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ISSN: 0953-7104 (Print) 1369-1635 (Online) Journal homepage: http://www.tandfonline.com/loi/iplt20
Effects of kiwi fruit consumption on platelet
aggregation and plasma lipids in healthy human
Asim K. Duttaroy & Aud Jørgensen
To cite this article: Asim K. Duttaroy & Aud Jørgensen (2004) Effects of kiwi fruit consumption on
platelet aggregation and plasma lipids in healthy human volunteers, Platelets, 15:5, 287-292, DOI:
To link to this article: http://dx.doi.org/10.1080/09537100410001710290
Published online: 07 Jul 2009.
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Effects of kiwi fruit consumption on platelet
aggregation and plasma lipids in healthy human
Asim K. Duttaroy, Aud Jørgensen
Fruits and vegetables have been thought to be beneficial in cardiovascular disease. The beneficial effects of fruits
and vegetables may be explained by the antioxidants and other components contained therein. These nutrients may
function individually or in concert to protect lipoproteins and vascular cells from oxidation, or by other mechanisms
such as reducing plasma lipid levels (LDL cholesterol, triglycerides), and platelet aggregation response. Kiwi fruit
which contains high amounts of vitamin C, vitamin E and polyphenols may be beneficial in cardiovascular disease;
however very little is known about its cardioprotective effects. Platelets are involved in atherosclerotic disease
development and the reduction of platelet activity by medications reduces the incidence and severity of disease. To
this end, we evaluated whether consuming kiwi fruit modulated platelet activity and plasma lipids in human
volunteers in a randomized cross-over study. We report that consuming two or three kiwi fruit per day for 28 days
reduced platelet aggregation response to collagen and ADP by 18% compared with the controls (P<0.05). In
addition, consumption of kiwi fruit lowered blood triglycerides levels by 15% compared with control (P<0.05),
whereas no such effects were observed in the case of cholesterol levels. All these data indicate that consuming
kiwi fruit may be beneficial in cardiovascular disease.
Many risk factors for cardiovascular disease (CVD)
including platelet hyperactivity, high blood choles-
terol, triglycerides, obesity and diabetes are substan-
tially influenced by dietary factors. Since these risk
factors are modifiable therefore primary preventive
efforts through dietary means hold much promise.
High intake of fruit and vegetables is such an
important preventive measure by which the risk of
cardiovascular disease can be reduced. The American
Heart Association and other national agencies
recommend a diet that includes 5 servings of fruit
and vegetables daily.
These recommendations are
based primarily on the studies indicate that fruit and
vegetable intake may reduce CVD risk through the
beneficial combinations of micronutrients, antioxi-
dants, phytochemicals, and fiber in fruits and
A decreased oxidative modification of
LDL may be one of the mechanisms by which fruits
and vegetables reduce the risk of CVD and athero-
sclerotic progression. However, hyperactivity of
platelets, and their adhesion and aggregation at the
site of injury in atherosclerotic vessel walls, is also
critically important in the pathogenesis of CVD.
There is also an increasing evidence that acute clinical
manifestations of coronary atherosclerotic disease
are caused by plaque disruption and subsequent
sclerotic lesions may appear in early life and, towards
the end of the second decade of life, asymptomatic
atherosclerotic lesions are present in most people
living in industrialised societies.
let activity may play a major role in the development
as well as in the stability of atherosclerotic plaques.
In support of the pathophysiological role of platelets,
platelet inhibitory drugs such as aspirin reduce the
incidence of myocardial infarction, stroke and death
from CVD in secondary prevention trials.
Flavonoids are polyphenolic compounds, widely
distributed in fruit and vegetables, many of which
have antioxidant as well as anti-thrombotic proper-
Certain polyphenols have been shown to be
inhibitory to platelet aggregation than others, and
Asim K. Duttaroy, Aud Jørgensen, Department of Nutrition,
Faculty of Medicine, University of Oslo, Oslo, Norway.
