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- Green Tea (Camellia sinensis)
- Antioxidants
- Genoprotection
| Date:
12-15-2010 | HC# 111051-414
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Re: Genoprotective Effects of Green Tea
Han KC,
Wong WC, Benzie IFF. Genoprotective effects of green tea (Camellia sinensis) in human subjects: results of a controlled
supplementation trial. Br J Nutr.
Sept 1, 2010: 1-8 [Epub ahead of print].
Tea (Camellia sinensis), especially green
tea, is rich in polyphenolic antioxidants. The total antioxidant content of
human plasma increases significantly within 30 min of ingesting green tea. Whether
this effect relates to the modulation of oxidative stress in humans is unknown.
Also, the potential health benefit of this effect is unknown. Hence, the
purpose of this two-part study was to evaluate and compare the in vitro and clinical
effects of different concentrations of green tea on human lymphocytic DNA. The
specific teas (supplied by the Ying Kee Tea House, Hong Kong) were chosen based
on their regional (Hong Kong) popularity.
In Vitro Assessment
Infusions (1% w/v) of Longjing green
tea and screw-shaped green tea were infused in phosphate buffered saline (PBS) for
10 min and then filtered. Freshly prepared infusions were diluted in PBS to
give 0.1%, 0.05%, 0.01%, and 0.005% (w/v) tea solutions. The total antioxidant
content (as the ferric-reducing antioxidant power value) was measured.
Lymphocytes were pooled from the venous blood of 5 healthy volunteers. The
comet assay, most commonly performed on peripheral lymphocytes, was conducted.
The comet assay is often used to evaluate potential genoprotective or genotoxic
agents. It is used to study intervention-related changes in basal levels of
oxidation-induced DNA damage and resistance of DNA to oxidant challenge.
Both teas had similar total antioxidant
content. According to the comet assay, no detectable DNA damage was caused by
either tea at any concentration tested. Cells that were pretreated with tea
prior to an oxidant challenge had less DNA damage than cells not pretreated.
Both teas offered similar levels of protection. There was no dose-response
effect of the different concentrations of teas.
Clinical Assessment
Eighteen
healthy men and women (aged 35-50 years) participated in this single-blind,
crossover study conducted at The Hong Kong Polytechnic University, Kowloon, Hong Kong.
Subjects ingested 150 ml 1% (w/v) freshly prepared Longjing green tea,
screw-shaped green tea, or hot water (control) twice daily for 4 weeks.
Subjects made their own tea following a set of standardized instructions and
using the teabags and mugs provided. Subjects were non-smokers, without
hypertension, not on regular medication, and with no previous history of stroke,
myocardial infarction, angina, diabetes mellitus, cancer, or any illness that
had required hospitalization during the previous 12 months. At entry, 6 subjects
were allocated to each treatment. After a 6-week wash-out period, the subjects
crossed-over into 1 of the other 2 treatments. Then, following a second 6-week
washout, the subjects ingested the third treatment. By the end of the study,
all of the subjects had taken all 3 treatments. Compliance was assessed by
inquiry and by counting the number of returned tea bags at the end of each
intervention. Fasting venous blood and urine samples were collected before and
after each supplementation phase. Blood was tested with the comet assay and
urine was assayed for 7,8-dihydro-2-deoxyguanosine (8-oxodG). 8-oxodG is a
biomarker for whole-body oxidative stress.
According
to an oxidant challenge, cells collected from subjects after 4 weeks of tea
supplementation had 22% less DNA damage after oxidant challenge than cells
obtained after water ingestion (P < 0.05). According to the comet assay, DNA
damage was 30% less in cells collected after Longjing tea consumption and 35%
less after screw-shaped tea consumption compared with before consumption. This amount
of DNA damage was significantly less than the amount of DNA damage after water
treatment (P < 0.05). There were no significant differences in 8-oxodG. This
may be attributed to the high biological variability in urine 8-oxodG.
The authors
conclude that both types of tea provided significant genoprotection both in
vitro and clinically, and both teas had a similar magnitude of effect and total
antioxidant content. This implies that the genoprotective effects may be
generalizable to other green teas containing similar total antioxidant content.
The mechanism of action is unknown but may be related to the polyphenol
content. Unfortunately, the authors did not measure plasma polyphenol content.
A dietary
relevant dose of green tea was evaluated and produced a significant decrease in
oxidation-induced DNA damage and significant increase in DNA resistance to
oxidant challenge. Oxidation-induced DNA damage can cause cellular mutation, malignant
(cancerous) changes in cells, altered homeostasis, and apoptosis (programmed cell
death). This study supports the belief that green tea can promote health. The
study should be repeated with additional types of green tea.
—Heather S. Oliff, PhD
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