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Asia Pac J Clin Nutr 2017;26(1):59-64 59
Original Article
Black tea consumption improves postprandial glycemic
control in normal and pre-diabetic subjects:
a randomized, double-blind, placebo-controlled
crossover study
Arisa Butacnum MSc, Rewadee Chongsuwat PhD, Akkarach Bumrungpert PhD
Department of Nutrition, Faculty of Public Health, Mahidol University, Bangkok, Thailand
Background and Objectives: Postprandial glycemic control is important for prevention of diabetes. Black tea
consumption may improve postprandial glycemic control. The major bioactive compounds are polyphenols, black
tea polymerized polyphenol (BTPP).This study examined the effect of black tea consumption on postprandial
blood glucose and insulin response following sucrose loading in normal and pre-diabetes subjects. Methods and
Study Design: This study was a randomized, double-blind, placebo-controlled crossover study. Twenty-four sub-
jects, male and female aged 20-60 years, normal and pre-diabetic, randomly ingested a sucrose solution with a
low dose (110 mg BTPP), a high dose (220 mg BTPP) of black tea drink or a placebo drink (0 mg BTPP). Blood
samples were collected at 0, 30, 60, 90, and 120 min from commencement of drink ingestion to measure blood
glucose and insulin levels. Results: The drink containing low dose and high dose BTPP significantly decreased
incremental blood glucose area under the curve (AUC) after sucrose intake compared with placebo in the normal
(T0-60 min 3,232±356 vs 3,295±312 vs 3,652±454 mg.min/dL; p=0.016) and pre-diabetic subjects (T0-60 min
2,554±395 vs 2,472±280 vs 2,888±502 mg.min/dL; p=0.048). There was no statistically significant difference of
changes in insulin levels between the placebo and black tea groups (p>0.05). No significant differences in adverse
effects were observed with the placebo, low dose and high dose of BTPP groups. Conclusion: Black tea con-
sumption can decrease postprandial blood glucose after sucrose intake.
Key Words: glycemic control, diabetes, black tea, black tea polymerized polyphenols, catechins
INTRODUCTION
Current epidemiology has estimated that the prevalence
of diabetes is increasing rapidly with significant medical
and economic consequences.1 The global prevalence of
diabetes was 171 million people in the year 2000, and it is
projected to increase to 366 million by 2030. The disease
is accompanied by high costs mainly due to chronic com-
plications. Diabetes and its complications have many
negative effects for health. Cardiovascular disease (CVD)
is the most common.
Postprandial glycemic control is important for preven-
tion of diabetes and/or delay of its complications. Moreo-
ver, the postprandial hyperglycemia in diabetic patients is
a more powerful marker of cardiovascular disease risk
than fasting hyperglycemia.2 Several experimental studies
provide a plausible pathophysiological explanation for
epidemiological data and give strength to the idea that
postprandial hyperglycemia is harmful.
The easiest way to prevent hyperglycemia is to control
blood glucose level in the normal range. Management
concentrates on keeping blood sugar levels as close to
normal as possible, without causing hypoglycemia. This
can usually be accomplished with diet, exercise, and use
of appropriate medications. Nevertheless prevention and
treatment of diabetes are not only available with conven-
tional medicine but also with alternative medicine. Func-
tional foods and nutritional supplements are promising
alternative medicines which have been used for regulation
of plasma glucose to prevent diabetes in order to save
costs for treatment of diabetes and complications.
Black tea is produced from the fresh leaves of Camellia
sinensis. It is one of the most widely consumed beverages
in the world. During the oxidation process, polyphenols
present in the tea leaf, the catechins, are enzymatically
converted to numerous polymerized polyphenols includ-
ing theaflavins and thearubigens.3 The major bioactive
compounds of black tea areblack tea polymerized poly-
phenol (BTPP).4 The health benefits of black tea poly-
phenols include anti-oxidant,4-6 anti-inflammatory,6-8 anti-
cancer,9,10 and anti-h ypertensive effects.11, 12 Moreover,
invitro studies suggest that extracts of black tea could
Corresponding Author: Dr Akkarach Bumrungpert, Depart-
ment of Nutrition, Faculty of Public Health, Mahidol Universi-
ty, 420/1 Rajvithi Road, Ratchathewi District, Bangkok 10400,
Thailand.
