Aging is a continuous process associated with a higher likelihood of chronic disease and risk of increased morbidity and mortality [ 32 ]. The term successful aging incorporates many aspects of healthy living including quality of life, well-being, physical health, and the maintenance of cognitive function [ 33 ]. The role of dietary patterns on successful ageing is becoming better understood, with a current focus on the Mediterranean diet and its predominant constituents which include fruits and vegetables [ 34 ], and olive oil [ 35 ]. However, the potential health amplifying effects of tea consumption in the context of a Mediterranean style dietary pattern are unclear. Therefore, this study aimed to examine the association of tea consumption (green, black and no tea) on successful aging in people aged 50 years and over, living in Greece.

There is increasing evidence from epidemiological, clinical and experimental studies which suggest that the tea polyphenols (EGCG in particular) have various biological activities such as anti-fungal [ 19 ], anti-inflammatory [ 20 21 ] and antioxidative [ 22 ] properties. Habitual green tea consumption is associated with protection against several types of cancer [ 23 ] and lower all-cause mortality [ 24 ], while total consumption of tea has shown beneficial changes in psycho-cardiological outcomes, such as reduced risk of cardiovascular disease [ 25 ] and type 2 diabetes [ 26 ], lower blood pressure, reduced risk of developing hypertension in older adulthood [ 27 ], and decreased risk of cognitive impairment [ 28 ]. Black tea consumption is also associated with decreased risk of the development of cardiovascular disease in a ‘normal’ population [ 29 ]. Interestingly, two relatively recent meta-analyses of randomized controlled trials of black tea consumption on concentrations of serum cholesterols reported conflicting results with one showing no beneficial effects [ 30 ], and the other finding lower low density lipoprotein cholesterol (LDL-C) [ 31 ]. Nevertheless, higher tea consumption is considered part of a healthy lifestyle that may benefit health through various ways [ 25 29 ].

Green tea polyphenols are predominately comprised of four major catechins; in decreasing order of the amount present in tea, are: EGCG; (−)-epigallocatechin (EGC); (−)-epicatechin 3-gallate (ECG) and (−)-epicatechin (EC) [ 6 11 ]. The structure of these four catechins ( Figure 1 ) is characterized by multiple hydroxyl groups on two benzene rings. The gallocatechins (EGC and EGCG) have an extra hydroxyl group in the 5′ position of the B ring while the catechin gallates (ECG and EGCG) have an extra benzene ring with three hydroxyl groups [ 17 ].

Catechins are the most prominent and biologically active compounds in green tea, almost all of which are extracted during the tea brewing process. These compounds also provide a slightly astringent and bitter taste to green tea infusions with one cup (2.5 g/200 mL) containing approximately 150–200 mg of catechins in total [ 6 ]. The content of catechins in green tea can reach up to 30% of the tea leaves’ dry weight [ 13 ] with (−)-epigallocatechin 3-gallate (EGCG) being the most predominant, accounting for up to 60% of the total catechin content [ 14 ]. Nevertheless, the (−)-epigallocatechin (EGC) was also reported to be one of the major catechins found in several green tea samples [ 15 16 ], making EGCG and EGC, undoubtedly the major catechins present in green tea infusions. However, oolong, black and pu-erh teas are allowed to be fermented and oxidized, lowering their catechin content due to their conversion to theaflavins and thearubigins [ 3 ].

The manufacture of black tea involves the oxidative polymerization of the monomeric flavan-3-ols by the enzyme polyphenol oxidase, leading to the formation of bisflavanols, theaflavins, thearubigins and other oligomers. In contrast, during the production of green tea, freshly harvested leaves are quickly steamed or hot air-dried to inhibit the oxidizing enzyme, polyphenol oxidase, which prevents fermentation of the tea, yielding a dry and stable product. The blanching of leaves caused by this exposure of tea to hot steam or air is also responsible for the production of its pronounced green color [ 1 6 ]. The composition of green tea varies with the tea plant variety, harvest season, the position of the plucked leaves, horticultural practices, climate and geographical position [ 11 ]. However, all green teas are rich in polyphenols, including flavadiols, flavonoids and phenolic acids. The beneficial health effects of green tea are primarily ascribed to the biologically active polyphenolic components, especially the monomeric flavan-3-ols and the catechins [ 3 12 ].

