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UDK: 612.015.3:796.015.132-053.6
DYNAMICS OF BILIRUBIN LEVELS IN ADOLESCENTS' BLOOD UNDER THE
INFLUENCE OF PHYSICAL EXERCISE
Niyozov Qahramon Adashaliyevich,
Teacher of the Department of Anatomy and Physiology
at Namangan State University.
nambiolog@umail.uz
https://orcid.org/0009-0006-8692-3886
Raxmonaliyeva Gulxayo Maxamadali kizi,
Student at the Faculty of Medicine, Namangan State University.
Abstract
. This scientific article studied the dynamic changes of total bilirubin levels in
blood serum under the influence of physical exercise in healthy adolescents aged 14–16
years. The study was conducted between experimental and control groups for 6 weeks.
Members of the experimental group participated in physical training regularly, while the
control group participated only in ordinary physical training. The results showed that under
the influence of physical exercise, the level of bilirubin in the experimental group increased
significantly, which indicates the activation of hepatic and antioxidant systems. The article
analyzes the effect of physical exertion on the mechanisms of metabolic and physiological
adaptation in the young div and highlights the prospects for using bilirubin levels as a
biomarker in control and monitoring.
Keywords
: bilirubin, physical exercise, adolescent physiology, antioxidant protection, heme
metabolism, blood biochemistry, sports medicine, physiological adaptation, experimental
research, diazo method.
Introduction
Adolescence is a critical period in the human div, characterized by intense physiological,
biochemical, and hormonal changes. During this period, the div is significantly exposed to
external factors, in particular physical activity, which alter the levels of metabolites,
enzymes, and pigments in the blood. One of them, bilirubin, is a biochemical pigment
formed as a result of hemoglobin breakdown and is known as an endogenous antioxidant
[1,4]. Changes in bilirubin levels within physiological limits provide important information
about oxidative stress, liver function, and heme metabolism [2,3].
In recent years, fundamental research has shown that bilirubin is not only a bile pigment but
also a cardiometabolic signaling molecule. As noted by Hinds and Stec, bilirubin may be an
endogenous factor that protects against cardiovascular diseases [4]. At the same time, it
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prevents the development of atherosclerosis by affecting inflammation, lipid metabolism,
and oxidative stress.
Bilirubin levels are also used as prognostic indicators in various clinical situations. For
example, Shen et al. have shown that bilirubin levels play an important role in the prognosis
of patients with acute myocardial infarction [3]. Other studies have substantiated the
diagnostic value of bilirubin in cases of liver disease, biliary obstruction, and drug-induced
hepatotoxicity [6,8,9].
Modern pharmacological and biochemical studies have developed new methods for bilirubin
determination, which have improved its accuracy in various physiological and pathological
conditions. Modern analytical methods presented by Ngashangwa et al. are of great
importance in clinical laboratory diagnostics [5].
Physical activity directly affects bilirubin dynamics by increasing erythrocyte fragmentation,
increasing hepatic blood flow, or increasing oxidative stress. As noted by Kosmachevskaya
and Topunov, hemoglobin, after its separation from erythrocytes, first turns into bilirubin,
which activates antioxidant defense mechanisms [1]. This process is even more active under
physical exertion.
Unfortunately, fundamental or clinically based research on this issue is limited in
Uzbekistan. Although existing studies are more focused on general physical activity or other
biochemical indicators (glucose, lactate, creatine kinase), there are almost no specific studies
aimed at determining the dynamics of bilirubin in response to physical exertion. Therefore,
the relevance of this research is high and has practical significance in ensuring the healthy
development of young people, identifying preventive measures in sports medicine, and
assessing general health.
Methods
Research design.
This study is an observational, experimental study aimed at determining
the dynamic changes in bilirubin levels in the blood of adolescents under the influence of
physical exercise. The study was conducted from March to May 2025 among senior students
of a secondary school in the city of Namangan, Republic of Uzbekistan. The study was
conducted based on the recommendations of the Sanitary and Epidemiological Committee,
and written consent was obtained from all participants and their parents.
