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Consuming tea in close proximity to meals may substantially reduce the bioavailability of iron—particularly non-heme iron derived from plant-based sources—due to the presence of polyphenols, primarily tannins, and oxalic acid, which form insoluble complexes with iron and thereby impede its efficient absorption in the small intestine. This issue is of particular concern to individuals following plant-based diets (vegans, vegetarians), patients diagnosed with iron-deficiency anemia, and pregnant women, whose iron requirements are elevated. These groups are advised to consider adjusting their dietary habits, such as consuming tea at least 1–2 hours apart from main meals, to mitigate the adverse impact on iron absorption.

Tea serves as a source of caffeine—a central nervous system stimulant—that can adversely affect both sleep onset and overall sleep architecture. A single cup may contain anywhere from 14 to 65 milligrams of caffeine, with concentrations varying based on the type of tea and steeping duration. Evening consumption poses particular risks, as the body’s natural preparation for restorative sleep may be disrupted. Prolonged steeping of loose-leaf teas further amplifies caffeine extraction, potentially leading to difficulties in falling asleep as well as increased sleep fragmentation throughout the night. For individuals experiencing insomnia, complete avoidance of caffeinated beverages in the afternoon and evening is strongly advised. Alternative strategies include limiting steeping time to no more than three minutes or opting for low-caffeine varieties, such as instant tea blends. Research indicates that even moderate evening caffeine intake can delay the onset of deep sleep phases, thereby diminishing the restorative quality of sleep [1, 2].

Scientific evidence suggests that caffeine may provoke irritation of the gastrointestinal mucosa, particularly within the stomach, which is significant in the context of conditions such as gastroesophageal reflux disease (GERD) or ulcerative mucosal lesions. Its consumption is advised to be limited in these cases. Similar restrictions apply to strong black tea, which also contains substantial amounts of caffeine. While studies have not definitively established a strong link between tea consumption and an elevated risk of developing reflux disease [3], it is important to emphasize that factors such as regular alcohol intake, nicotine dependence, and frequent use of nonsteroidal anti-inflammatory drugs (NSAIDs) exert a far more pronounced detrimental effect on gastric health [4]. Furthermore, prolonged steeping of tea may exacerbate pre-existing dyspeptic symptoms. Individual sensitivity to caffeine varies—some individuals may experience discomfort even with minimal doses, though these reactions are not universal among all patients diagnosed with reflux.

Tea leaves contain polyphenolic compounds classified as tannins, which exhibit both antiseptic and astringent properties when interacting with mucosal membranes. These bioactive constituents are responsible for the beverage’s distinctive, slightly astringent flavor profile with bitter undertones. While tannins serve a protective function within the gastrointestinal system by counteracting toxic agents, they may concurrently act as irritants to the delicate gastric lining, potentially triggering dyspeptic symptoms such as nausea. Although this reaction poses no serious health risk, it can substantially diminish daily comfort levels. Individuals predisposed to gastric sensitivity are advised to refrain from consuming highly concentrated tea infusions on an empty stomach. Instead, opting for milder brews supplemented with soothing natural additives—such as liquid honey and freshly squeezed lemon juice—can effectively mitigate potential mucosal irritation.

Caffeine consumption affects the action of certain neurotransmitters in the nervous system. High doses of caffeine can cause anxiety and worsen anxiety. Most of these statements relate to coffee, but tea also contains caffeine.

The gestational period necessitates heightened vigilance regarding caffeine intake, as this stimulant is not confined solely to coffee but is also present in tea, cocoa-based beverages, and cola drinks, thereby facilitating inadvertent exceedance of recommended daily thresholds. Furthermore, compounds found in tea may impede the absorption of micronutrients critical for optimal fetal development—most notably iron and folic acid [5]—which can exacerbate anemic conditions, directly impacting both maternal and fetal well-being. Empirical research has established a correlation between excessive tea consumption and diminished folic acid levels in the body, although no definitive causal link has been identified between tea drinking during pregnancy and the incidence of congenital fetal anomalies. Nevertheless, due to the caffeine content in tea, its consumption must be restricted, as daily intakes exceeding 50 mg may contribute to premature labor onset. Additionally, caffeine adversely affects fetal cardiac rhythm [6]. According to guidelines issued by the British Food Standards Agency, the maximum safe caffeine allowance for pregnant and breastfeeding women is 200 mg per day, whereas alternative sources suggest a higher threshold of 300 mg.

Dizziness and severe headaches may arise as a physiological response to tea consumption, a phenomenon that in certain instances is accompanied by nausea—a reaction previously documented in relation to other caffeine-containing beverages. In specific cases, drinking tea may also trigger migraine episodes, characterized by recurrent, throbbing head pain supplemented by additional symptoms such as heightened sensitivity to light (photophobia), excessive lacrimation, and persistent nausea. Common migraine triggers include tyramine-rich foods (e.g., chocolate, aged cheeses with mold), alcoholic beverages like red wine, histamine-laden products (such as fish and shellfish), and stimulants, including caffeine. Consequently, regular tea consumption—regardless of the variety (black, green, white, or herbal)—may induce or exacerbate headache symptoms in susceptible individuals.

The active compounds found in tea—namely theine and caffeine—are classified by the World Health Organization as psychoactive substances capable of inducing dependence when consumed in excessive quantities. While ongoing scientific debates persist regarding whether caffeinism should be formally recognized as a distinct pathological condition requiring clinical intervention, empirical evidence confirms that a subset of the population experiences withdrawal symptoms upon abrupt cessation of caffeinated beverage consumption. Common manifestations include persistent headaches, heightened irritability, and generalized anxiety, all of which typically subside following caffeine reintroduction. Surprisingly, however, the overwhelming majority of research focuses predominantly on coffee, cola-based soft drinks, and energy drinks, largely overlooking tea—a beverage of comparable global prevalence and, in certain cultures, even greater consumption than coffee. Although regular tea consumption poses minimal health risks for most individuals, specific high-risk groups must exercise heightened caution. Patients with gastrointestinal disorders, particularly those affecting the stomach lining, as well as individuals diagnosed with anemia, should limit tea intake due to its potential to exacerbate irritation and inhibit iron absorption. Pregnant women are likewise advised to monitor caffeine consumption closely, as excessive levels have been linked to adverse fetal development outcomes. Unlike coffee or energy drinks, however, tea rarely faces scrutiny from nutritionists. The prevailing recommendation remains one of moderation, coupled with attentive observation of the body’s individual responses to different tea varieties.