Tea is one of the most widely consumed beverages worldwide, and global consumption ranks second only to water, well ahead of coffee, beer, wine and carbonated soft drinks [ 1 2 ]. Traditionally, the Chinese and Japanese people have believed that drinking tea promotes optimal health and longevity [ 3 4 ]. Therefore, it is not surprising that the health-promoting effects of tea have been intensively investigated over recent decades [ 3 6 ]. Prior to consumption, tea is generally processed and relatively recent research has classified tea originating from the plantinto seven types based on the type of processing as; ‘green’ (unfermented), ‘yellow’, ‘white’, ‘oolong’ (partially fermented), ‘black’ (completely fermented), ‘aged pu-erh’ (drastically fermented and aged) and ‘ripened pu-erh’ tea [ 7 8 ]. The global consumption of tea type varies, with black tea the most popular and favored in Western countries [ 9 ], green tea favored in Oriental countries, and oolong and pu-erh tea predominately consumed in China [ 3 11 ].

In Table 3 results are presented from logistic regression models that evaluated the association between the type of tea and the SAI level. Regarding the overall sample, those drinking green tea had 1.77 times higher odds (95%CI, 1.38–2.28) for having SAI over 3.58 compared to those drinking black tea, while those drinking green tea had 1.41 times higher odds (95% CI, 1.15–1.73) for having SAI over the median compared to those drinking black tea or the control group. Moreover, regarding those drinking black tea, the odds of having high SAI levels were 38% less than those drinking green or the control group. Similar logistic regression models based on gender showed that females and males drinking green tea had 1.75 and 1.79 times, respectively, higher odds (95%CI, 1.22–2.52 and 1.26–2.53 respectively) for having SAI over 3.58 compared to those females and males drinking black tea. Accordingly, those females and males drinking green tea had 1.36 and 1.50 times, respectively, higher odds (95% CI, 1.01–1.84 and 1.12–2.01 respectively) for having SAI over the median compared to those females and males drinking black tea or the control group. Finally, regarding those females and males drinking black tea, the odds of having high SAI levels were 38% and 33% less than those females and males drinking green or the control group, respectively.

A significant correlation was observed between the type of tea consumed and SAI score (Spearman rho = −0.232,< 0.001); thus, to further test the research hypothesis, multiple linear regression analysis was then applied ( Table 2 ). After adjustments ( Table 2 ) for age, sex, smoking habits and coffee intake, drinking, only black tea was negatively associated with SAI levels (b ± SE: −0.727 ± 0.055,< 0.001), whereas drinking green tea vs black tea was positively associated with SAI levels (b ± SE: 0.503 ± 0.078,0.001). Additionally, drinking exclusively green tea was positively associated with SAI levels (b ± SE: 0.225 ± 0.055,< 0.001) compared to not drinking at all tea (control group), whereas drinking black tea vs no drinking at all tea was inversely associated with SAI levels (< 0.001). Moreover, drinking green tea but no black or not drinking at all tea was not significantly associated with SAI levels (0.722). Black tea consumption compared with no tea at all was negatively associated with SAI levels (b ± SE: −0.807 ± 0.054,< 0.001). Therefore, it is concluded that the consumption of green tea among individuals aged > 50 years is associated with more favorable SAI levels ( Table 2 ).

In Table 1 some of the socio-demographic data, lifestyle and clinical characteristics of the ATTICA and MEDIS participants, categorized by type of tea consumption, are presented and used for the analyses. From the total of 1195 participants consuming tea, participants with green tea consumption were more frequently male (= 0.026) and physically active (< 0.001), while they were less likely to have hypertension (= 0.006) and more likely to have a higher level of the successful aging index (SAI) (< 0.001), as compared to those consuming black tea. No statistically significant differences were observed as regards cardiometabolic risk factors, adherence to the Mediterranean diet and smoking habits (all’s > 0.05).