Tel: (+66) 2644-6842 Ext. 1205, (+66) 2354-8539
Email: abnutrition@yahoo.com; akkarach.bum@mahidol.ac.th
Manuscript received 03 September 2015. Initial review com-
pleted 13 September 2015. Revision accepted 18 October 2015.
doi: 10.6133/apjcn.112015.08
60 A Butacnum, R Chongsuwat and A Bumrungpert
interfere with carbohydrate absorption via their ability to
inhibit α-amylase, α-glucosidase, and sodium-glucose
transporters.13-16 Also, an animal study has shown the
suppressive effect of black tea polymerized polyphenol
on postprandial blood glucose in mice (unpublished).
Zhong et al found that the black tea extract induced mal-
absorption of 25% of the carbohydrate in healthy adult
human volunteers.17 Furthermore, Bryans et al established
that black tea decreases plasma glucose response in
healthy humans with a corresponding increase in insulin
level.18 However, there has been little clinical research on
the effects of black tea on postprandial glycemic control
and the results are not clear, especially in humans. There-
fore, our primary objective was to study the effect of
black tea consumption on postprandial blood glucose af-
ter sucrose loading in normal and pre-diabetic subjects.
MATERIALS and METHODS
The study was approved by the Ethical Review Commit-
tee for Human Research, Faculty of Public Health, Mahi-
dol University (MUPH 2014-145). Furthermore, this
study was conducted in accordance with the Declaration
of Helsinki on human subjects.
Subjects
We conducted a study in subjects with different back-
grounds by selecting normal subjects and pre-diabetic
subjects in order to ascertain the suppressive effect of the
black tea on sugar absorption. Twenty-four subjects aged
20-60 years were recruited at the Department of Nutrition,
Faculty of Public Health, Mahidol University. The inclu-
sion criterion for the normal group was fasting blood glu-
cose level of 70 to 100 mg/dL, pre-diabetic group was
fasting blood glucose level of 100-125 mg/dL. Subjects
had no diabetes, kidney or liver disease. Subjects who
were smokers, pregnant or nursing, regular users of a
pharmaceutical or food supplement that impacts glucose
metabolism were excluded. Also subjects were excluded
if they drank more than three cups daily of tea. Subjects
voluntarily participated in the study and provided written
informed consent.
Study materials
Menu set
The dinner for the day before the test day was prepared
by research assistants. The dinner consisted of rice,
minced fish dip with vegetables and rib soup, with energy
distribution carbohydrate 57%, protein 13%, and fat 30%.
Beverages
The test drink and placebo drink were manufactured by
Suntory Beverage & Food Limited (Japan). The composi-
tion of the test drinks and placebo drink are shown in Ta-
ble 1. Black tea drink was produced by extraction of
black tea leaves by hot water, and removing caffeine and
catechins. There were 2 doses of black tea drinks, low
dose (110 g BTPP) and high dose (220 g BTPP). Placebo
drink contained water and caramel coloring. The test
drink and placebo drink were packaged in cans.
Study design
This study design was a randomized, double-blind, place-
bo-controlled, crossover trial. The study consisted of one
baseline visit on the screening day and three visits on the
test day. Twenty-four subjects were selected from 72
candidates by a screening test and physical examination.
Blood pressure was measured by nurse after at least 5 min
of seated rest in a chair. Subjects were allocated to differ-
ent groups by the allocation manager based on their sex
and fasting glucose values. A total of 24 subjects were
randomly assigned into 2 major groups, normal and pre-
diabetic. There were 13 normal subjects (7 men and 6
women) and 11 pre-diabetic subjects (5 men and 6 wom-
en). Then subjects were randomly divided again to 3 mi-
nor groups for each test drink: a drink containing low
dose (110 g BTPP), a drink containing high dose (220 g
BTPP) and a placebo drink (0 g BTPP). Subjects con-
sumed the test drink with a 50 g sucrose solution (200
mL) prepared separately on each study day.
