Written by Robert Verkerk
So, is tea drinking good for you? As is so often the case when it comes interpreting the health sciences and the benefits, or risks, of natural products, consensus isn’t easy to come by.
Have you had your cup of matcha or green tea this morning? Or perhaps you’re on your sixth for the day — delighting in the benefits of washing all those catechins, flavonoids and other polyphenols through your body at regular intervals? Or you’ve gone down the black tea or ‘builder’s’ brew route…..contributing to the 165 million cups of tea consumed daily in Britain alone?
Is tea drinking good for you?
So, is tea drinking good for you? As is so often the case when it comes interpreting the health sciences and the benefits, or risks, of natural products, consensus isn’t easy to come by. Tea drinking is no exception. There are a multitude of reasons for the discrepancies in view, among them: the results from different studies are often inconsistent and don’t always show benefits; the natural products under investigation are often not sufficiently well characterised to allow meaningful comparisons to be made; different population groups experience different benefits and risks; there are discrepancies between the findings from lab studies versus those on human populations, and, last but not least; there are simply not enough high quality human studies covering the gamut of effects that different teas can have on the body.
Despite this seeming quagmire of evidence, conflicting results and divided opinion on tea drinking, there is some key information that can be teased out. This article serves to address some of the key questions relevant to tea drinkers, including: how and why tea drinking can help to keep you healthy, which teas might be better for you than others, and when and how much tea you should consider drinking daily?
To avoid any confusion, all references to tea in this article refer to use of the leaves of the tea plant, Camellia sinensis. Both green tea and black tea come from leaves of the same plant, although different parts of the leaves are used for different teas, and post-harvest treatment can vary hugely. Green tea is not fermented; the leaves are simply withered and steamed before being dried. Black and oolong teas are both crushed and fermented in various ways. Matcha is simply a powdered green tea, so instead of only benefiting from the compounds that are infused into water during the brewing process, the powdered tea is consumed in its entirety, so increasing the amount of beneficial phytochemicals, vitamins, minerals and amino acids consumed in a given volume of tea.
Tea as an antioxidant source
Oxidation happens when oxygen atoms (radicals) bind to elements or compounds, be they complex organic molecules or simple elements. Rust is an oxidation product that develops on the surface of iron or steel when exposed to oxygen. Our bodies are also susceptible to oxidation, and the result is the production of radical oxygen species (ROS), sometimes also referred to as ‘free radicals’, that if not scavenged by antioxidants produced naturally within our bodies or consumed in our diets, can lead to excessive oxidative stress. Many metabolic processes rely on a degree of oxidation to trigger a particular beneficial response, such as an immune response or wound healing. But oxidation is generally short-lived and counteracted by antioxidants which scavenge or quench the ROS. Uncontrolled oxidative stress, which can be thought of as ‘rusting from the inside out’, has been shown to increase our risk [http://www.ncbi.nlm.nih.gov/pubmed/24969860] of many chronic diseases, including heart disease and cancer, as well as contributing to premature ageing.
Making sure there is an adequate supply of antioxidants in the body is one of the best ways of guarding against oxidative stress, as well as managing related processes like a healthy inflammatory response and a resilient immune system.
In essence, we have two main antioxidant systems, an endogenous one in which we produce our own antioxidants internally, and en exogenous one, which relies on us consuming antioxidants in our diets and through drinks and beverages.
Appraising the science of antioxidants in tea
While tea supplies some essential nutrients, such as certain vitamins and minerals, and amino acids, the most important group of compounds in teas found to deliver beneficial effects are the flavonoids and other polyphenols that can act as antioxidants in the body. Different studies quote differing ‘horse power’ ratings for the antioxidant capacity of teas. Many of these are the result of laboratory or ‘test tube’ studies in which the antioxidant capacity of a given tea, or tea extract, has been measured according to its ability to ‘quench’ particular ROS (notably peroxyl, hydroxyl, peroxynitrite, superoxide anion, singlet oxygen or hypochlorite radicals). The most common kind of test is one called an ‘ORAC’ assay which stands for ‘oxygen radical absorbance capacity’. The assay was developed by one of the leading antioxidant testing facilities in the world, Brunswick Laboratories in Southborough, MA, USA.