Correspondence to: Professor Asim K. Duttaroy, Department of
Nutrition, University of Oslo, P.O. Box 1046 Blindern, N-0316
Oslo, Norway. Tel.: þ47-22-85-15-47; Fax: þ47-22-85-13-41;
Platelets (August 2004) 15(5), 287–292
ISSN 0953-7104 print/ISSN 1369-1635 online/04/050287-6 ß2004 Taylor & Francis Ltd
consequently dietary studies involving flavonoids
on anti-platelet effects are not conclusive.
difference in platelet inhibitory effects among poly-
phenols could be due to several reasons. Variations in
digestion, absorption, and hepatic processing may
limit the bioavailability of these compounds. It is also
possible that compounds other than the polyphenols
may be responsible for the platelet inhibitory activity.
We recently examined the anti-platelet activity of
several fruits and this activity was not related to the
antioxidants potential of fruits.
Despite the fact
that kiwi fruit contain very significant amounts of
antioxidants such as polyphenols and vitamins C and
it was not included in the study. Recently it
has been shown that kiwi fruit provide a dual
protection against oxidative DNA damage, enhan-
cing antioxidant levels and stimulating DNA repair
and may be beneficial in cancer;
information is available on the effects of kiwi fruit
on platelet activity and plasma lipids, these two
important risk factors of CVD, in human volunteers.
In this paper we report that consuming of two or
three kiwi fruit per day for 28 days significantly
reduced platelet aggregation in human volunteers in
a randomized cross-over design. Moreover, plasma
triglycerides levels were also reduced in these
volunteers. Our study indicates that consuming kiwi
fruit (two or three per day) may be beneficial in CVD.
Materials and methods
Collagen, ADP and arachidonic acid were obtained
from Chrono-Log (Havertown, USA). Uric acid,
ascorbic acid, EDTA, acetic acid, sodium hydroxide,
metaphosphoric acid and phosphate-buffered saline
(PBS) tablets were obtained from Sigma (Poole, UK).
All other reagents used were of analytical grade
Thirty (12 males and 18 females) healthy volunteers
took part in this study. Volunteers were aged 20–51
years and their mean BMI was 22.43 0.52 kg/m
The volunteers were recruited by means of adver-
tisements at the Institute for Nutrition Research,
University of Oslo, Oslo, Norway. Volunteers were
requested to maintain normal diet during the trial.
Subjects were allocated randomly to two groups
(n¼15), each of which was given different order of
kiwi fruit doses. Group A took two kiwi fruit per day
in the first period and three kiwi fruit per day in the
second period, whereas group B took two and three
kiwi fruit per day. Each volunteer consumed two and
three kiwi fruit per day for successive 28-day periods
separated by at least 2-week wash-out periods. The
study protocol was approved by the Ethical
Committee of Ulleva
˚l University Hospital, Oslo.
Healthy subjects were recruited after assessment of
their medical and dietary history. Exclusion criteria
were the presence of overt vascular, haematological
or respiratory disease, hypertension, infection, fre-
quent consumption of drugs which affect platelet
function (e.g., aspirin, paracetamol, ibuprofen, ste-
roid, habitual consumption of omega-3 fatty acid
Preparation of kiwi fruit extract
In order to investigate the effects of kiwi fruit extract
on human platelet aggregation in vitro. Extracts
consisting of 100% fruit juice were freshly prepared
on the day of the assay from kiwi fruit. To prepare
100% fruit juice, the fruits were peeled and the pulp
after being weighed was homogenised. The resulting
homogenate was centrifuged at 3000 gfor 10 min.
The supernatant was collected and the pH was
adjusted to 7.4 with sodium hydroxide. The pH-
adjusted kiwi fruit extract (KFE) was then used for
in vitro platelet aggregation experiments.
Platelet aggregation study
Overnight fasted blood was collected through silico-
nized needles into plastic syringes: coagulation was
prevented by mixing 9 vol of blood with 1 vol sodium
citrate (final concentration, 13 mM). Platelet-rich
plasma (PRP) was obtained by centrifugation of
citriated blood for 15 min at 180 g. The supernatant
platelet-rich plasma (2–3 10
cells/ml) was collected
and used for platelet aggregation.
