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One of the features of cultures with longevity, such as in Greece or Japan, is drinking tea. Tea is the second most popular beverage next to water and is a convenient source of polyphenols for many individuals. Green, black, white, oolong, and pu-erh tea all come from the plant Camellia sinensis and are considered “true” types of tea. Though all five teas originate from the same plant, they differ in preparation method, which can include oxidation and fermentation. For example, black tea is fully oxidized, whereas green tea is not oxidized; pu-erh tea is fermented and therefore contains probiotics; and white tea undergoes the least processing.
Bioactive compounds, including phenolic acids, catechins, flavonoids, and tannins, are responsible for the health benefits of tea as they confer antioxidant, anti-inflammatory, and even anti-cancer properties. Among many other health benefits, tea can protect against atherosclerosis and liver disease, improve insulin resistance, regulate the gut microbiota, and induce cell apoptosis. In fact, a review states that as little as two cups of tea per day may decrease the risk of cardiovascular disease.
Tea can even improve brain function, as is seen with the amino acid L-theanine found in tea leaves. A study involving 52 Japanese men and women who received either a placebo or 100 mg of L-theanine for 12 weeks found that L-theanine may enhance working memory and executive function. There is a possible synergistic effect between L-theanine and caffeine in green tea, in which case L-theanine is considered a depressant, and caffeine is considered a stimulant.
For many people, tea is an affordable source of health-promoting phytochemicals. However, there are some factors to consider in order to maximize the health benefits of tea.
How to Choose Tea
Choose high quality teas that are not contaminated with heavy metals. In a study that analyzed 30 different teas, researchers found aluminum, lead, arsenic, and cadmium in all samples. When choosing tea, look for brands that use third party testing to identify possible contamination in their products. Examples of brands that use third party testing include Pukka, Organic India, and Buddha Teas.
Importantly, some tea bags are made of plastic, which can release micro- and nano-plastics during steeping. Micro- and nano-plastics have shown to accumulate in organs including the intestines, liver, and kidneys, and cause several health issues, including oxidative stress and neurotoxicity. Unbleached plant-based tea bags or loose-leaf teas are healthier choices than tea bags that use plastic. Ideally, if using tea bags, the bag will be sewn shut rather than stapled or heat-sealed. Tea bags that are heat-sealed often use plastic or a wheat-based product. Staples can be from a number of materials including iron, aluminum, and stainless steel and can be hazardous if accidentally ingested. Pukka teas use organic cotton to sew the bags closed and use organic strings for the tea bags.
Takeaway: Choose tea brands that test for contaminants. Loose leaf tea is best for avoiding plastics, staples, and gluten-containing adhesives. If using tea bags, choose brands that use plastic-free, unbleached tea bags and sew or tie bags closed rather than heat-sealing. Tea bags that are “pillow packs” or “pyramids” are often heat-sealed. Individuals with celiac disease should choose products that are certified gluten free.
How to Prepare Tea
Use filtered water to reduce exposure to toxicants, such as arsenic, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs), which may be present in tap water. In addition to reducing exposure via water source, be mindful of the materials used in tea kettles and mugs or teacups. Ideally, choose stainless steel, glass, and ceramic products for preparing and serving tea.
In the aforementioned study analyzing 30 different teas, all teas brewed for 3-15 minutes contained aluminum, and it appears that steeping tea for long periods of time may increase contaminant levels. When organic green tea and organic oolong tea were brewed for 15 minutes, aluminum levels rose above 10,000 μg/L, which is more than the upper acceptable daily limit of 7,000 μg/L.
Additionally, a study assessing the antioxidant capacity of 24 green teas found that re-steeping some teas up to six times can continue to yield high antioxidant capacity, whereas others do not appear to release significant active antioxidants after their first brew. Loose-leaf teas appear to have better antioxidant levels after six brews compared to bagged teas, and therefore have better reusability. Bagged teas may simply release more catechins, or antioxidants, during their first brew due to more finely ground leaf particles. However, there is no significant difference between the antioxidant capacities of loose-leaf vs. bagged teas. Loose-leaf tea that is re-steeped will have a lower caffeine content as most caffeine is extracted during the first brew.
According to the above study, optimal antioxidant extraction occurs when tea is brewed for 5-10 minutes at temperatures between 80-100 degrees Celsius compared to teas that are brewed for shorter periods of time at lower temperature. Another study found that brewing for 3 minutes at 85 degrees Celsius infused the maximum amount of catechins into green tea while low brewing temperatures (75 degrees Celsius) reduced polyphenol content. This study also found that at higher brewing temperatures (85 to 95 degrees Celsius), catechin concentrations did not increase with brewing time.
In general, caffeine content increases with steeping time. Caffeine content tends to be lowest in cold-brewed teas and highest in teas that are brewed in hot water and then iced (iced tea). Additionally, cold-brewed teas may have higher antioxidant activity compared to hot brewed teas.