The ORAC assay evaluates the antioxidant capacity of a test material under laboratory (in vitro) conditions notably against peroxyl radicals. It measures the value as Trolox equivalents (TE), usually expressed by weight of a given food or ingredient or per serving, and includes both inhibition time and the extent of inhibition of oxidation. There are various different types of ORAC assay, including hydrophilic (H-ORAC) and lipophilic ORAC (L-ORAC) assessments for water soluble and fat soluble antioxidant compounds respectively. Total-ORAC (Table 1) takes into account the ROS scavenging capacity of both the hydrophilic and lipophilic components.Most recently, Brunswick has developed a Cellular Antioxidant Assay (CAA) which measures antioxidant capacity of a test material within a human cell culture. While this test still doesn’t equate to a human clinical study, it is an important step closer to deriving a more realistic perspective of how a natural product might act as an antioxidant within the human body.
Despite its shortcomings, the ORAC test has long been regarded as a laboratory standard for determining the relative antioxidant capacity of natural products, although it has also been misused or misinterpreted by some given that ORAC values cannot be regarded as having a direct bearing on human health because antioxidant compounds are absorbed to differing extent (i.e. have different bioavailability), others are subject to chemical transformation in the body, there are genetic differences between individuals (so affecting both benefits and risks) and there may be a host of other interactions with other compounds present or consumed concomitantly. Some so-called antioxidants, when consumed at very high doses, may I some circumstances act as pro-oxidants, having the exact opposite effect to that which is expected. This has been shown for sustained very high doses of vitamin C. All these issues are very relevant when it comes to tea and its benefits.
In short, an ORAC lab test provides information about the theoretical antioxidant potential of a substance outside the body. This can be very useful for phytochemical profiling or quality control. The ORAC value does not, however, tell you anything about how the antioxidant substances are absorbed through the digestive tract or how they may subsequently interact in the bloodstream, in different tissues or in particular organs.
A number of other antioxidant assays are also quite often used to test antioxidants, including ferric reducing antioxidant power (FRAP) assay and the Trolox equivalence antioxidant capacity (TEAC) assay. These assays generate very specific data linked to specific antioxidant properties and so cannot be compared with each other or with ORAC values.
Table 1, based on analyses reported by the US Department of Agriculture (USDA), shows that brewed green and black teas have modest antioxidant capacities when measured in a laboratory. For a given volume, they are greater than beverages like apple juice, on par with unsweetened (but not blended, sweetened) cranberry juice, but somewhat less than well-known antioxidant ‘superfoods’ such as pomegranate, goji berries and even red wine. Additionally, ready-made teas were found to have substantially lower antioxidant capacities compared with brewed teas.
|Black tea, black, ready-to-drink (plain & flavoured)||313||170||590||9||Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422.|
|Black tea, brewed, prepared with tap water||1128||–||–||1||Welch Foods, Inc. 2006. Unpublished Data.|
|Green tea, brewed||1253||–||–||1||Welch Foods, Inc. 2006. Unpublished Data.|
|Green tea, ready-to-drink||520||320||610||11||Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422.|
|Black tea, with milk powder, ready-to-drink||264||100||480||7||Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422.|
|Apple juice, unsweetened, without added vitamin C||414||239||592||75|
Prior et al. J. Agric. Food Chem., 2003, 51:3273-3279; Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422; Welch Foods, Inc. 2006. Unpublished Data.
|Blueberries raw||4669||2746||9245||47||Cho et al.|
J. Sci. Food Agric., 2005, 85:2149-2158; Wang et al.
J. Agric. Food Chem., 2008, 56:5788-5794; Wolf et al. J. Agric. Food Chem., 2008, 56:8418-8426; Wu et al. J. Agric. Food Chem., 2004, 52:7846-7856.
|Cranberry juice, unsweetened||1452||852||2014||9||Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422.|
|Goji berry, raw||3290||–||–||1||Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422.|
|Black cherry juice||2370||2070||2970||9||Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422.|
|100% cranberry juice blend||865||865||865||5||Welch Foods, Inc. 2006. Unpublished Data.|
|Raw pomegranate juice, bottled||2681||2341||4444||13|
Prior et al. 2006. Unpublished data on pomegranate juice; Seeram et al., J. Agric. Food Chem., 2008, 56: 1415-1422;
Welch Foods, Inc. 2006. Unpublished Data.