On the day before the study day, subjects abstained
from excessive eating and consumed the dinner specified
by the researcher. The specified dinner was picked up by
the subjects themselves from the Department of Nutrition,
Faculty of Public Health, Mahidol University. Alcohol
consumption was prohibited on the day before the study,
and the consumption of all foods and drinks except water
was also prohibited after 9 pm. Physical exercise was also
prohibited. Subjects reported to the study institution in a
fasting state. Then, a blood sample was collected from the
subjects at 0 min before sucrose loading. After that, the
beverage given to the treatment group was black tea drink
(500 mL) containing 110 mg of BTPP or 220 mg of
BTPP while the control group was given a placebo drink.
Then, each subject from the 3 groups was asked to ingest
50 grams of sucrose solution (200 mL) within 5 min.
Subsequently, subjects rested in the examination room
and blood was collected at 30, 60, 90, and 120 minutes
after sucrose loading (blood sample volume, 3 mL each).
Table 1. The composition of the test drinks and placebo drink
Nutritional content Test drinks (500 mL) Placebo drink (500 mL)
Low dose BTPP High dose BTPP
Energy (kcal) 0 0 0
Carbohydrates (g) ND ND ND
Fat (g) ND ND ND
Protein (g) ND ND ND
Sodium (mg) ND ND ND
Caffeine (mg) 0 0 0
BTPP (mg) 110 220 0
ND: Not detectable (<0.1 g/100 mL).
Black tea improves postprandial glycemic control 61
The plasma was separated from the samples and used to
measure blood glucose and insulin levels.
After the experiment, all subjects were asked to keep a
diary of severity of abdominal and other symptoms to
monitor the effect of the beverages they received. All
subjects were tested with the other groups as cross-over
study. Each participant received all treatments on the
same day of the week and had a 1 week washout period
between treatments: low dose BTPP, high dose BTPP and
placebo drink. This included result measurements and
monitoring of adverse events.
Analyses of blood samples
The following parameters were measured for screening
test and general characteristic of subjects: serum total
cholesterol (TC), low-density lipoprotein cholesterol
(LDL-C), high-density lipoprotein cholesterol (HDL-C),
triglycerides (TG), fasting blood glucose (FBG), HbA1C,
insulin, hemoglobin (Hb), hematocrit (Hct), serum glu-
tamic oxaloacetic transaminase (SGOT), serum glutamic
pyruvic transaminase (SGPT), alkaline phosphatase
(ALP), gamma-glutamyl transpeptidase (-GTP), uric
acid, blood urea nitrogen (BUN), creatinine, bilirubin,
lactate dehydrogenase, and creatine kinase. All bi-
omarkers were measured at N-Health Asia Lab, Thailand,
a medical laboratory with ISO15189:2007 certification.
Statistical analysis
The data were presented as mean±SD. Statistical differ-
ences of the means of incremental blood glucose AUC
and incremental blood insulin between the treatment and
the placebo groups were tested by one-way ANOVA and
post-hoc (Tukey) analysis. The adverse symptoms were
compared between ingestion of black tea and placebo
using one-way ANOVA. The levels of significance were
set to p<0.05.
RESULTS
Characteristics of subjects at baseline
Twenty four volunteers (13 normal subjects; 7 men, 6
women and 11 pre-diabetic subjects; 5 men, 6 women)
were recruited for the study. The mean ages of normal
and pre-diabetic subjects were 33.9 and 44.6 years, the
average BMI were 25.0 and 28.7 kg/m2, and mean glu-
cose levels were 89.9 and 108 mg/dL, respectively. Other
biochemical markers are shown in Table 2. All the sub-
jects were able to follow the study protocol and finish the
study.
