tea and coffee

see also:

• caffeine
• diets and healthy foods

• drinking coffee and tea daily in moderation appear to have a variety of health benefits with significant reductions in all cause mortality
• regular caffeine intake results in tolerance (and also risk of withdrawal symptoms upon cessation):
  • in middle-aged adults who regularly drink coffee, there was little to no association between habitual caffeine intake, sleep quality, and daytime sleepiness¹⁾
  • lower regular intakes (< 750mg/day) result in incomplete tolerance
• an average shot of expresso coffee generally contains about 60mg caffeine, a cup of brewed coffee may have at least twice this much
• most adults can safely consume up to 400mg caffeine per day in tea or coffee and many may see beneficial effects at these levels²⁾

• coffee's bioactive compounds, particularly caffeine, polyphenols, and diterpenes, exert antioxidant, anti-inflammatory, antifibrotic, gut microbiome-modulating, and epigenetic-regulating effects, thereby slowing the progression of liver damage and reducing the risk of cirrhosis and liver cancer, but this beneficial effect apparently requires at least 3 cups per day ⁶⁾
• unfiltered coffee, including French press, Greek/Turkish, and Scandinavian boiled coffee, and to a lesser extent in espresso-based and Moka coffee contain cafestol which may raise serum cholesterol concentration - cafestol is not present in paper-filtered or instant coffee.
  • moka coffee shot typically contains about 1 to 2 mg of cafestol per cup (this could be largely eliminated by using a paper filter)
  • espresso shot usually contains about 1 mg of cafestol per cup/shot
  • French press coffee has 3.5 ± 1.2 mg of cafestol per cup
  • 5 cups per day of coffee types rich in cafestol have been reported to raise total cholesterol by roughly 0.2 to 0.3 mmol/L (ie. 0.13 mmol/L for each 10 mg cafestol consumed), increases LDL and lowers HDL
• the major polyphenolic and polyhydroxy compounds in brewed coffee also appear to inhibit the orphan nuclear receptor 4A1 (NR4A1) which may play an important role in the health-protective effects of coffee ⁷⁾
• adding milk can reduce the absorption of chlorogenic acids and other polyphenols by more than half - the antioxidant activity of coffee may decrease significantly with just a small amount of milk
  • a mainly milk coffee drink also adds to calorie intake
• 2 cups a day of black coffee (preferably early in the day to avoid caffeine's effects on sleep or GORD) appears to be beneficial, higher intake may have increasing adverse effects
  • although a stimulant, coffee does not appear to increase long term hypertension ⁸⁾
  • nevertheless, those with severe hypertension should probably limit coffee to 1 cup per day as a Japanese studied suggested higher cardiovascular mortality in this subgroup who drank 2 or more cups a day ⁹⁾
• coffee intake may reduce risk of uterine cancer
• coffee intake appears to improve the GIT microbiome¹⁰⁾
  • black filter coffee marginally reduces HbA1c levels by promoting Veillonella abundance in the gut microbiome whereas milk coffee or instant coffee doesn't¹¹⁾
• drinking 3-4 cups a day appears to slow cellular aging (slow the reduction in length of telomeres) in individuals with schizophrenia and affective disorders ¹²⁾
• the gut organism Lawsonibacter asaccharolyticus appears to be mainly found in coffee drinkers¹³⁾
• coffee (even decaffeinated) apparently via muscarinic effects also enhances the gastro-colic effect and the urge to defecate, hence a good reason to have it first thing in the morning
• a 2026 study of the UK Biobank suggests those who drink filtered coffee have a reduction in biologic aging markers but those who drink instant coffee do not have this benefit¹⁴⁾
• > 4 cups per day coffee intake in genetically slow metabolizers of caffeine were at ~84% higher risk of Parkinson's disease whereas fast metabolizers of caffeine who drank < 5 cups a day had 17% lower risk than heterozygous people who drank < 5 cups a day ¹⁵⁾
• moderate caffeine (1-3 cups coffee/day) consumption during midlife is associated with neuroprotective potential, particularly in reducing the risk of dementia with 65% lower risk of late-life dementia¹⁶⁾
• in a very large UK study over 11 years with avg age 56yrs published in 2021, 0.5-3 cups coffee per day was associated with a 12% reduction in all cause mortality, 17% reduction in mortality from cardiovasc disease, and 21% lower risk of stroke ¹⁷⁾

• drinking 2 cups a day of coffee appears to be beneficial for those with AF or in helping to prevent AF and cardiac failure
  • this study showed a 37% hazard reduction in AF recurrences ¹⁸⁾
  • appears to reduce risk of cardiac failure in patients with AF
  • appears to reduce risk of dementia in those with AF and in those without AF¹⁹⁾
• excessive caffeine intake however may cause rapid AF

