Improved mood, reduced risk of heart disease and diabetes … tea is linked to multiple health benefits. Many of us drink tea for the good things it does for us, but are all teas created equal?

What is it, what’s in it?
First, some quick background. Black, green, white and oolong teas all come from the same plant, Camellia sinensis. The colour and flavour then changes during processing and harvesting. After harvesting, black tea is exposed to high levels of oxygen, causing oxidation, which darkens the leaves. Green tea stays green because it isn’t oxidised, whereas white tea is processed the same way as green, but harvested earlier. Oolong could be described as the middle ground between green and black.

All are a good source of bioactives, compounds that aren’t an essential part of our diets but may have health benefits. The bioactives found in tea are L-theanine, caffeine and antioxidants. L-theanine gives you that calm feeling, caffeine makes you alert and antioxidants help prevent the cell damage caused by free radicals. Slightly more antioxidants means green tea is typically considered the most healthy option.

Is loose tea better? What about milk?
Surprisingly, teabags might be healthier than loose leaf tea. The lower grade teas, which make their way into teabags, include stems that contain more bioactives than leaves. Teabag tea is also cut more finely, improving extraction – which is why powdered matcha is so potent. Regardless of the type, the longer you brew, the more bioactives you extract, so patience in the key.

The debate rages on about when to add milk, and even if you should add milk at all. The UK’s Royal Society of Chemistry has suggested that adding milk first prevents clumping of milk proteins, which might give milk a stale taste. Historically though, milk was probably added first simply to stop the hot water from damaging the china.

Some scientists have suggested milk alters the antioxidant activity and health benefits of tea, but others have shown the same level of antioxidants reach the blood whether you drink with or without milk. Interestingly, lemon might actually increase the bioactive extraction, by making the water slightly acidic.

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Of course, more is not always better. Too much tea can lead to overconsumption of caffeine. Some caffeine may provide health benefits, but too much can cause insomnia, irritability and stomach upsets. The definition of “too much” varies, but is about 600 milligrams per day, which you could get from five to six cups of tea. Tannins in tea can also bind some nutrients, such as iron and calcium, stopping them from being absorbed. In other words, if you are low in iron you may want to hold off on the cuppa you have with breakfast.

What’s in a name?
Be wary, simply being called “tea” does not guarantee a product contains healthy bioactives. Pre-packaged iced teas and some instant teas have low levels of bioactives and can be high in sugar. Herbal and fruit teas, despite the name, don’t contain any actual tea, and properties vary dramatically. The use of word “tea” is not regulated by Australian food standards, so check the ingredients to see what you’re getting.

Herbal teas are often marketed for “detox” or weight-loss. This is somewhat accurate, as drinking tea may help regulate weight due to the stimulating effect of caffeine, and if you’re drinking tea to replace more calorie-dense drinks in your diet. Many teas also include herbal laxatives, which will see you lose a little weight quickly just by emptying your bowels. That said, drinkers are unlikely to see significant weight loss without also modifying the rest of their diet. Concentrated green tea extracts are also marketed with the same claims, but use caution: they have been linked to liver damage and failure, a big risk when there is little evidence they even work.

It is always tempting to look for the silver bullets. Tea is tasty and contains healthy bioactives, but whether it’s in brewed or extract form, it can’t cancel out other bad habits in our diets.

Dr Emma Beckett is Broadsheet’s nutrition columnist. A molecular nutritionist with a PhD in Food Science, she is a post-doctoral fellow in the School of Medicine and Public Health and the University of Newcastle. In a world of mixed messages she can be found busting nutrition myths and empowering people to critically assess nutrition information. She tweets at @synapse101.