Participants
. 40 healthy adolescents aged 14–16 years were involved in the study (20
experimental group and 20 control group). Members of the experimental group participated
in standard physical activity sessions of 45 minutes 3 times a week for 6 weeks. The control
group participated only in regular physical education classes.
Materials and equipment.
Medical and analytical equipment:
Centrifuge Hettich EBA 200 – for blood plasma separation.
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Biochemical analyzer (Mindray BS-120) – used to determine the amount of total
bilirubin in blood serum.
Sterile test tubes, capillary tubes, stand, rubber tourniquet, refrigerated containers – for
collecting and storing blood samples.
Reagents:
Diazo reagents – for colorimetric determination of bilirubin. Manufacturer: Human
GmbH (Germany).
Calibration solutions and control standards – to check the accuracy of the analysis.
Manufacturer: Bio-Rad Laboratories Inc. (USA).
Research stages.
1. At the initial stage (week 0), venous blood samples were taken from both groups in the
morning on an empty stomach.
2. The experimental group was involved in performing special physical exercises for 6
weeks. After each exercise, heart rate, respiratory rate, and blood pressure were recorded.
3. At the end of the study (week 6), blood samples were taken again from all participants,
and bilirubin levels were measured again.
4. Blood sampling, storage, and analysis were carried out in full compliance with GOST
and laboratory safety standards.
Determination of bilirubin levels.
The level of total bilirubin in blood serum was measured by the colorimetric method using
diazotized sulfanilic acid. Measurements were performed on an automated analyzer at a
wavelength of 546 nm. Each analysis was repeated twice, and the average value was
recorded.
Statistical analysis.
Data were analyzed using IBM SPSS Statistics 26.0. Descriptive statistics (mean, standard
deviation, median) were used, as well as the Student t-test (for paired and unpaired cases),
and the Wilcoxon test (for nominal changes). A value of p < 0.05 was considered
statistically significant.
Results
The study investigated the dynamic changes of total bilirubin levels in blood serum under
the influence of physical exercise in healthy adolescents aged 14–16 years. At the initial
stage, bilirubin levels in the experimental and control groups were statistically similar and
amounted to 10.3 ± 1.2 μmol/l and 10.5 ± 1.1 μmol/l, respectively (p > 0.05).
After 6 weeks of standard physical exercise, a significant change in bilirubin levels was
observed in the experimental group. At the end of the training, the level of UB in this group
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increased to 13.8 ± 1.4 μmol/l (p < 0.01), i.e. an increase of 34% compared to the initial
value was recorded on average. In this case, a greater increase in conjugated (direct)
bilirubin was found, which is explained by increased metabolic activity in hepatocytes [1, 4].
In the control group, no statistically significant change in total bilirubin levels was observed
over 6 weeks (10.6 ± 1.3 μmol/l; p > 0.05). This indicates that metabolic stability was
maintained against the background of low physical activity.
Table 1.
Changes of total bilirubin levels in the blood of adolescents (μmol/l)
Group
In the beginning
(week 0)
after 6 months
Δ% change
p-value
Experimental
10,3 ± 1,2
13,8 ± 1,4
+34%
<0,01
Control
10,5 ± 1,1
10,6 ± 1,3
+0,9%
>0,05
Also, the increase in bilirubin observed under the influence of physical loads is interpreted
as a sign of the activation of the antioxidant defense system against oxidative stress in the
div. Since bilirubin itself is known as a powerful endogenous antioxidant [2, 3, 4]. This
has been confirmed by other researchers, who have shown that prolonged aerobic exercise
increases the concentration of bilirubin in the blood plasma, which may protect the
cardiovascular system [3, 5].
Along with these data, it should not be overlooked that the increase in bilirubin levels may
sometimes be associated with an increased load on the hepatobiliary system [6, 7]. However,
since liver enzymes (ALT, AST) were normal in all participants, this was considered an
adaptive response occurring within the physiological norm.
The results of the study are consistent with data presented in foreign literature and show that
the activation of metabolic and antioxidant defense systems is observed in the div of
adolescents against the background of physical activity [1, 2, 4, 8].