Takeaway: Both loose-leaf and bagged teas are healthy choices, though loose-leaf tea has better reusability. Use filtered water and safe materials for preparing and serving tea and avoid steeping tea for longer than 10 minutes.
What to Add to Tea
Lemon. Lemon contains several flavonoids as well as vitamin C; according to research, adding lemon to green tea can increase the total polyphenol content of the beverage. Citrus peels, including lemon, orange, and grapefruit, can also be steeped in tea and have more antioxidant activity compared to other parts of the fruit. When using citrus peels, choose organic products and wash the fruit thoroughly first to reduce pesticide or pathogen exposure.
Milk. In a study investigating interactions among twenty commonly consumed foods, milk was shown to have synergy with black tea extract, which meant there was a significant overall effect on total antioxidant capacity when these foods were combined. However, milk and green tea extract had an antagonistic effect, resulting in a lower overall effect when combined. Therefore, milk may be best when served with black tea.
Honey. Honey is a natural sweetener with antibacterial, antidiabetic, and anti-inflammatory properties, and it is shown to modulate estrogen and protect against various types of cancer. It also contains phytonutrients, including kaempferol, quercetin, gallic acid, and ellagic acid. Honey may potentiate the antioxidants in tea by inhibiting lipid peroxidation and increasing the reducing power, or the ability to donate an electron.
Herbs & Spices. Similar to tea leaves, herbs and spices contain a variety of polyphenols and can be added to tea for a nutritious boost. For example, rosemary contains rosmarinic acid, which has anti-inflammatory properties and may enhance cognitive function. Rosmarinic acid is also present in a variety of other herbs including mint, lemon balm, and sage. Other tea additions may include cardamom pods and cinnamon sticks.
Takeaway: Flavor tea with nutritious additions including lemon, milk, honey, herbs, and spices.
How to Store Tea
A recent study investigated the effect of time on antioxidant activity of four common teas – black, green, white, and oolong. While the analysis showed variation in both the type of tea and the secondary plant compound (e.g. phenols vs. flavonoids), the initial antioxidant activity of the teas were nearly maintained after 90-120 days of storage. Beyond 330 days, only 60-75% of the initial antioxidant activity remained. Variations include findings that Oolong tea retains its phenol content for as long as 330 days, whereas its proanthocyanidin content declines sharply after 60 days.
Because polyphenols are sensitive to heat and light, it is best to store them in dark cabinets and away from heat sources, such as stoves.
Takeaway: Purchase tea in smaller quantities and use them as soon as possible to maximize antioxidant activity. Ideal tea storage is away from heat and light.
Does Tea Have Any Contraindications?
Caffeine is considered a stimulant and may be inappropriate for some individuals to use. Individuals with severe anxiety, cardiovascular disease or cardiac arrythmias, peptic ulcer disease, gastroesophageal reflux disease (GERD), liver and kidney issues, and seizures should use caution when consuming caffeine. Pregnant individuals should be mindful of caffeine consumption as only 200 mg daily is considered safe during pregnancy, though recent research suggests that lower amounts can impact child growth. Importantly, caffeine can come from a number of beverages and foods including, tea, coffee, soda, and chocolate.
Caffeine slows the metabolism of several drugs including antidepressants, antipsychotics, cardiovascular drugs and anticoagulants, some antibiotics, and NSAIDs, which can allow them to stay active in the body longer than intended. Caffeine in both tea and coffee can interfere with the absorption of the thyroid medication levothyroxine. Caffeine level varies by tea and is not easily categorized based on tea type; therefore, if caffeine content is an important factor, it is best to choose products that state the tea’s caffeine content and follow the brewing directions on the package.
Tea and coffee are decaffeinated through several methods including the use of solvents, water, and supercritical carbon dioxide. Though natural solvents used in decaffeination exist (e.g., ethyl acetate), a solvent known as methylene chloride may pose a risk to humans. Decaffeination using water may impact flavor. Supercritical carbon dioxide decaffeination is believed to be harmless and is advantageous over solvent use.
Additionally, tannins found in tea are believed to reduce the absorption of nonheme iron. However, it appears that long-term tannin consumption does not contribute to iron deficiency as much as tannins that are consumed alongside iron-rich meals. Therefore, for those who are at risk for iron deficiency, it may be a best practice to consume tea one hour apart from iron-rich meals to improve iron absorption.
Finally, store-bought “teas” often contain herbs instead of or in addition to tea leaves. Many herbs that are used in tea form, such as licorice, echinacea, and St. John’s Wort, have medicinal properties but are often contraindicated with certain medications or health conditions. Individuals with health conditions and those taking medications should pay close attention to ingredient labels and consult with their healthcare provider about how herbs can affect their health.
Takeaway: If you have any health conditions or take any medications, it’s best to consult with your healthcare provider about safe teas and pay close attention to ingredient labels.
If you have questions about which teas can best support your health, talk to your doctor, nutritionist, dietitian, or another member of your healthcare team for personal options based on your individual circumstances.
