Lifestyle

Wired or tired: The truth about coffee and your health

Published on 21 October 2025

Should you sip that second cup of kopi or skip it? The way caffeine affects you depends less on willpower and more on your genes.

Two billion cups. That’s how much coffee the world drinks every day.

In Singapore, coffee is a daily ritual, from kopi at the hawker centre to lattes at the café. Energy drinks are catching on too, especially among younger people who often reach for them as a fast fix for long hours of work or study.

But here’s the catch. That same caffeine kick can send blood pressure climbing, spark palpitations or wreck your sleep. The twist? It is not just about how much you drink. It is about your genes.

“Caffeine’s impact varies greatly between individuals,” said Adj A/Prof Lim Toon Wei, Head of Community Cardiology, National University Heart Centre, Singapore (NUHCS). “There is no clear evidence of benefit or harm for heart health.”

He added, “Oftentimes, caffeine is wrongly blamed for causing a patient’s symptoms. The ultimate test is really whether it makes you feel better.”

For some, caffeine fuels focus. For others, it fuels anxiety. The difference lies in biology.

What caffeine does in the body

Caffeine is a stimulant. It boosts alertness and, in some people, disrupts sleep. Some studies suggest that moderate intake may benefit the liver and could reduce the risk of diabetes or Alzheimer’s disease.

It also increases urine production, which may cause dehydration. It can speed up bowel movements. On the cardiovascular system, it may raise your heart rate or trigger an irregular rhythm, felt as palpitations, and it can raise blood pressure.

Energy drinks deliver the same caffeine hit, but often in higher doses than coffee, sometimes packed into a single can. They also come with extra sugar and other stimulants, some less well studied, which can intensify side effects.

“While some patients may find that caffeine exacerbates their palpitations, this is not universally true, and studies of caffeine’s impact on heart rhythms have been inconclusive,” said A/Prof Lim.

When the buzz backfires: How to tell if caffeine is a problem

For patients with irregular heart rhythms, A/Prof Lim often suggests a short trial without caffeine to see if symptoms improve. “If it makes your symptoms better, then it would be a good idea to avoid caffeine,” he said, adding that many patients find that it makes no difference at all.

It is a similar story for those with high blood pressure, who are often already on the path to hypertension as they age. According to A/Prof Lim, many such patients need blood-pressure medication whether they cut out caffeine, because their readings remain difficult to control.

The warning signs can be sharper with energy drinks: racing heartbeats, jitters or poor sleep after just one can. For those already sensitive to caffeine, switching from coffee to energy drinks may make things worse, not better.

How much is too much?

As a general guide, up to 400mg of caffeine a day, or around four cups of coffee, is thought to be safe, said A/Prof Lim. Sensitivity varies. Some people feel unwell after one or two cups, or notice poor sleep if they drink caffeine after noon. If that sounds familiar, cutting back or setting an afternoon cut-off can help.

“My advice is to listen to your body,” he said. “If you feel worse after coffee, then quit it. But if you feel great, there is no reason to stop. You just have to pay attention to what it does to you to figure out what is safe for you.”

If you need a pick-me-up, a power nap of up to 15 minutes is often better than a caffeine boost. “More workplaces should be designed to allow this to happen,” A/Prof Lim added.

As an aside, A/Prof Lim is a coffee lover. His favourite brewing method is pour-over, which maximises the nuance of different beans and increases caffeine content. He believes his coffee habit has no impact on his own heart health.

“Being a coffee enthusiast makes me understand better the struggle that some patients have with giving up coffee,” he said. “It is a tough choice. At the same time, I am also more objective about it.”

The same advice applies to energy drinks. They count towards your 400mg total. A single can may equal one or two cups of coffee, so it is easy to tip over your daily limit without realising it.

The bottom line

Tailor your intake to how you feel and stay within daily limits. And remember, an energy drink is not a shortcut to alertness. The same rules apply: moderation, awareness and listening to your body.