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| Date: 05-15-2015 | HC# 111436-520 |
Re: Green Tea and Hibiscus (Sour Tea) Consumption Improves Insulin Resistance and HDL-C Levels in Patients with Type 2 Diabetes
Mozaffari-Khosravi
H, Ahadi Z, Fallah Tafti M. The effect of green tea versus sour tea on insulin
resistance, lipids profiles and oxidative stress in patients with type 2
diabetes mellitus: a randomized clinical trial. Iran J Med Sci. 2014;39(5):424-432.
Diabetes
mellitus (DM) is the most common chronic metabolic disease worldwide.1,2
Clinical trials have shown that oxidative stress is involved in the development
of complications of the disease. Decreasing oxidative stress and insulin
resistance might lower the incidence and severity of those complications. Green
tea (Camellia sinensis, Theaceae) leaf
and hibiscus (sour tea; Hibiscus
sabdariffa, Malvaceae) calyces both contain flavonoids and various
polyphenols that have antioxidative and anti-inflammatory properties. The goal
of this randomized, controlled trial was to compare the effects of hibiscus tea
and green tea on insulin resistance, lipid profiles, and oxidative stress in
patients with type 2 diabetes.
The
study was conducted at the Yazd Diabetic Research Centre at the Faculty of
Health at Shahid Sadoughi University of Medical Sciences in Yazd, Iran, during
2011-2012. Patients were nonsmokers, aged 30-60 years, with a fasting blood
sugar (FBS) between 80 and 250 mg/dL. They had no obvious diabetes
complications, no history of using dietary supplements during the preceding 6
months, and no history of organ disease. All had diabetes for a minimum of 5 years
and were non-insulin dependent.
The
100 eligible patients were randomly assigned into either a green tea (GT) or hibiscus
tea (ST) group, with 50 in each group. All patients were given a specified
number of labeled tea packets, advised to prepare the tea at home according to
instructions, and instructed to drink 150 mL tea 3 times daily (2 hours after
meals) for 4 weeks. No information regarding either tea is provided in the
article. The patients were asked to follow these additional guidelines – drink
the entire 150 mL of tea, avoid drinking any other kind of tea during the trial,
and continue their usual physical activity and daily diet, excluding foods
containing polyphenols such as chocolate (Theobroma
cacao, Malvaceae) and coffee (Coffea
spp., Rubiaceae).
During
the trial, patients were asked about allergic reactions or adverse side effects
caused by the tea. Compliance was determined by the percent of unused teabags.
At
baseline and after 4 weeks, demographic, anthropometric, and 24-hour dietary
recall data were measured. Overnight fasting blood samples were drawn to
measure FBS, fructosamine, triglycerides, total cholesterol, high-density
lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C),
fasting blood insulin, and serum malondialdehyde (MDA). Insulin resistance was
assessed using the homeostasis model assessment of insulin resistance
(HOMA-IR), the level of beta-cell function (b%), and insulin sensitivity (S%).
Of
the 100 patients, 94 completed the trial. Four patients in the ST and 2 in the GT
groups dropped out because of allergy to the specified tea, reluctance to
continue in the clinical trial, travel, and/or being unable to tolerate the
taste of the tea. Compliance rates were 89% in the ST and 91% in the GT groups.
The
authors report that the mean FBS, fructosamine, triglycerides, total
cholesterol, LCL-C, and MDA levels did not change significantly within or
between the groups during the trial. The mean HDL-C increased significantly in
both groups, but no between-group differences were noted before or after the
intervention.
Mean
S% showed no between-group differences at baseline but significant differences
were seen in the GT group (96 ± 45.3) compared with the ST group (70 ± 34.1) after
4 weeks (P=0.002). The mean S% before and after intervention showed no
significant difference in the GT group. However, in the ST group, a significant
decrease was seen compared with baseline values (P<0.001). Mean MDA levels
showed no between-group differences before or after the treatment.
The
median fasting insulin in the GT group decreased significantly (from 8.5 to 6.6
μIU/mL, P=0.04), but in the ST group, a significant increase (8.2 to 16.3 μIU/mL;
P<0.005) was observed. Although the between-group difference was not
significant at baseline, a significant difference was observed after 4 weeks
(P=0.005). The median HOMA-IR after 4 weeks in the GT group was lower than in
the ST group (1.1 vs 1.6; P=0.004). In the ST group, the median HOMA-IR index
increased significantly after 4 weeks of intervention (P=0.002). In the GT
group, no significant change was observed.
The
mean b% level increased significantly in the ST group (from 38.2% at baseline
to 47.7% at 4 weeks; P=0.023), but no significant changes were seen in the GT
group. The mean S% showed a significant decrease in the ST group but not in the
GT group after the intervention.
The
authors state that earlier studies have yielded conflicting results concerning
the effects of green and hibiscus teas on HDL-C and FBS. In this study,
drinking the hibiscus tea and green tea infusions 3 times daily for 4 weeks had
positive effects on insulin resistance and HDL-C levels in patients with type 2
diabetes. However, the authors admit that the study is limited by the short
test period and lack of a control group. They recommend additional studies be
carried out with a control group and longer consumption period.
—Shari Henson
References
1Shaw JE, Sicree RA,
Zimmet PZ. Global estimates of the prevalence of diabetes for 2010 and 2030. Diabetes Res Clin Pract. 2010;87(1):4-14.
2Azimi-Nezhad M,
Ghayour-Mobarhan M, Parizadeh MR, et al. Prevalence of type 2 diabetes mellitus
in Iran and its relationship with gender, urbanisation, education, marital
status and occupation. Singapore Med J.
2008;49(7):571-576.
