Earning the green with tea

The green-tea market is branching out into many new health facets, including exercise, diabetes, cardiovascular health, cosmeceuticals and weight management. Mark J Tallon investigates the new and emerging science developing this botanical phenomenon into a truly diverse category

Great education and marketing behind green tea and its actives have made this product a real consumer favorite. Future applications and functionalities should maintain green tea and its most pharmacologically active constituent, EGCG, as hot commodities for some time to come.

Green tea and exercise
Green tea extract and EGCG have been shown to increase lipid oxidation rates and also to attenuate fat-mass gains.^1,2 UK researchers recently presented results of one of the first human studies utilising a standardised green-tea extract on fat oxidation during moderate-intensity exercise.

This study investigated 12 healthy males performing 30-minute cycling exercises at an intensity of 50 per cent of maximal power output. Participants took 388mg EGCG or a placebo. Results showed no change in caloric expenditure, though there was a significant (17 per cent) increase in fat oxidation as compared to those taking the placebo.

The suggested mechanism for this increase in 'fat burning' is via the inhibition of an enzyme (catechol O-methyl-transferase) that reduces the degradation of catecholamines. As catecholamines (adrenaline and noradrenaline) are integral to the drive behind fat use during exercise, any increase in its release should enhance fat use as a fuel.

One application of this research is to assess its influence, when added to energy drinks, to reduce the use of muscle glycogen (the body's carbohydrate store) during exercise. This increase in cellular glycogen would increase the ability to exercise for longer periods without fatigue.

Green tea and insulin response
Studies have shown that green tea as well as cocoa can influence the glucoregulatory response to glucose intake (ie, insulin release). However, no data exist regarding the action of both nutrients taken together or evidence of dose effects. Researchers from the Beltsville Human Nutrition Research Center recently investigated these issues by comparing the dose-response effect of both green tea and cocoa polyphenols (CP) on glucose and insulin response, following an oral glucose-tolerance test.³

Twenty subjects on a controlled diet were given one of five treatments: high-dose cocoa (900mg CP), medium-dose cocoa (400mg CP), low-dose cocoa (200mg CP), control cocoa (22mg CP), or green tea. Supplements were taken with breakfast and dinner for five days. A glucose-tolerance test was given on the sixth day.

The results showed that green tea, compared to high-dose cocoa, lowered glucose and insulin concentrations in normal, but not insulin-resistant, subjects.³

It would have been of interest to assess lipid responses between these two studies, as both these bioactives have been suggested to alter LDL levels.4^,5 Overall, this study shows additional benefits of green tea related to the control of insulin. However, in subjects who were insulin resistant, no beneficial effects of green tea were shown. Further work should examine the dose-response relationship of green tea on insulin levels.

Cardio health
Evidence is accumulating that shows an exaggerated post-prandial lipid response is associated with increased cardiovascular disease risk. At present a selection of studies exists showing green tea ameliorates raised plasma lipid levels. However, little data exists to show what influence green tea has on post-menopausal women, who have a significant decline in cardio-protective hormones such as oestrogen.

Researchers assessed the effect of a green-tea extract following a standardised fat load (crossover design, one-week wash-out). The fat load was given in a beverage containing 50g fat, 50g carbohydrate, 2g lyophilised green-tea extract and 50mg vitamin E.⁶ Following consumption of the load, plasma analysis over a six-hour period assessed changes in triglyceride and vitamin E levels.

The results: green-tea extract lowers the post-meal response to fat intake, determined by lower plasma triglycerides and chylomicron levels of triglycerides and vitamin E. The implications of reduced vitamin E levels are unknown, but may be related to an inhibited fat absorption post feeding. Although EGCG may decrease the appearance of plasma lipid levels, further work should assess long-term-use implications on fat-soluble vitamin levels.

Oxidative stress
The cosmeceuticals market has been suggested as one of the biggest opportunities to hit the Functional Ingredients markets in more than a decade. The principal focus has been on ways to defend the skin from free radicals, which when produced in excessive levels can accelerate signs of ageing.7 A study presented at the Experimental Biology conference (Washington, DC) took a further look at the issue of oxidative stress research. This study examined whether an acute green-tea dose (64.42mg EGCG) could influence resting metabolic rate, and, more importantly, oxidative stress as indicated by urinary markers (8-iso-prostaglandin-F2).8

Subjects were given six doses of tea over a 48-hour period. Compared to placebo, oxidative stress was significantly reduced based on 8-iso PGN-F2 levels.8 Although it was only a small-scale study with 22 subjects, the study provides a little more evidence that oral supplementation with green tea can reduce oxidative markers as found in topical applications trials. Further work is needed to assess if long-term green-tea supplementation can influence skin physiology at a cosmetic level.

