Kiwis love a cuppa. As I write this, I'm enjoying one of several cups of green tea I'll have today. Tea is the world's most-drunk beverage, but New Zealanders have moved from being a nation of tea drinkers to lovers of coffee, which has overtaken tea as our favourite drink.

There's lots out there about the health pros and cons of tea and coffee. We probably know too much of either is going to give us more caffeine than we need; both tea and coffee contain caffeine, in varying amounts, and that includes my green tea.

Coffee generally has more caffeine than tea; the content depends on the variety and how it's roasted and brewed. Espresso has more caffeine than instant coffee, and cold-brew coffee can pack an even heftier punch. Large coffee drinks, of course, have more caffeine. Tea's caffeine content also varies, depending on strength.

There are no official guidelines on how much caffeine is okay; everyone processes it
differently, so it's a case of getting to know your own tolerance and practising moderation. If you're pregnant, you don't necessarily need to give up the coffees, but the general advice is to keep it to one or two a day.

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Caffeine has both positives and negative effects. It's know to support mental alertness – as anyone who's ever craved a morning coffee to get them going will know. Caffeine can help our concentration and working memory, and it's been shown to reduce sleepiness.

It can also potentially improve athletic performance and endurance. In a review published in 2015 researchers found that between 3mg and 7mg of caffeine per kilo of body weight increased endurance performance by around 24 per cent. It's thought that because caffeine stimulates and boosts alertness, it allows athletes to train harder, for longer. Regular exercisers may also experience a similar boost; have your caffeine an hour before a workout to get the best possible chance of a kick start.

Caffeine is often included in "fat burner" supplements. This is because of hype around its potential to help muscles burn more energy. But evidence for this is conflicting. Despite the mythology, living off coffee isn't a magical weight-loss solution.

The issue we're probably most familiar with with caffeine is its ability to affect our sleep.

Caffeine has a long "half life" – that means half of it is still going to be in our systems six hours or so after we've consumed it. An after-dinner coffee, then, could come back to bite you in the wee small hours. Everyone processes caffeine differently; some of us can cope with more with no apparent side effects. But when it comes to sleep, if we're waking feeling unrested even though we've slept all night, caffeine may be a reason. As with alcohol, it can interfere with the quality of our sleep, stopping us getting the really deep restorative sleep we need. This means, of course, we then reach for more coffee or tea, continuing the cycle.

Caffeine has both positives and negative effects. Photo / Getty Images
Caffeine has both positives and negative effects. Photo / Getty Images

On the plus side, coffee and tea both have other known positive effects. They're both associated with a reduced risk of cancer, thought to be from their antioxidant content. Both tea and coffee have also been linked with reduced risk for heart disease. It's probably fair to assume those benefits would be cancelled out if the coffee in question was a massive cream-topped, sugary coffee drink, or the tea an iced tea drink packed with sugar (these contain very little, if any, actual tea).

Green tea gets singled out, often, for its purported health benefits, and it's true there's been a lot of research in this area. But it's worth noting that black and oolong teas - being made from the same plant – also have similar benefits.

Even though green tea is good, more is not necessarily better. We're wise to steer clear of green tea extract (GTE), a concentrated form of green tea found in some supplements.

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Overdoses of this have been linked to liver damage and even death; a recent report from Australia told of a young man forced to undergo a liver transplant after taking protein shakes containing GTE. Stick to green tea in its leaf form to get the benefits without the risks.

Both tea and coffee – because of their antioxidant polyphenols and caffeine – can inhibit the absorption of iron from food. So if you're in the habit of having a cuppa with a meal, you may want to reconsider; have your drink half an hour after lunch (or before) to make sure you're getting the benefit of the iron in your meal.

Water, of course, is our best possible option for hydration, and we should make sure we drink water regularly through the day. But the bottom line on our daily cuppa is that regular teas or coffees - in the context of a plant-based, healthy diet - are all good.

• Niki Bezzant is editor-at-large for Healthy Food Guide. Follow her on Facebook or Instagram @nikibezzant