Antioxidant-rich extracts from green tea may reduce the effects of oxidative stress caused by breathing problems while people are sleeping, according to US researchers.
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