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- Rooibos Tea (Aspalathus linearis)
- Antioxidant Capacity
- Total Radical-trapping Antioxidant Potential (TRAP)
| Date:
01-31-2011 | HC# 091062-417
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Re: Rooibos Tea Consumption Acutely Increases Plasma Antioxidant Capacity in Healthy Subjects
Villano D,
Pecorari M, Testa M, et al. Unfermented and fermented rooibos teas (Aspalathus linearis) increase plasma
total antioxidant capacity in healthy humans. Food Chem. 2010;123(3):679-683.
Pre-clinical
studies have shown that rooibos (Aspalathus
linearis) tea possesses antioxidant effects.1 This antioxidant
activity has been primarily attributed to polyphenolic constituents that
include the unusual compounds aspalathin and nothofagin, as well as caffeic
acid, protocatechuic acid, quercetin, rutin, isoquercitrin, and others.1
Fermentation of rooibos tea oxidizes many of these polyphenolic compounds. This
randomized, placebo-controlled, crossover, clinical study was the first to
assess the antioxidant capacity of both fermented and unfermented rooibos tea
in healthy human subjects.
Beverage
Partners Worldwide (Zurich,
Switzerland)
provided 500 mL bottles of fermented and unfermented rooibos teas containing
1.5 g/L rooibos extract powder for the study. The authors recruited 15 healthy
nonsmokers who did not take medications or antioxidant supplements. For 2 days
prior to the study, the subjects followed a low-antioxidant diet that excluded fresh
fruits and vegetables, tea, coffee, and wine. The subjects kept dietary records
to ensure that they did not consume high-antioxidant foods and beverages. The
subjects were randomized into 3 groups (randomization method not stated): group
A received 500 mL water (control), group B received 500 mL fermented rooibos
tea, and group C received 500 mL unfermented rooibos tea. Venous blood samples
were collected 0, 0.5, 1, 2, and 5 hours after the subjects drank the tea.
Following 2-week wash-out periods, the subjects were crossed over to the other
treatments until all patients had received all treatments. The researchers
measured the total antioxidant capacity (TAC) of the subjects' plasma and the
teas using the total radical-trapping antioxidant potential (TRAP) assay. In
addition, they measured the subjects' levels of plasma glucose, total
cholesterol, triglycerides, and urate.
The in
vitro results showed that unfermented rooibos tea has a 28% higher TAC than fermented
rooibos tea (unfermented: 5.23 ± 0.80 mmol/L; fermented: 4.07 ± 0.29 mmol/L).
The authors comment that both fermented and unfermented rooibos teas
"possess a lower chain-breaking antioxidant potential than do green and
black teas [Camellia sinensis] but
higher than commercially available instant tea."
There were
no significant changes in the subjects' plasma triglyceride, uric acid, or
total cholesterol levels. Their plasma glucose levels increased significantly compared
to baseline 30 minutes after drinking the fermented and unfermented rooibos
teas (fermented: +32.0%, P<0.001; unfermented: +21.6%, P<0.001), but not
water. The authors do not provide information about product formulation, but
this increase could be due to sweetener added to the teas. Water did not affect
the subjects' plasma TRAP values. Plasma TRAP values increased compared to
baseline 30 minutes after the subjects drank the fermented rooibos tea (+4.8%),
and the increase was statistically significant 1 hour post-ingestion (+6.6%, P<0.05
compared to baseline and control). The subjects' plasma TRAP values increased
30 minutes after drinking the unfermented rooibos tea (+1.7%), and the
difference was statistically significantly higher than the control 1 hour (+2.9%,
P<0.01) and 2 hours post-ingestion (+2.7%, P<0.05). Although still
significantly higher than baseline values, the subjects' plasma TRAP values
started to decline at 2 hours post-ingestion (+4.9%, P<0.05 compared to
baseline). The subjects' plasma TRAP values returned to baseline levels 5 hours
after ingestion. The authors failed to mention the presence or absence of
adverse side effects. No withdrawals from the study were reported.
This is the
first clinical study to show that rooibos tea acutely increases plasma
antioxidant levels in human subjects. It is interesting to note that, while the
unfermented rooibos tea showed a greater antioxidant capacity compared to the
fermented tea in vitro, the in vivo results show that fermented tea has greater
effect on plasma TRAP values compared to the unfermented rooibos tea. This
raises questions about bioavailability. Further clinical studies to confirm
these results and to examine the effect of chronic rooibos tea consumption on
antioxidant status are warranted
—Marissa Oppel-Sutter, MS
Reference
1. Milot
B. Comprehensive review of rooibos. HerbClip.
February 27, 2004 (No. 100331-251). Austin,
TX: American Botanical Council.
Review of Rooibos tea: research into antioxidant and antimutagenic properties
by Erickson L. HerbalGram. 2003;59:34-45.
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