Review
Tea, obesity, and diabetes
Yung-Hsi Kao, Hsin-Huei Chang, Meng-Jung Lee and Chia-Lin Chen
Department of Life Science, College of Science, National Central University, Chung-Li City, Taoyuan,
Taiwan
Discussion [...]
However, the absorption
and distribution of administrated EGCG and other tea catechins
are poor and dependent on catechin structure, purity,
dosage, the route of administration, and the tissue involved.
For example, after consumption of 1.5 g of decaffeinated
green tea solids, the catechins in human plasma reached
peak levels in 1.5–2.5 h [149]. At that time, the plasma
levels (free and conjugated) of EGCG, EGC, and EC levels
were 0.26, 0.48, and 0.19 lM, respectively, while ECG was
not detected [149]. Consumption of a single high dose of
green tea, equivalent to six cups of tea, can raise plasma
levels of catechin to 2–4 lM in 60 min [150]. [...]
Unfortunately, what is not clear at this time is whether
effective doses of catechins can be achieved in adipose tissues
simply by consuming tea infusions. Accordingly, the
doses of EGCG (
the effective dose of most studies is in the
range of 10–100 lM) or other tea catechins generally discussed
as above compatible with the goal of helping regulating
the initiation and progression of obesity and diabetes
are a little bit higher, but may be acceptable for the physiological
effect of EGCG in animals.
Conclusion [...]
Many benefits of tea have received great attention, but it is
also necessary to consider the adverse effects that may
accompany heavy use of tea or catechins. For example, high
doses of EGCG are reported to act as prooxidants, which
can lead to normal cell apoptosis [8, 17]. Thus, a further formulation
of EGCG or green tea polyphenols designed to
improve their
low bioavailability in vivo is required to
reduce their administered amounts by which experimental
models and clinical subjects keep the beneficial effects of
EGCG and tea polyphenols away from these adverse
effects. Several studies using whole tea or tea extract to
show the beneficial effects of green, oolong, and black teas
suggest that other ingredients of tea should be also considered
in making the inclusions of the formulation. Taken
together, the mechanistic results of this reviewmay possibly
be utilized in the treatment of obesity, diabetes, and other
related diseases using tea- and EGCG-based folk medicines.
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