Postprandial glucose and insulin response
The effect of the black tea on blood glucose and insu-
lin levels after sucrose loading in normal subjects
The postprandial responses in the blood glucose levels
following the ingestion of sucrose with the black tea drink
containing BTPP (low dose) significantly decreased in-
cremental blood glucose area under the curve (AUC) after
sucrose intake at 60, 90 and 120 mins compared with pla-
cebo (Figure 1A). Likewise, the BTPP (high dose) signif-
icantly suppressed the postprandial elevation in incremen-
tal blood glucose area under the curve (AUC) at 90 and
120 mins compared with placebo (Figure 1A). Moreover,
the incremental blood glucose after the intake of sucrose
with the black tea drink containing BTPP (low dose) was
significantly decreased at 60 min (91.4±8.19 vs 101±13.3
mg/dL) and 120 min (3.15±4.30 vs 9.46±3.93 mg/dL)
compared with placebo. Also, the incremental blood glu-
Table 2. General characteristic and blood chemistry of subjects
General characteristic and biochemical parameters Normal Pre-diabetic
Total number, men/women (n) 13 (7/6) 11 (5/6)
Age (years) 33.9±9.24 44.6±10.3
BMI (kg/m
2
) 25.0±3.72 28.7±5.56
Body fat (%) 27.8±7.59 33.9±7.85
Waist circumference (cm) 83.8±8.65 94.1±10.2
Systolic blood pressure (mm Hg) 125±8.77 1230±10.3
Diastolic blood pressure (mm Hg) 78.5±7.24 80.6±3.75
Pulse rate (beat/min) 76.7±8.23 75.9±6.95
Total cholesterol (mg/dL) 216±39.9 244±52.9
LDL-C (mg/dL) 154±32.7 151±30.9
HDL-C (mg/dL) 52.9±9.94 60.6±16.4
Triglyceride (mg/dL) 114±43.0 153±68.4
FBG (mg/dL) 89.9±3.36 108±6.48
HbA1C (%) 5.36±0.18 5.88±0.38
Insulin (
IU/mL) 5.36±3.92 10.2±4.30
Hb (g/dL) 14.3±1.54 13.7±1.73
Hct (%) 43.1±4.22 42.2±3.74
SGOT (U/L) 19.9±7.16 18.8±6.63
SGPT (U/L) 24.2±12.9 22.1±13.0
ALP (U/L) 61.4±14.3 64.8±9.34
-GTP (U/L) 32.4±31.4 48.9±33.1
Uric acid (mg/dL) 4.88±1.15 6.07±1.69
BUN (mg/dL) 10.3±2.23 11.3±2.81
Creatinine (mg/dL) 0.75±0.14 0.79±0.13
Bilirubin (mg/dL) 0.44±0.10 0.48±0.12
Lactate dehydrogenase (U/L) 162±17.5 172±32.53
Creatine kinase (U/L) 112±35.4 110±55.1
62 A Butacnum, R Chongsuwat and A Bumrungpert
cose after the intake of sucrose with the black tea drink
containing BTPP (high dose) was significantly decreased
at 60 min (90.3±9.94 vs 101±13.3 mg/dL) and 120 min
(2.46±3.07 vs 9.46±3.93 mg/dL) compared with placebo.
These results indicated that the black tea drink containing
BTPP could decrease postprandial blood glucose after
sucrose intake in normal subjects. There were no signifi-
cant differences between low dose and high dose of BTPP.
The postprandial responses in the blood insulin levels
following the ingestion of sucrose with or without black
tea drink containing the BTPP (low dose and high dose)
in normal subjects was not statistically significant differ-
ent between placebo, low dose and high dose of BTPP
groups (Figure 2A).
The effect of the black tea on blood glucose and insu-
lin levels after sucrose loading in pre-diabetic subjects
The postprandial responses in the blood glucose levels
following the ingestion of sucrose with the black tea drink
containing BTPP (low dose and high dose) significantly
decreased incremental blood glucose area under the curve
(AUC) after sucrose intake at 60 and 90 min compared
with placebo (Figure 1B). These results indicated that the
black tea drink containing BTPP could decrease post-
prandial blood glucose after sucrose intake in pre-diabetic
subjects. There was no significant difference in effect
between low dose and high dose of BTPP.
The postprandial responses in the blood insulin levels
following the ingestion of sucrose with or without black
tea drink containing the BTPP (low dose and high dose)
in pre-diabetic subjects were not statistically significantly
different between placebo, low dose and high dose of
BTPP groups (Figure 2B).
Adverse effects
Adverse events were assessed for any symptom in the
placebo, low dose and high dose of BTPP groups. They
were rare and no significant differences between the
groups.
DISCUSSION
In this study, we determined the extent to which BTPP
decreased the postprandial elevation in blood glucose
after sucrose intake in normal and pre-diabetic subjects.