|Pomegranate, raw||4479||–||–||3||Wolf et al.|
J. Agric. Food Chem., 2008, 56:8418-8426.
|Cocoa-mix, powder||485||–||–||2||Welch Foods, Inc. 2006. Unpublished Data.|
|Red wine, Merlot||2670||2670||2670||3||Seeram et al. J. Agric. Food Chem., 2008, 56:1415-1422.|
|Red table wine, Zinfandel||2400||2400||2400||3||Seeram et al. J. Agric. Food Chem., 2008, 56:1415-1422.|
|White table wine||392||318||484||12||Dávalos et al.|
J. Agric. Food Chem., 2004, 52: 48-54; Welch Foods, Inc. 2006. Unpublished Data.
Which teas have more antioxidants?
Tea contains a variety of constituents including the alkaloids caffeine, theobromine, and theophylline, polyphenols, tannins, trace elements and vitamins. Tea polyphenols, are the key antioxidant components, while the alkaloids, including caffeine, are nervous system stimulants.
The chemical composition of green or black teas vary according to the leaf size, the nature of processing, fermentation and drying, the infusion time. Even a particular type of tea can vary considerably, depending on factors like the prevailing climate during the growing season, the time or conditions during plucking, horticultural practices and the age and position of the leaf on the harvest shoot. The major polyphenols include catechins, epicatechin, epicatechin gallate, epigallocatechin-3-gallate (EGCG) and proanthocyanidins.
There is accumulating evidence for the role of tea as means of reducing the risk of serious chronic diseases such as heart and neurodegenerative diseases, cancer, metabolic syndrome and type 2 diabetes. Most of these beneficial effects appear to be related to the potent antioxidant and anti-inflammatory activities of EGCG, which typically comprises around 50% of the polyphenols present. Recent studies suggest EGCG may act by modulating the effects of the energy-producing organelles in cells, the mitochondria, as well as altering the cell cycle and mitochondria-related cell death (apoptosis).
Data from the Zutphen Elderly Study in the Netherlands revealed that tea drinking reduced the heart attack, but not stroke, risk among the elderly, the authors relating this to the high EGCG content especially in green teas (30% of the dry weight, as against just 9% of the dry weight of black tea). Both EGCG and other catechins have been implicated as the most significant antioxidants in tea. The bud leaf and the first leaves, as found in teas such as orange pekoe, tend to be richest in EGCG.
High-grade matcha green tea — as used in traditional Japanese tea ceremony — has the highest levels of L-theanine, thought to promote a state of alert relaxation.
Do we readily absorb the antioxidants in tea?
There has been considerable scientific debate about how easily catechins in tea are absorbed by the body. Most studies suggest bioavailability is far from complete, one study estimating key flavonol absorption being around 40% of those ingested. Bioavailability also appears to be reduced (up to 3.5 times) when tea is consumed along with food compared with when it is consumed on an empty stomach.
While we so often find ourselves asking for more, believing that ‘more is better’, in the case of antioxidants, this isn’t necessarily the case. There are two important aspects to consider. First, how long does the antioxidant effect last after consuming a single cup of green or black tea, and second, what is the extent and nature of the effect. On both counts, the results are impressive and remind us just how valuable tea drinking can be to our health.
While the caffeine levels typically peak within an hour of tea consumption, the catechin levels for someone having 4 cups of tea over a 6 hour period will typically peak in the bloodstream at 5 hours, with the super-catechin, EGCG, peaking after 24 hours. This means that regular tea drinking contributes to sustained levels of antioxidants in the bloodstream — a great way to reduce your long-term chronic disease risk and maintain neurological health.
For the over 90% of people who consume tea with milk, the good news is that the addition of milk to tea doesn’t compromise the bioavailability of catechins.
On that note, given you’ve got to the end of this article, perhaps you might consider making yourself a cup of matcha, green or even black tea before you resume your next task?