Tea is one of the most widely consumed beverages in the world, and for most people it’s perfectly safe. But it does come with a handful of genuine downsides worth knowing about, especially if you drink several cups a day or have certain health conditions. The main concerns involve caffeine, reduced iron absorption, stomach acid stimulation, and a few less common risks tied to fluoride, oxalates, and drinking temperature.
Tea Can Block Iron Absorption
This is one of the most well-documented downsides of regular tea drinking. Compounds in tea called tannins bind to non-heme iron (the type found in plant foods, eggs, and fortified grains) and make it harder for your body to absorb. The effect is significant: iron absorption can drop anywhere from 3% to 27% depending on whether you’re drinking tea with food or on its own. In one study of Indian women, drinking 200 mL of black tea with a meal cut iron absorption by 21%.
For most healthy people eating a varied diet, this isn’t a problem. But if you’re already low in iron, pregnant, or eating a mostly plant-based diet where non-heme iron is your primary source, drinking tea with meals could meaningfully reduce how much iron you’re actually getting. A simple fix: drink your tea between meals rather than with them, and adding milk appears to blunt some of the inhibitory effect.
Caffeine Adds Up Faster Than You Think
An 8-ounce cup of brewed black tea contains about 48 mg of caffeine. Green tea has roughly 29 mg per cup. Those numbers are modest compared to coffee (which runs 80 to 100 mg per cup), but if you’re someone who drinks four or five cups of black tea throughout the day, you’re approaching 200 to 250 mg of caffeine, enough to cause insomnia, anxiety, a racing heart, or digestive discomfort in sensitive individuals.
During pregnancy, this matters more. The American College of Obstetricians and Gynecologists recommends staying under 200 mg of caffeine per day, and the March of Dimes echoes that limit. Four cups of black tea would put you right at that threshold. If you also consume chocolate, soda, or any coffee, you could easily exceed it without realizing.
It Stimulates Stomach Acid
Tea is a potent trigger for gastric acid production. In one study, black tea without milk or sugar produced an acid response nearly equal to what you’d see from a maximal dose of histamine, a compound used clinically to test how much acid the stomach can produce. The effect is driven by tea’s direct chemical action on the stomach lining, not by caffeine alone.
If you have acid reflux, gastritis, or a sensitive stomach, this matters. Drinking strong tea on an empty stomach is the most likely scenario to cause discomfort. Adding milk and sugar reduces the acid-stimulating effect, and weaker brews are gentler than concentrated ones. The study found that tea brewed at three times normal strength had the greatest impact, so a typical cup is less aggressive, but still notable for people prone to digestive issues.
Very Hot Tea Raises Esophageal Cancer Risk
The risk here isn’t about tea itself. It’s about temperature. Research highlighted by Memorial Sloan Kettering Cancer Center found that drinking tea at 60°C (140°F) or higher is associated with increased rates of esophageal cancer compared to drinking it at lower temperatures. The World Health Organization classifies very hot beverages (above 65°C) as “probably carcinogenic” for this reason. The repeated thermal injury to the lining of your esophagus is what drives the risk.
This is most relevant in cultures where tea is traditionally consumed immediately after boiling. If you let your tea cool for a few minutes before drinking, or if you add cold milk, you’re largely avoiding this concern.
Fluoride Builds Up With Heavy Consumption
Tea plants naturally absorb fluoride from soil, and it concentrates in the leaves. When brewed with tap water, tea infusions contain between 1.6 and 6.1 mg of fluoride per liter, with an average around 3.3 mg/L. The tolerable upper limit for adults is 7 mg per day. If you’re drinking a liter or more of tea daily (roughly four to five cups), especially in an area with fluoridated water, you could approach or exceed that threshold over time.
Excessive fluoride intake over years can lead to dental fluorosis (mottled teeth) and, in extreme cases, skeletal fluorosis, which causes joint pain and stiffness. This is rare in Western countries but has been documented in populations that consume large amounts of brick tea, a compressed form common in parts of China and Central Asia. For moderate tea drinkers, fluoride from tea is not a realistic concern.
Oxalates and Kidney Stone Risk
Black tea contains oxalates, compounds that can contribute to calcium oxalate kidney stones, the most common type. A cup of black tea brewed for five minutes contains about 4.4 mg of oxalate, rising to around 6.3 mg if you let it steep for an hour. People prone to kidney stones are typically advised to keep total daily oxalate intake under 50 to 60 mg and avoid individual foods with more than 10 mg per serving.
By those standards, a few cups of tea per day contribute only a fraction of the daily limit. Researchers have concluded that even four cups of diluted tea would have a marginal impact on oxalate intake. If you’ve had calcium oxalate stones before, it’s worth being mindful, but tea alone is unlikely to push you over the edge unless your overall diet is already high in oxalate-rich foods like spinach, rhubarb, and almonds.
Heavy Metals and Pesticides
Tea leaves can accumulate trace metals like aluminum, lead, and manganese from the soil. This sounds alarming, but the actual intake from drinking tea falls well below safety thresholds. One study calculated the hazard quotient for aluminum, lead, cadmium, manganese, and copper in tea and found all values significantly lower than the risk level, concluding that typical tea consumption does not result in excessive metal intake for the general population.
Pesticide residues tell a similar story. In a screening of 20 commercially available tea samples for 12 different pesticides, only one compound was detected (in 30% of samples), and its concentration was far below regulatory limits. The other 11 pesticides weren’t found at all. While organic tea eliminates this concern entirely, conventional tea appears to carry minimal pesticide risk based on current monitoring data.
Who Should Be Most Careful
Tea’s downsides are real but context-dependent. The people most likely to experience negative effects are those who drink large quantities daily (five or more cups), those with iron deficiency or anemia, people with acid reflux or a history of kidney stones, and pregnant women watching their caffeine intake. For everyone else, moderate tea consumption, two to three cups a day, is unlikely to cause problems and comes with well-established benefits from its antioxidant content.
The simplest adjustments make the biggest difference: drink tea between meals to protect iron absorption, let it cool before drinking, and if you’re sensitive to caffeine, switch to green tea or decaf (which contains just 2 mg of caffeine per cup).