Platelet aggregation was monitored on a platelet
aggregometer (Chrono-Log) at a constant stirring
speed of 1000 rpm at 37C, as described before.
aggregating agents used were ADP (4 and 8 mM),
and collagen (4 and 8 mg/ml). Platelet aggregation
was followed over 10 min. Platelet aggregation was
performed within 2 h after the blood was taken.
Platelet aggregation is expressed as the area under the
curve. To determine the effect of KFE on platelet
aggregation in vitro, PRP (450 ml) was incubated with
50 ml of KFE for 15 min at 37C prior to the addition
of an aggregating agent. Since maximal amplitude
of aggregation of PRP was obtained with either 4 mg/
ml collagen, 8 mM ADP, and 500 mg/ml arachidonic
acid, these concentrations of agonists were used
and aggregation was followed as described above.
Controls were run in parallel replacing fruit extract
with 50 ml of PBS. Inhibition of platelet aggregation is
expressed as the decrease in the area under the curve
compared with the control.
In order to determine the effects of consumption
of kiwi fruit on platelet aggregation response in
human volunteers, blood samples were taken at
study entry (day 0), and after day 28 of fruit con-
sumption, between 08:00 and 10:00 h after an over-
night fast. PRP was prepared for platelet aggregation
experiments as described before.
288 KIWI FRUIT CONSUMPTION
Determination of plasma vitamin C
Blood was collected in heparin on ice and was
centrifuged at 2000 gfor 10 min at 4C. Then 600 ml
of plasma were mixed with 600 ml of 10% metaphos-
phoric acid in a tube and was snap frozen The
samples were stored at 80C until required for
determination of total vitamin C concentration
(vitamin C and dehydroascorbic acid) by HPLC, as
Ferric reducing/antioxidant power (FRAP) assay
The FRAP assay was performed according to Benzie
and Strain (1997).
The FRAP assay was used to
measure the concentration of total antioxidants in
plasma using Technicon RA 1000 system (Technicon
Instruments Corporation, New York, USA). An
intense blue colour with absorption maximum at
600 nm was measured.
Determination of plasma lipids
Plasma triglycerides, HDL and total cholesterol
concentrations were determined using reagents from
Genzyme diagnostics (UK) following the protocol.
LDL-cholesterol was calculated using the Friedwald
Results are presented as the mean SEM. Results were
analysed by the Student’s t-test. Values for the area
under the curve for platelet aggregation in the absence
and in the presence of different concentrations of
fruit extract were evaluated by a computer-assisted
programme. Other statistical analyses were per-
formed using ANOVA where appropriate, values
were considered to be significantly different when
Effects of kiwi fruit extract on human platelet
aggregation in vitro
One hundred percent kiwi fruit extract (KFE) (w/v)
was used in this study. Incubation of KFE (expressed
as weight of pulp used to prepare KFE) inhibited
ADP-induced platelet aggregation in a dose-
dependent manner (Figure 1). ADP-induced aggrega-
tion was inhibited by 11% with 5 mg KFE, 54% with
10 mg KFE, and 96% with 20 mg KFE, compared
with controls. KFE also inhibited collagen-induced
platelet aggregation, however, the level of inhibition
was lower with the 5- and 10-mg KFE incubations
compared with those observed with ADP-induced
platelet aggregation (Table 1). Inhibition of arachi-
donic acid-induced platelet aggregation exhibited a
very different profile with only 32% inhibition at the
highest KFE level (20 mg) tested, and nothing at all at
the lower concentrations of KFE. The IC
mum concentration required for 50% inhibition of
platelet aggregation induced by ADP in 500 ml PRP)
of KFE extract was around 10 mg KFE. The KFE
extract inhibited both collagen- and ADP-induced
platelet aggregation to a greater extent, whereas
it had very little inhibitory effects on arachidonic
Figure 1. Effect of different amounts of kiwi fruit extracts on platelet aggregation by ADP in vitro. PRP (450 ml) was incubated with
different amounts (0, 5, 10, and 20 mg) of kiwi fruit extract for 15 min at 37C prior to the addition of ADP (8 mM). For details, please see
Materials and methods. (A) Control; (B) 5 mg KFE; (C) 10 mg KFE; and (D) 20 mg KFE.