• the Chinese have been drinking tea since about 2737BC
• in 1560, the Portuguese Jesuit missionary Father Jasper de Cruz was the 1st European to encounter tea and write about it
• tea was 1st sold as a health beverage in 1657 in London
• 1870, Twinings of England began to blend tea for uniformity
• 1908, the New York tea importer Thomas Sullivan inadvertently invented tea bags when he sent tea to clients in small silk bags and they mistakenly steeped the whole bags
• black tea is consumed principally in Europe, North America, and North Africa, whereas green tea is taken throughout Asia
• there are many constituents of tea ²⁰⁾
• the tea plant is a bioaccumulator of flouride and thus theoretically, excessive drinking may lead to possible fetal neurologic development effects from prenatal exposures especially in areas with already high flouride intakes due to flourinated water.²¹⁾

• generally contains about 40 to 70 mg of caffeine per cup
• 100% oxidized
• leaves are rolled, disrupting the cellular compartment and bringing phenolic compounds into contact with polyphenol oxidases, and the young C. Sinensis leaves undergo oxidation for 90–120 minutes before drying. During this process, which is referred to as “fermentation,” flavan-3-ols are converted to complex condensation products, such as theaflavins and thearubigins
• black teas have about half the amount of EGCG as does green teas as oxidation converts catechins to complex polyphenols such as theaflavins and thearubigins
• has been heavily linked to improved endothelial function and a reduction in LDL cholesterol and blood pressure
• those who drink three or more cups of black tea per day appear to have a significantly lower risk of stroke
• have much higher oxalate content (4-15mg, average 10mg per cup) than green teas and so have much higher risk of kidney stone formation
  • full oxidation breaks down cell walls and alters the chemical matrix, releasing more oxalates into the brew
• may contain high levels of aluminium

• contains about 30 to 55 mg of caffeine per cup
• partially oxidized (10-80%)
• manufactured mainly in Taiwan
• contains both the simple catechins found in green/white tea and the complex polyphenols found in black tea
• has theaflavins & thearubigins and moderate level of oxalates

• contains about 15 to 40 mg of caffeine per cup
• leaves are picked and harvested before they fully open
• leaves are steamed quickly after harvesting to prevent oxidation of polyphenols and then dried.
• minimally oxidized and thus retains the highest concentration of raw catechins with minimal complex polyphenols (similar to green tea)
• like green tea, it contains fewer complex tannins and low levels of oxalates

• may have benefits due to its caffeine, antioxidants and catechins like epigallocatechin gallate (EGCG) and L-theanine
• generally contains about 20 to 45 mg of caffeine per cup
• the leaves are steamed quickly after harvesting to prevent oxidation of polyphenols (the main flavan-3-ols are (–)-epicatechin (EC) and its gallate derivatives) and then dried
• green tea reduces systolic and diastolic blood pressure, especially in those with baseline systolic ≥130 mm Hg, and lowers total cholesterol and LDL
• 3-5 cups daily appears to lower stroke risk
• lowers risk of ureteric stone formation, particularly among men as long as no added sugars
  • significantly lower amount of soluble oxalates than black tea (1.36 mg per cup compared to nearly 10 mg in black tea)
  • EGCG protects renal tubular cells from oxidative stress and inflammation induced by calcium oxalate, which effectively prevents crystals from latching onto kidney tissues
  • catechins in green tea physically alter the shape of forming calcium crystals and by binding to the crystals, they make it much harder for the particles to clump together into larger stones
  • contributes to your total daily fluid intake increasing urine volume
• appears to improve HbA1c in type 2 diabetes with better glucose/insulin levels, and gut microbiome shifts aiding obesity prevention
• may reduce risk of a range of cancers, may inhibit a range of infections, reduce diarrhoea, reduce cognitive decline but also may reduce iron absorption, and as with black teas, may contain high levels of aluminium while high levels of EGCG may be hepatotoxic, cytotoxic to pancreas, and at extreme doses may induce goitres ²²⁾
• green tea concentrates or supplements may be seriously hepatotoxic

• it is likely that the milk and sugar used in chai tea may nullify its benefits - more studies are needed, especially in the south Asian population cohort²³⁾

• generally contains about 60 to 70 mg caffeine per serving because you ingest the whole leaf
• matcha has greater concentrations of caffeine and L-theanine (50-100% more per cup of brewed tea), more vitamin C, and matcha can contain up to 137 times more antioxidants than low-grade green teas and up to 3 times more antioxidants than high-quality green teas
• has a much higher concentration of oxalates than green tea so inceases risk of kidney stone formation
• matcha contains notably higher aluminium levels than green or black tea infusions due to consuming the whole leaf powder, which absorbs soil aluminium during shaded growth. Studies report matcha samples ranging 1,743–2,350 mg/kg, potentially exceeding EFSA's TWI (1 mg/kg body weight/week) with 2–3.6g daily intake (e.g., 1–2 portions), even as a sole source. Green and black teas, steeped as leaves, leach far less (<500 mg/kg or <13 µg/mL or < 3mg per 250mL cup in infusions), keeping exposure low²⁴⁾
• a 12-month RCT found 2g daily matcha improved social acuity (facial emotion perception) and trended toward better sleep quality in older adults with mild cognitive decline.²⁵⁾
• matcha appears to reduce the usual allergen-induced increased expression of c-Fos gene in the ventral spinal trigeminal nucleus caudali with resultant reduction in sneezing ²⁶⁾