3. Discussion

The present pooled analysis of two large-scale population-based studies conducted in Greece assessed the association between green and black tea consumption on successful aging in older people. The main findings demonstrated that the consumption of green tea was linked to a higher likelihood of successful aging based on the SAI compared with consumption of black tea following adjustment for potential confounding factors including age, sex, smoking, and coffee consumption. Interestingly, black tea consumption was negatively associated with successful aging compared with both green tea consumption and no tea consumption. Therefore, green tea, but not black tea, may be associated with enhanced healthy aging in older people in this population living in the Mediterranean region.

While both green tea and black tea are widely considered as healthy beverages, only green tea was associated with a higher SAI while in contrast, black tea was associated with a lower SAI. No differences in average daily consumption of the number of participants consuming green and black tea were observed. Although both green and black tea are high in antioxidants such as polyphenols and flavonoids, green tea possesses high amounts of catechins such as EGCG. In human trials, EGCG has been shown to promote fat oxidation and increase postprandial thermogenesis [ 36 ], while green tea consumption promotes lower total and LDL-cholesterol [ 37 ], and possesses anti-inflammatory properties [ 38 ]. When considering all these potential mechanisms of action and beneficial health effects of green tea consumption, it is intriguing that consumption of green tea is associated with the higher SAI. A relatively recent systematic review of the effects of green tea catechins on cardiovascular disease risk factors in human clinical trials suggests that BMI, hypertension, and plasma lipids may be improved, but several methodological issues limit the generalizability of the current evidence [ 6 ].

l -theanine ( l -THE) [2, l -THE is non-proteinous, and the most predominant amino acid found in green tea, accounting for over 50% of the total amino acid content. Concurrent with increasing commercial availability of the relatively pure l -THE [ l -THE in the prevention of caffeine-related side effects. Green tea also contains gamma-aminobutyric acid (GABA) which in animal models has been shown to decrease blood pressure [ l -THE and GABA, as well as many other unidentified potentially biologically active compounds present in tea [ in vitro through blocking of NFκB activation [ Although observed results relating to the differences between black and green tea are inconsistent, these observational associations could be potentially supported by substantial evidence from experimental studies investigating the antioxidant and vasodilation effects of the various tea compounds such as the-theanine (-THE) [ 1 39 ]. The-THE is non-proteinous, and the most predominant amino acid found in green tea, accounting for over 50% of the total amino acid content. Concurrent with increasing commercial availability of the relatively pure-THE [ 39 ], dose-dependent clinical trials have identified its hypotensive properties and negation of caffeine-induced effects related to increases in blood pressure [ 2 ]. Tea processing such as withering and fermentation are commonly applied to different tea varieties and only marginally influences the caffeine content [ 40 ], suggesting the importance of-THE in the prevention of caffeine-related side effects. Green tea also contains gamma-aminobutyric acid (GABA) which in animal models has been shown to decrease blood pressure [ 41 ] and improve antioxidative defenses and mood status [ 42 ] through the modulations of neurotransmitters responsible for antidepressant-like effects [ 43 ]. Besides the content of-THE and GABA, as well as many other unidentified potentially biologically active compounds present in tea [ 44 ], there are several other proposed mechanisms of action related to green tea consumption such as the suppression of the NADPH oxidase activity and reduction of reactive oxygen species in the vascular system [ 45 ]. Green tea polyphenols also possess anti-inflammatory propertiesthrough blocking of NFκB activation [ 46 ], and in animal models has been shown to decrease production of IL-6, TNFα, serum amyloid A [ 47 ] and S100β [ 48 ].

The positive results associated with green tea are potentially explained by the differences in the compositions of the two different tea varieties. It is well established that green tea contains higher levels of catechins in comparison to black tea, primarily due to the processing of tea leaves post-harvest [ 11 17 ]. Therefore, these higher levels of green tea catechins could be the driving factor for the lower levels of hypertension in this population sample, and similar findings have been reported in different population settings. For example, in Taiwanese men and women [ 49 ], habitual intake of green or oolong tea over 120 mL/day was associated with a reduced risk of developing hypertension. A recent systematic literature review with meta-analysis analyzed studies where green tea extracts high in catechins reduce systolic blood pressure, and total and LDL cholesterol levels [ 45 ]. Consumption of both tea varieties (black and green) can be beneficial in lowering blood pressure in individuals with prehypertensive and hypertensive ranges [ 50 51 ]. On the other hand, acute consumption of caffeine found in green and black tea may increase blood pressure, in participants who avoided caffeine for at least 12 h [ 52 53 ]. However, the relevance of these acute trials to regular tea consumption over the long term are still uncertain. Interestingly, short-term controlled clinical trials of regular tea consumption up to 8 weeks in normotensive individuals have shown that regular tea consumption does not have an overall effect on systolic or diastolic blood pressures [ 54 55 ]. Nevertheless, it is plausible that longer-term habitual consumption of tea can positively affect vasodilatory function and consequently results in altered vascular tone and blood pressure [ 56 ].