Weight management
Multiple studies indicate the efficacy of green tea in its extracted solid-dose form.4^,9 When given as EGCG, the major bioactive linked to the enhanced release of catecholamines and subsequent weight loss, results are somewhat less convincing.

To date only one study has looked at EGCG supplementation in human subjects.¹⁰ In 2006, 38 post-menopausal women were given 300mg/day of a 98 per cent pure EGCG extract or placebo over a 12-week period while undertaking regular exercise (45 minutes, three times per week).

Following supplementation, there were no significant treatment effects on indices of body composition or body weight. EGCG appeared to increase fat oxidation during exercise, although not significantly. The study is interesting but again there are other factors here to take into consideration, such as menopause being associated with a decreased response to catecholamine release, the exact mechanism that EGCG is said to be affording its effects.^2,11 Therefore, a higher dose may be needed in this population if weight loss is to be achieved.

At the 2007 Vitafoods conference (Geneva, Switzerland), DSM presented results of a double-blind, randomised, placebo-controlled, crossover pilot trial involving 10 healthy but overweight/obese volunteers (BMI 27-35).¹ Subjects received supplements of either Teavigo (DSM's patented EGCG extract), caffeine, both, or placebo. Subjects were assigned to one of five supplementation dose groups: 300mg Teavigo, 600mg Teavigo, 200mg caffeine, 300mg Teavigo plus 200mg caffeine or placebo. The respiratory quotient (a measure of metabolism) of those receiving the 300mg EGCG supplement was more improved than for the 600mg-dose group. The data confirms in part some efficacy of EGCG in healthy populations.

More work is needed in this area directly related to weight loss and specific dosing patterns, and additional benefits when combined with other active compounds such as caffeine.12 Green tea, and indeed EGCG, are now opening up many novel opportunities including the cardioprotective (prevention of stroke13) and cosmeceuticals markets, the latter as a dermoprotectant against sun- or chemotherapeutically induced damage.14

Mark J Tallon, PhD, is chief science officer of OxygeniX (oxygenix.com), a London-based consultancy firm specialising in claims substantiation, product development and technical writing. Dr Tallon is also co-founder of Cr-Technologies (cr-technologies.net), a raw-ingredients supplier. Respond: [email protected]

References
1. Theo Graser, MD PhD. DSM Nutritional Products' innovative ingredients help to address the main health concerns. 2007, Vitafoods Conference, Geneva.
2. Venables MC, et al. Green tea extract increases fat oxidation during exercise in humans. FASEB online 2007; abstract 280.
3. Stote KS. Effect of cocoa and green tea consumption on glucoregulatory biomarkers in insulin resistant men and women. Faseb J 2007;21:847.17.
4. Nagao T, et al. A green tea extract high in catechins reduces body fat and cardiovascular risks in humans. Obesity 2007;15(6):1473-83.
5. Polagruto JA, et al. Cocoa flavanol-enriched snack bars containing phytosterols effectively lower total and low-density lipoprotein cholesterol levels. J Am Diet Assoc 2006;106(11):1804-13.
6. Vaishnav U, et al. Effect of green tea on postprandial lipidemia in postmenopausal women. FASEB online 2007; abstract 847.9.
7. Katiyar SK, et al. Polyphenolic antioxidant (-)-epigallocatechin-3-gallate from green tea reduces UVB-induced inflammatory responses and infiltration of leukocytes in human skin. Photochem Photobiol 1999;69(2):148-53.
8. McCune LM, et al. Short term effects of green tea on resting energy expenditure, oxidant stress and inflammation in overweight/obese, post-menopausal women. FASEB online 2007; abstract LB228.
9. Diepvens K, et al. Metabolic effects of green tea and of phases of weight loss. Physiol Behav 2006;87(1):185-91.
10. Howe P, et al. Cardiovascular and metabolic effects of epigallocatechin gallate (EGCG) supplementation in conjunction with an exercise program in overweight women. Obesity Rev 2006;7 (Suppl 2):310.
11. D'Eon TM, et al. Estrogen regulation of adiposity and fuel partitioning. Evidence of genomic and non-genomic regulation of lipogenic and oxidative pathways. J Biol Chem 2005;280:35983-91.
12. Westerterp-Plantenga MS, et al. Body weight loss and weight maintenance in relation to habitual caffeine intake and green tea supplementation. Obes Res 2005;13(7):1195-204.
13. Fraser ML, et al. Green tea and stroke prevention: emerging evidence. Complemen Ther Med 2007;15(1):46-53.
14. Pajonk F, et al. The effects of tea extracts on proinflammatory signaling. BMC Med 2006;1(4):28.