• South American yerba mate
  • contains about 80 mg caffeine per cup
• guayusa

• herbal teas (other than the above caffeine teas)²⁷⁾
  • chamomile and lavender teas
    • may help relaxation and sleep
    • over 120 chemical constituents for chamomile have been identified, such as terpenoids, flavonoids, and essential oils
    • chamomile may lower associated risk of thyroid cancer and thyroid diseases
  • nettle and fenugreek teas
    • may enhance maternal milk production
    • stinging nettles contain phytosterols and are possibly beneficial in benign prostatic hyperplasia, and its biological activity involves sex hormone binding globulin (SHBG), a key regulatory molecule for testosterone and oestrogens
  • echinacea tea
    • may reduce URTI symptoms
  • spearmint tea
    • perceived to be effective as anti-androgen therapy for polycystic ovary syndrome (PCOS) / polyendocrine metabolic ovarian syndrome (PMOS) and appears to reduce blood levels of free testosterone in females and reduce PCOS-related hirsutism
  • hibiscus tea
    • may reduce BP
  • turmeric
    • often used as an anti-inflammatory to help in arthritis
    • high doses may be toxic
  • green lychee and rose
    • rose infusions contain high levels of gallic acid and total phenols, matching or exceeding the antioxidant capacity of green tea
    • rose extracts appear to help reduce inflammatory markers and that rose aromatherapy and tea improve emotional well-being and reduce stress
    • lychee components contain epicatechin and rutin, which may offer neuroprotective and anti-inflammatory properties
  • lemongrass and lime
    • high concentrations of total phenolics and vitamin C
    • citral in lemongrass
  • ginger
    • significant alpha-glucosidase inhibitory activity and β-Sesquiphellandrene which increases insulin sensitivity²⁸⁾
    • gingerol and shogaol compounds present in ginger root support gastric emptying and alleviate gastrointestinal distress and nausea
• rooibos²⁹⁾
  • obtained from the SouthAfrican plant Aspalathus linearis
  • three types of tea: green (unfermented), red (fermented), and black Rooibos teas.
    • unfermented green rooibos retains higher antioxidant levels than traditional fermented red rooibos
  • contains numerous minerals, especially flavonoids such as dihydrochalcones (aspalathin and nothofagin which make up 90% of the metabolites), phenylpropanoids, flavones, and flavonols (the 8-C and 6-C-β-D-glucopyranoside derivatives of luteolin and rutin are the major monomeric flavonoids found)
    • the only known natural source of aspalathin, a rare antioxidant
      • aspalathin targets several key enzymes involved in fatty acid synthesis and oxidation, leading to enhanced glucose and fat metabolism
    • the flavone analogues of nothofagin found in rooibos include vitexin and isovitexin, which are 8-C- and 6-C-β-D-glucopyranoside derivatives of apigenin, respectively
  • unlike black or green tea, rooibos is very low in tannins
  • has a much lower oxalate level than black tea (<2mg per cup vs 4-15mg per cup in black tea)
  • contains powerful antioxidants like quercetin and luteolin
  • according to some researchers, six cups of tea (1,200 ml) each day may have positive health benefits although studies to date are often conflicting and chronic high use may have adverse hepatic effects with elevated transaminases
  • can inhibit the angiotensin-converting enzyme (ACE), but does not seem to reduce BP over a 4 week period
  • can improve lipid profiles by lowering LDL-C, TG while increasing HDL
  • can increase melatonin levels
  • may stimulate osteoblasts while inhibiting the cells that break bone down although benefit in osteoporosis remains unproven
  • antispasmodic properties
  • naturally sweet and calorie-free
  • polyphenols in most teas including rooibos can affect the absorption of both heme and non-heme iron across cells
  • may result in iron deficiency if given to children in particular
  • may reduce urine volumes but does not seem to increase risk of kidney stone formation

• studies suggest that daily drinking coffee or tea reduces risk of osteoporosis by about 17-25% with tea seeming to have the greater benefit however excessive coffee at over 5 cups a day increased osteoporosis risk ³⁰⁾
• the effect may be due to catechins while caffeine theoretically can interfere with calcium absorption and bone metabolism although this effect appears to be minimal and further reduced by drinking it with milk

• those who drank two cups of coffee every day were at a 70% lower risk of developing polycystic ovary syndrome (PCOS) / polyendocrine metabolic ovarian syndrome (PMOS) symptoms than those who never drank coffee. Mechanistically, this protective role of coffee has been attributed to its effects on the metabolism of sex hormones like testosterone in the plasma. ³¹⁾
  • coffee contains high phenol levels that improve insulin sensitivity and alleviate hypersecretion. Reduced expression of the phosphatidylinositol 3-kinase (PI3K) pathway also decreases insulin sensitivity and improves β-cell function.