The population sample in the present study that consumed higher levels of green tea presented with fewer cases of hypertension but were also more physically active and also more likely to be male. Taking into consideration that SAI is constructed using ten attributes including the physical activity, BMI, depression, cardiovascular disease risk factors, as well as adherence to Mediterranean diet [ 57 ], it is intriguing that green tea consumption has shown higher odds for having SAI if compared to those of drinking black tea. Both groups consuming black and green tea had greater adherence to a Mediterranean diet pattern compared with the overall sample. Therefore, the divergent results for each type of tea were not confounded by the overall dietary pattern. In addition, prevalence of hypercholesterolemia and other cardiometabolic risk factors were not different between the types of tea. As such, it is plausible that green tea could be considered as a proxy for an overall healthier lifestyle in this population, and the results may be confounded by healthy user bias in green tea consumers, leading to a higher rating of the SAI. In particular, physical activity represents a potential confounding variable as it indicates green tea drinkers may be more health conscious, however, the green tea group also contained more smokers compared with black tea group, although the difference was not statistically significant.

Importantly, when proposing potential beneficial health effects of tea (and tea beverages) the quantity and the stability of the tea catechins (and other compounds) during the consumption and preparation of the beverages must be considered. From this perspective, temperature and exposure time (brewing time) pose an essential role in the stability of the tea components [ 58 ] as much as the quality of the water used in the preparation of a tea [ 59 ] and the repeated use of water during the tea preparation [ 60 ]. The latter is more prevalent (and somewhat exclusive) in Asian societies, making it very hard to count accurately the number of cups as a delivery method of tea flavanols (catechins) as the measure of exposure.

healthy ’ foods such as green tea. The FFQ could not evaluate the main catechins, polymerized polyphenols, and amino acid compositions in the observed teas. Therefore, the direct effects of these constituents cannot be readily established. However, adherence to a Mediterranean style dietary pattern was similar in both green and black tea drinkers, strengthening the findings of benefits due to green tea consumption. Another limitation of the analysis is both consumers of green and black tea scored lower on the SAI than the overall population sample which may be related to the higher age of both tea drinking groups. Higher percentages of hypertension, diabetes, and hypercholesterolemia were also observed in the tea drinking groups, which may also be contributing to the lower SAI score compared with the overall sample. To our knowledge, this is one of the first studies to investigate the consumption of green and black tea, and tea overall, in the Mediterranean region in relation to the successful ageing of the older adults. Two large population-based samples were analyzed in combination, reducing the potential for bias and increasing the external validity of the findings. A strength of the study is also the adjustment for confounding based on coffee consumption. The effects of coffee on overall health are relatively controversial but have been associated with lower all-cause mortality [ 61 ]. Nevertheless, this study has several limitations. Dietary habits and participants data were only measured through one food frequency questionnaires (FFQ) with potential for bias towards an inaccurate recall of food intake or tendency to over-report ‘’ foods such as green tea. The FFQ could not evaluate the main catechins, polymerized polyphenols, and amino acid compositions in the observed teas. Therefore, the direct effects of these constituents cannot be readily established. However, adherence to a Mediterranean style dietary pattern was similar in both green and black tea drinkers, strengthening the findings of benefits due to green tea consumption. Another limitation of the analysis is both consumers of green and black tea scored lower on the SAI than the overall population sample which may be related to the higher age of both tea drinking groups. Higher percentages of hypertension, diabetes, and hypercholesterolemia were also observed in the tea drinking groups, which may also be contributing to the lower SAI score compared with the overall sample.