What’s your ZU-B?

The small study with 14 healthy adults found that the benefits of the beverage was not related to the caffeine, indicating the possible role of green tea polyphenols, previously linked to protection against certain kinds of cancers and Alzheimer’s.

The study is published in the European Journal of Cardiovascular Prevention and Rehabilitation.

“These findings have important clinical implications,” said study co-author Charalambos Vlachopoulos from Athens Medical School in Greece. “Tea consumption has been associated with reduced cardiovascular morbidity and mortality in several studies. Green tea is consumed less in the Western world than black tea, but it could be more beneficial because of the way it seems to improve endothelial function.

“In this same context, recent studies have also shown potent anticarcinogenic effects of green tea, attributed to its antioxidant properties,” added Dr Vlachopoulos.

Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea.

The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).

Study details

The Greek researchers randomly assigned the volunteers (average age 30) to one of three groups. The first receive six grams of green tea, the second received 125 mg of caffeine (equivalent to the caffeine dose from six grams of tea), and the third group received hot water.

The volunteers consumed each of the interventions on three separate occasions, and the effects on flow-mediated dilation (FMD), the measure of a blood vessel’s healthy ability to relax, measured 30, 90 and 120 minutes after consumption.

Green tea increased FMD by 3.9 per cent 30 minutes after consumption, while no changes in FMD were observed following consumption of caffeine or the hot water placebo.

“Green tea consumption has an acute beneficial effect on endothelial function, assessed with FMD of the brachial artery, in healthy individuals,” wrote the researchers.

“This may be involved in the beneficial effect of tea on cardiovascular risk,” they concluded.

Source: European Journal of Cardiovascular Prevention and Rehabilitation

Obstructive sleep apnea (OSA) occurs when people stop breathing while they are sleeping, often for a minute or more, and this may many hundreds of times during a single night’s sleep. It is usually caused when the soft tissue in the rear of the throat collapses and closes during sleep, according to the American Sleep Apnea Association.

As such, people with this disorder are said to be at risk of oxidative stress and exhibit changes in their brain tissue in areas involved in learning and memory.

Supplements of green tea extracts may counter the cognitive deficits that may occur, suggests a new study with rats, published in American Journal of Respiratory and Critical Care Medicine.

If the results of the study can be repeated in humans, green tea and its extracts may offer a potential interventional strategy for people with the disorder, reported to be in the region of 12 million or so people in the US, according to the National Institutes of Health.

“OSA has been increasingly recognized as a serious and frequent health condition with potential long-term morbidities that include learning and psychological disabilities,” wrote lead researcher David Gozal from the University of Louisville.

Study details

Human OSA was modelled in rats by intermittently depriving the animals of oxygen during 12-hour “night” cycles for 14 days - intermittent hypoxia (IH). The researchers divided the 106 male rats into two groups, with one group assigned to receive drinking water containing green tea polyphenols.

The University of Louisville researchers, in collaboration with scientists from Soroka University Medical Center, then tested the animals for markers of inflammation and oxidative stress, in addition to using a water maze to test their performance in spatial learning and memory tasks.

They report that rats that received the green tea polyphenol (GTP)-supplemented water performed significantly better in a water maze than the rats that drank plain water.

Moreover, levels of malondialdehyde (MDA), a reactive carbonyl compound and a well-established marker of oxidative stress, were 40 per cent lower in the GTP-supplemented animals, added the researchers.

“GTP-[supplemented] rats exposed to IH displayed significantly greater spatial bias for the previous hidden platform position, indicating that GTPs are capable of attenuating IH-induced spatial learning deficits,” wrote Gozal.

“Because oxidative processes underlie neurocognitive deficits associated with IH, the potential therapeutic role of GTP in sleep-disordered breathing deserves further exploration,” he added.

Antioxidant activity

The benefits of the green tea extracts were attributed to the antioxidant properties of green tea polyphenols. “Recent studies have demonstrated the neuroprotective activity of GTP in animal models of neurodegenerative conditions such as Parkinson’s and Alzheimer’s disease,” wrote Gozal.

Green tea is said to contain over four times the concentration of antioxidant catechins than black tea (green tea leaves that have been oxidized by fermentation), about 70 mg catechins per 100 mL compared to 15 mg per 100 mL for black tea.

The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.

Source: American Journal of Respiratory and Critical Care Medicine
Volume 177, Pages 1135-1141, doi:10.1164/rccm.200701-110OC
“Green Tea Catechin Polyphenols Attenuate Behavioral and Oxidative Responses to Intermittent Hypoxia”
Authors: I.C. Burckhardt, D. Gozal, E. Dayyat, Y. Cheng, R.C. Li, A.D. Goldbart, B.W. Row

The results add to an ever-growing body of science linking consumption to a wide range of health benefits, including lower risk of certain cancers, increased weight loss, improved heart health, and protection against Alzheimer’s.