Drinking tea is good for you. Regular consumption is linked to a lower risk of death from cardiovascular disease, stroke, and heart disease, and the combination of protective plant compounds, a moderate caffeine dose, and a unique amino acid makes tea one of the most well-studied beneficial beverages. That said, how much you drink, what type, and when you drink it all matter.
What Makes Tea Protective
Tea leaves are packed with polyphenols, a class of plant compounds that act as antioxidants in your body. They work by donating electrons to unstable molecules called free radicals, neutralizing them before they can damage your DNA, proteins, or cell membranes. This reduces the kind of low-grade cellular damage that, over years, contributes to chronic disease.
Green tea is especially rich in a potent antioxidant called EGCG, which does more than just mop up free radicals. It also ramps up your body’s own antioxidant defense systems and suppresses inflammatory signaling at the cellular level, reducing the production of proteins that drive inflammation. Black tea contains less EGCG but has its own set of antioxidants (theaflavins and thearubigins) formed during the oxidation process that turns green leaves dark.
Heart Health and Longevity
The strongest evidence for tea’s benefits centers on heart health. Data from the National Cancer Institute shows that higher tea consumption is associated with a lower risk of death from cardiovascular disease, ischemic heart disease, and stroke. A large study on beverage intake found that people who drank an optimal total of 7 to 8 cups per day of coffee, tea, and water combined had a 28% lower risk of death from all causes compared to those who drank fewer than four. The most protective combination was a balanced mix of coffee and tea in roughly a 2:3 ratio.
There’s a ceiling, though. When total intake of coffee and tea exceeded nine cups per day, especially if those drinks replaced plain water, there was a potential increase in cardiovascular mortality risk. More is not always better.
Focus Without the Jitters
Tea contains caffeine, but less than coffee. An 8-ounce cup of brewed black tea has about 48 mg of caffeine, while green tea has around 29 mg. For comparison, a standard cup of brewed coffee delivers roughly 95 mg. This moderate dose contributes to alertness without the sharp spike and crash many people experience with coffee.
What sets tea apart is an amino acid called L-theanine, which works alongside caffeine in a way no other common beverage replicates. In a controlled study of sleep-deprived young adults, a combination of L-theanine and caffeine (at doses comparable to a few cups of tea) significantly improved accuracy on attention tasks and sped up reaction times by about 38 milliseconds more than a placebo. Brain wave measurements confirmed that participants were processing information faster and filtering out distractions more effectively. Separate research has found that L-theanine boosts alpha brain wave activity in areas tied to visual processing, a pattern associated with calm, focused attention. Doses of L-theanine well above what you’d get from tea have been used in anxiety disorder trials with no significant adverse effects reported.
The Blood Sugar Question
You might see claims that tea improves blood sugar control, but the picture is more complicated. A study published in BMJ Open Diabetes Research & Care found that tea drinkers actually had slightly higher blood sugar levels after a glucose tolerance test, and tea consumption was associated with a 21% higher odds of glucose intolerance after adjusting for other factors. People who drank strong tea had even higher odds (76% greater risk), and those who had been drinking tea for more than 10 years showed increased risk as well. Insulin secretion markers were 7% to 13% lower in the tea-drinking group.
This doesn’t mean tea causes diabetes. The relationship is nuanced and may reflect habits that accompany heavy tea drinking, or the effects of specific compounds on insulin-producing cells. But it does mean you shouldn’t count on tea as a blood sugar management tool.
Iron Absorption and Timing
Tea’s tannins can interfere with your body’s ability to absorb plant-based (non-heme) iron, the type found in beans, spinach, and fortified grains. In one study, iron absorption dropped from about 50% when consumed with water to just 24% when consumed with tea. That’s roughly half the absorption lost.
If you’re at risk for iron deficiency, or if you follow a vegetarian or vegan diet, this matters. A practical fix is to drink your tea between meals rather than with them, giving your body time to absorb iron from food without interference. Pairing iron-rich meals with vitamin C (citrus, bell peppers) also helps counteract the effect.
Does Adding Milk Cancel the Benefits?
No. A study from Wageningen University gave 18 volunteers black tea, black tea with milk, green tea, or water and measured blood levels of key antioxidants afterward. Adding milk did not change the absorption of flavonols (quercetin and kaempferol) at all. A separate analysis confirmed that the absorption of catechins was also unaffected. So if you prefer milk in your tea, there’s no reason to stop.
Getting the Most From Your Cup
How you brew tea affects how many antioxidants end up in your cup. Research testing different steeping times found that longer brewing extracts more polyphenols. For green tea (both loose leaf and bags), black tea bags, white tea, and several herbal varieties, 15 minutes of steeping produced the highest antioxidant activity. That’s considerably longer than most people steep, so even pushing your brewing time from 3 minutes to 8 or 10 will increase the polyphenol content meaningfully.
Temperature matters too. Green tea performs best at around 75°C (167°F) for loose leaf, while black tea benefits from higher temperatures around 95°C (203°F). The simplest rule: for green tea, let boiling water cool for a few minutes before pouring. For black tea, use water just off the boil.
Which Type of Tea Is Best
All true teas (green, black, white, and oolong) come from the same plant and share a core set of beneficial compounds. The differences come down to processing. Green and white teas retain more catechins because they undergo minimal oxidation. Black and oolong teas develop different antioxidants during their more extensive processing. None is dramatically “better” than another for general health.
Herbal teas (chamomile, peppermint, rooibos) are a different category entirely. They don’t come from the tea plant and lack the specific compounds like EGCG and L-theanine discussed here. Some have their own benefits, but the cardiovascular and cognitive research applies to true tea.
For most people, 3 to 5 cups of tea per day is a reasonable range that aligns with the amounts studied in positive health outcomes, keeps caffeine intake moderate, and avoids the diminishing returns seen at very high intakes. If you’re sensitive to caffeine, green tea’s lower dose (29 mg per cup versus 48 mg for black) makes it easier to drink throughout the day without disrupting sleep.