We demonstrated that black tea reduced the incremental
blood glucose after sucrose consumption. This is con-
sistent with a previous study which showed that black tea
decreased the plasma glucose r esponse in healthy hu-
mans.17
A possible mechanism of action by which BTPP sup-
(A)
(B)
Figure 1. Effect of the black tea consumption on blood glucose levels after sucrose loading in normal and pre-diabetic subjects. (A)
Incremental b lood glucose AUC after sucrose loading in normal subjects. (B) Incremental blood glucose AUC after sucrose loading in
pre-diabetic subjects. a-b Values with different superscripts are significantly different from each other (p<0.05).
Black tea improves postprandial glycemic control 63
presses elevation of postprandial blood glucose after su-
crose intake is blocking carbohydrate absorption.16 In
vitro studies found that extracts of black tea interfere with
carbohydrate absorption via their abilities to inhibit α-
amylase,12,13 α-glucosidase14 and sodium glucose trans-
porter15 The abilities are similar to those found by Adi-
sakwattana et al19 who demonstrated that cinnamon bark
extracts may be potentially useful for the control of post-
prandial glucose in patients with diabetes through the
ability to inhibit of intestinal α-glucosidase and pancreatic
α-amylase. Likewise, Beejmohun et al20 demonstrated
that cinnamon extract significantly reduced the glycemic
response also in in vitro and in vivo studies by inhibiting
α-amylase activity. They found that 1 g of cinnamon ex-
tract reduced the AUC of glycemia at 0-60 mins (p<0.05)
compared with placebo, but cinnamon extract has no ef-
fect on insulin level. This efficacy of cinnamon for reduc-
tion of postprandial hyperglycemia but not change in in-
sulin level showed the same result as the consumption of
black tea in this study.
Moreover, the result of black tea consumption in this
study is similar to that of Zhong et al.17 They found the
mechanism of black tea extract is its ability to cause car-
bohydrate malabsorption. The conclusion from their study
was that the consumption of black tea extract induced
malabsorption of carbohydrate absorption by 25%.
Based on these findings it is suggested that black tea
inhibited carbohydrate absorption. On the other hand, the
effect of black tea on insulin sensitivity is still inconclu-
sive, since in this study there was no significant differ-
ence in the effects of black tea on insulin sensitivity.
However, the study of Bryans et al18 found black tea re-
duced the late phase plasma glucose response in healthy
humans with a corresponding increase in insulin.
Furthermore, the adverse events and the severity of
symptoms reported by the subjects for the 8 hrs of study
showed no significant differences in symptoms for the
placebo, low dose and high dose of BTPP groups. Never-
theless, some normal subjects drinking the high dose of
BTPP had nausea that may have been due to their fasting
overnight and the taste of black tea.
Based on our result and previously published data, we
have shown that BTPP can decrease postprandial glucose
after sucrose intake. The drinks containing BTPP might
inhibit α-amylase, α-glucosidase, and sodium-glucose
transporters activity resulting in block of carbohydrate
absorption causing decreased postprandial blood glucose.
Our findings suggest that ingestion of black tea with food
containing sugar is beneficial in glycemic control and
diabetic prevention.
Conclusion
The consumption of black tea containing BTPP can de-
crease postprandial blood glucose after sucrose intake in
both normal subjects and pre-diabetes subjects, suggest-
ing that black tea may be a promising anti-diabetic agent
for glycemic control.
(A)
(B)
Figure 2. Effect of the black tea consumption on blood insulin levels after sucrose loading in normal and pre-diabetic subjects. (A) In-
cremental blood insulin after sucrose loading in normal subjects. (B) Incremental blood insulin after sucrose loading in pre-diabetic sub-
jects. No statistically significant difference between groups.
64 A Butacnum, R Chongsuwat and A Bumrungpert
ACKNOWLEDGEMENT
The authors thank Assoc. Prof Dr Harold C Furr, Department of
Nutrition, University of Wisconsin, Madison, USA for reading
and editing the final manuscript. This study was funded by Sun-
tory Beverage & Food Limited (Japan).
AUTHOR DISCLOSURES
The authors declare no conflict of interest regarding this paper.
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