Is caffeine good or bad for you?

More than 70% of us Kiwis drink at least one coffee a day, and around 24% drink three or more. For most of us, caffeine is a daily ritual, the thing that kickstarts our morning and powers us through the afternoon slump.

But have you ever wondered what life would be like without it?

A lot of my clients ask me the same things. Is it actually healthy? Am I drinking too much? Is it making my anxiety worse? Is it wrecking my sleep?

Let’s talk about it.

What caffeine actually does in the body

Caffeine is a natural stimulant found in coffee, tea, cacao, and energy drinks. Personally, I don’t drink caffeinated coffee, even though I’m a fast caffeine metabolizer, I’ve never felt that great drinking it, but I do enjoy a matcha which contains smaller amounts of caffeine paired with L-theanine.

Caffeine works by blocking a molecule called adenosine, the one that builds up in your brain throughout the day and signals when it’s time to feel tired. Block adenosine, and you feel more alert, focused and energised.

Caffeine also nudges your brain to release more dopamine and adrenaline, which is why that first cup can feel so good.

But here’s the catch, caffeine doesn’t actually give you energy. It delays tiredness. And when the caffeine finally wears off, that’s when the crash hits.

Why caffeine affects everyone so differently

Your response to caffeine is largely genetic. A gene called CYP1A2 determines how quickly your liver breaks caffeine down.

• Fast metabolisers clear caffeine in around 4 hours
• Intermediate metabolisers take 4-6 hours
• Slow metabolisers can take 9+ hours (some studies show 8-12+)

Around 50% of the population carries a variant that makes them a slow or intermediate metaboliser, often without knowing it.

Here’s what that means in real life. If you’re a slow metaboliser and you have a coffee at 2pm, roughly half of that caffeine is still active in your system at bedtime, blocking the adenosine your brain needs to wind down for sleep.

If caffeine makes you feel jittery, anxious, or you struggle to sleep even after a morning cup, there’s a good chance you’re a slow metaboliser.

Other factors also affect how you respond to caffeine, including the state of your nervous system, adrenal health, age, medications and pregnancy, all of which can slow metabolism further and increase sensitivity.

The potential benefits

When it comes to coffee specifically (not caffeine on its own), research points to some genuine benefits from moderate consumption, largely because coffee also contains polyphenols and antioxidants alongside the caffeine.

Moderate coffee consumption has been linked to:

• Improved focus, alertness and cognitive performance
• Reduced risk of type 2 diabetes
• Lower risk of Parkinson’s disease
• Reduced risk of depression in moderate amounts
• Some protection against Alzheimer’s disease, particularly in women
• Enhanced exercise performance, especially for endurance activities (research suggests 3-6mg per kg body weight around an hour before exercise as the sweet spot)

Important caveat – these benefits are linked to coffee, not energy drinks or heavily sweetened caffeinated beverages.

The potential downsides

Depending on your sensitivity, caffeine can also cause:

• Jitteriness, anxiety, heart palpitations or irregular heartbeat
• Disrupted sleep, especially if you’re a slow metaboliser
• Digestive upset (caffeine has been associated with worsening IBS symptoms and acid relux)
• Short-term spikes in blood pressure
• Increased anxiety, and in high doses (around 5+ cups), it can trigger panic attacks in some people

Slow metabolisers who drink 2-3+ cups of coffee per day have shown a significantly higher risk of non-fatal heart attack and hypertension compared to fast metabolisers.

Extra considerations for some

If you’re pregnant or breastfeeding, keep caffeine under 200mg per day. Caffeine metabolism slows dramatically during pregnancy, by the third trimester, caffeine’s half-life can double or triple. High caffeine intake in pregnancy has been linked to lower birth weight. For breastfeeding mums, caffeine passes into breast milk, and newborns metabolise it very slowly.

If you have a mood or mental health condition, you may be more sensitive to caffeine. While moderate consumption has been linked to lower depression risk in some studies, others show it can increase anxiety.

If you’re on certain medications, including some antidepressants, beta blockers or muscle relaxants, talk to your doctor, as caffeine can interact with these.

How to tell if caffeine is working for or against you

Track your symptoms for a week – how much you’re having, when you’re having it, and how you feel. Pay attention to:

• Jitteriness or heart palpitations
• Anxious thoughts
• Afternoon energy crashes
• Difficulty falling or staying asleep
• Digestive upsets

These are subtle signs that caffeine might not be working in your favour.

If you’re sensitive, prone to sleep issues, or fall into any of the categories above, aim to keep caffeine under 200mg per day (roughly one standard coffee), after a meal, and stop by midday.

Try a reset

Sometimes the most powerful thing you can do is take a break. Cutting caffeine for 2-4 weeks lets your system recalibrate without artificial stimulation.

Some of my clients realise they’ve been leaning on caffeine for “energy” which actually for them has masked nutrient deficiencies, blood sugar imbalances, or burnout. Once those are addressed, their energy comes back naturally. Many report feeling more focused, less irritable and more relaxed once they’ve reset.

It’s important to know that caffeine withdrawals (headaches, fatigue, irritability) can hit for a few days. But by the end of week one, most people feel calmer, clearer and more balanced.

The bottom line

Caffeine isn’t inherently good or bad. It’s about how your body responds to it, how much you’re having, and when.

While your friend or partner might drink three + coffees a day with no issue, your body might respond very differently. Tune in to your own signs and adjust accordingly, that’s what real, sustainable health looks like.

References

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