to rely too much on energy drinks and other caffeinated beverages.

"It is important to read nutritional labels when purchasing products, be aware of the negative effects of excessive caffeine consumption and limit caffeine intake to recommended amounts," she says.

There are other ways to stay alert, she adds. These include regular exercise to increase energy levels, staying hydrated to prevent fatigue and taking power naps if necessary. 

A Nutri-Grade for caffeine?

Habits can be hard to break. None of the Gen Zs interviewed say they would change the way they consume caffeine, even if a system similar to Nutri-Grade was imposed.

"I never considered quitting coffee. Because if not coffee, then what? Water? That sounds a bit boring to me," says Leong. "I like to think that coffee is healthier than bubble tea."

Although coffee makes her hands shake and affects her work as a stylist, Kaur has no intention of giving up the habit too. "I have attention-deficit hyperactivity disorder, and caffeine calms my brain down and makes it less chaotic," says the coffee enthusiast who makes her own brew.

"As a coffee lover, I am aware of what I am putting into my body. I know caffeine is a stimulant, like nicotine, just without the age limit."

On nights when he is not working but still craves the taste of coffee, Aidan opts for the decaffeinated alternative.

"What I realised is, the later I drink my coffee, the less tired I become, but it also makes it harder for me to sleep at night. So, there is a trade-off, and I am gambling my sleep away," he says.

He thinks that a Nutri-Grade system will not change the way he consumes caffeine; in fact, it might have the opposite effect.

"If I go to a cafe and I am told that my daily threshold is 400mg, and I have to choose between a cup of coffee with 300mg and one with 800mg, I will choose the latter to make it worth my money. This is how I see it because either way, I am paying for the caffeine, so why not get more?"

Leong agrees, adding that price is probably the only factor that affects her caffeine consumption. She admits she is not aware of the caffeine content in her drinks, but even if she knew, it would not change much for her.

"I will knowingly put myself at risk rather than doing it unknowingly," she says.

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This article was first published in The Straits Times. Permission required for reproduction.