Effects of consumption of kiwi fruit on plasma
antioxidants in human volunteers
Of these 30 subjects, all except two volunteers
completed the two phases of kiwi fruit consumption.
During the supplementation period no significant
change in their mean BMI was observed. The kiwi
fruit were well tolerated without any adverse effect.
Dietary antioxidants (antioxidant levels, and total
vitamin C) were measured in plasma before and after
the trial period. Figure 2 shows that the plasma levels
of FRAP increased significantly after two or three
kiwi fruit per day. FRAP levels were increased very
significantly in both the groups after consuming
fruit (two or three kiwi fruit per day) (P<0.01),
although no statistically significant differences
between these two groups were observed. Similar to
FRAP values, plasma vitamin C levels in these
volunteers were also increased significantly, increas-
ing from 65.92 9.0 mM (day 0) to 102 23.1 mM
(day 28) (P<0.01) and from 68 15.2 mMto
92.38 14.7 mM(P<0.01) after consuming two and
three kiwi fruit per day, respectively.
Table 2 shows the platelet aggregation response to
different concentrations of ADP and collagen at day
0 and at 28 days after consuming two or three kiwi
fruit per day. Platelet response to both low and high
concentrations of ADP or collagen was inhibited by
kiwi fruit consumption. Consuming two kiwi fruit
inhibited ADP-induced platelet aggregation signifi-
cantly (18% in case of 4 mM ADP and 15% in case of
8mM ADP compared with those at day 0 (P<0.05).
Similar reduction in platelet aggregation in response
to collagen was observed when volunteers consumed
two or three kiwi fruit per day for 28 days (Table 2).
After the wash out period (minimum 2 weeks) platelet
aggregation response returned to the base line level
Table 3 shows the values of plasma concentrations of
total cholesterol, HDL, LDL, and triglycerides at day
0 and day 28. Mean total cholesterol, LDL, and HDL
cholesterol values in all groups were unchanged from
days 0 to 28 in both groups, whereas triglyceride
concentrations were significantly lowered on day 28
(1.16 0.45 mmol/l at day 0 vs. 0.87 0.29 mmol/l,
P<0.05, at day 28 and 1.19 0.35 vs.0.84
0.35 mmol/l, P<0.05, in the case where volunteers
consumed two and three kiwi fruit per day, respec-
tively), compared with those on day 0 in both groups
(P<0.05). After the wash-out period (minimum 2
weeks), plasma triglyceride concentrations returned
to the base line level.
The kiwi fruit extracts inhibited both ADP and
collagen-induced platelet aggregation in vitro, but not
arachidonic acid-induced aggregation, indicating that
the thromboxane pathway does not appear to be
involved, as we observed in the case of tomato
This is quite different than that of aspirin’s
mode of action in platelets. Aspirin’s anti-platelet
action involves inhibition of the cyclooxygenase
enzyme in platelets, leading to a decreased formation
of prostaglandin G
, a precursor of TxA
blocks the formation of TxA
, a platelet aggregation
agonist. Since kiwi fruit extract does not inhibit the
Figure 2. Effect of consuming kiwi fruit on plasma FRAP
values in volunteers. FRAP was measured in the plasma of
volunteers at day 0 and after consuming two kiwi fruit per day for
28 days. For details, please see Materials and methods.
Table 2. Effect of kiwi fruit consumption on platelet aggregation
Agents Two kiwi
fruit per day
fruit per day
Day 0 Day 28 Day 0 Day 28
ADP, 4 mM703.2 53 3.2* 69 1.8 55 2.1*
ADP, 8 mM693.1 55 4.1* 68 2.3 52 3.2*
Collagen, 4 mg/ml 68 4.2 52 2.3* 67 3.1 53 3.1*
Collagen, 8 mg/ml 70 3.9 51 4.3* 70 2.2 50 3.5*
For details please see Materials and methods, *P< 0.05.
Table 1. Mean percentage inhibition of platelet aggregation in
vitro by kiwi fruit extracts induced by three different aggregating
Kiwi fruit extract
Inhibition of platelet aggregation (%)
acid (500 mg/ml)
ADP (8 mM)
5 0 0.53 0.21 11 4.3
10 0 18 4.5 54 12
20 32 89611 96 14
For details please see Materials and methods.
290 KIWI FRUIT CONSUMPTION
thromboxane pathway, it is possible that the mode of
action is upstream of platelet activation/aggregation
processes. At present we do not know the nature of
the anti-platelet factors in kiwi fruit.
This study was, therefore, designed to assess the
effects of kiwi fruit consumption on the cardiovas-
cular risk profiles in healthy volunteers. Kiwi fruit
consumption increased plasma antioxidants and
vitamin C levels in these volunteers as expected.
Consuming two or three kiwi fruit reduced platelet
aggregation to a similar extent. In addition, con-
sumption of kiwi fruit reduced plasma triglyceride
levels without affecting cholesterol levels in these
volunteers. There were no correlations between
individual changes in platelet aggregation response
and plasma lipids and vitamin C values. In addition,
the magnitude of these effects of kiwi fruit is not
related to the number of kiwi fruit consumed. We do
not have any explanation for this. The inhibitory
effects on platelet aggregation response and lowering
effects on plasma triglyceride levels of kiwi fruit
disappeared during the wash-out period. This indi-
cates that the effects of kiwi fruit on platelets and
plasma lipids are reversible. We restricted our study
with relatively small number of kiwi fruit (two, or
three), as consuming larger number of fruits is known
to have laxative effect. However, further work is
necessary to determine the structure and mechanism
of action of the active principles in kiwi fruit
responsible for lowering platelet aggregation
response as well as plasma triglycerides in humans.
Epidemiological studies as well as laboratory
experiments have provided very strong evidence
that fruits and vegetables and specific antioxidants
are beneficial for human health.
effects of vegetables and fruit may in part be
attributed to antioxidant vitamins and specific poly-
phenols that display powerful inhibition of oxidative
stress. However, we have earlier reported that the
anti-platelet potential of the fruits appeared to be
unrelated to their antioxidant activity.
further research on identification of the active
compounds requires for definitive conclusions.
Given the role of blood lipids in the development
of atherosclerosis and CVD and the positive roles of
fruits and vegetables on plasma lipids,
also assessed the effects of kiwi fruit on plasma lipids.
Lowering of plasma triglycerides by kiwi fruit was
observed despite these volunteers maintaining their
regular diet during the supplementation periods.
None of the volunteers reported any loss of appetite
or changes in their food intake during the supple-
mentation. The mechanism of action is not known; it
is possible that the presence of certain components in
kiwi fruit may be responsible for the lipid-lowering
effects. However, further work is required to under-
stand the mechanism of action. It must be noted that
the lipid-lowering effects of fruits and vegetables were
also reported before.
In conclusion, consuming kiwi fruit is an effective
way of inhibiting platelet aggregation induced by
collagen and ADP in human volunteers. Our data
thus provide evidence that consuming kiwi fruit has
the potential to increase the effectiveness of throm-
bosis prophylaxis. Modulation of platelet reactivity
towards collagen, ADP and plasma triglyceride levels
by kiwi fruit could be of potentially prophylactic
and therapeutic benefit in preventing and halting
pathological processes that lead to CVD.
This work was supported by the International Kiwi Fruit
Organization (IKO). We are thankful to Mr Hamid Shergafi for
his technical assistance and Ms Anette Karlson for vitamin C
analysis. We are also grateful to BAMA, Norway, and Zespri,
New Zealand, for supplying us kiwi fruit for this study.
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292 KIWI FRUIT CONSUMPTION