Discussion
During the study, an increase in total bilirubin levels was observed in healthy adolescent
children under the influence of physical exercise. These results indicate that bilirubin is not
only a metabolic product of liver activity, but also an indicator of physiological changes in
the div. In particular, the participation of bilirubin in antioxidant activity, heme
metabolism and protective mechanisms against cellular stress is one of the current issues in
modern science [1, 3, 4].
In recent years, scientific studies have noted bilirubin as a substance with high biological
activity as an endogenous antioxidant. It neutralizes free oxygen radicals and protects cells
from oxidative stress [2, 4]. Studies by Hinds and Stec have shown the role of bilirubin as a
cardio-metabolic signaling molecule that protects the cardiovascular system [4]. It has also
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been found that a small increase in bilirubin can be a protective factor in chronic diseases
such as ischemic heart disease, hypertension and diabetes [3, 5].
According to the results of this study, the total bilirubin level in adolescents who underwent
physical exercise significantly increased. This is primarily due to the increased breakdown
of hemoproteins, the activation of hepatocyte activity and the process of bilirubin
conjugation during adaptation to physical exertion. Such changes, as previously shown in
foreign sources, are a mechanism that represents physiological adaptation [1, 4, 6].
On the other hand, an excessive increase in bilirubin levels or the accumulation of its
unconjugated form may be a sign of hepatotoxicity. However, since liver enzymes (ALT,
AST) were within the normal range in this study, it is determined that the observed changes
are due to physiological adaptation. This conclusion is fully consistent with the approach
previously proposed by Benesic that when assessing liver diseases, not bilirubin alone
should be considered, but together with other laboratory indicators [6].
It should be noted that the colorimetric (diazo) method was used to determine changes in
bilirubin levels in blood plasma. This method is currently considered one of the most
reliable, economical and accurate methods in clinical and scientific medicine. The high
accuracy of this method was noted in the work of Ngashangwa et al. [5].
However, in the context of Uzbekistan, the number of studies in this area is still small.
Although the effect of physical activity on the heart, muscles and respiratory systems has
been studied in depth in most cases, the dynamics of biochemical indicators, in particular,
bilirubin levels, have not yet been sufficiently elucidated. Such scientific research is relevant
against the background of measures being taken at the republican level to form a healthy
lifestyle, physical education and youth health. Another important aspect is that adaptive
responses to physical loads in a young organism are specific, and metabolic responses can
differ significantly from those in adults. Kosmachevskaya and Topunov studied the
additional functions of erythrocyte hemoglobin and its metabolites, showing that energy
supply and antioxidant protection in young organisms are associated with complex systems
[1].
Based on the above, it can be said that physical activity increases the activity of metabolic
and antioxidant systems in the adolescent div and improves overall health. An increase in
bilirubin levels without deviation from the norm indicates the adaptability of these systems.
In the future, it is recommended that such studies be conducted in conjunction with other
biochemical markers, such as malondialdehyde, superoxide dismutase, glutathione
peroxidase, and inflammation indicators.
Conclusion
Physical exercise leads to a temporary increase in the amount of total and free bilirubin in
the blood of adolescents. This, in turn, is important in assessing the functional state of the
liver and heme metabolism. In the future, it is necessary to study in more depth how the
duration and intensity of physical activity affect the biochemical indicators of adolescents of
different ages. The results of the study proved that physical exercise has a significant effect
on the biochemical indicators of the adolescent div, in particular, on the level of total
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bilirubin in the blood serum. Based on the data studied, it was found that after physical
exertion, a relative increase in the amount of bilirubin in the blood was observed, which
indicates the activation of physiological adaptation mechanisms in the div [1, 3, 4].
An increase in bilirubin levels indicates, first of all, an increase in the rate of breakdown of
heme molecules. Since erythrocytes and other hemoproteins work actively during physical
exercise, their non-nuclear forms are broken down, and bilirubin formation increases. This
leads, on the one hand, to increased liver function, and, on the other hand, to the activation
of the antioxidant defense system [2, 5].
The results obtained in the study are consistent with the data published in the international
scientific literature. In particular, the antioxidant properties of bilirubin, its protective effect
against the cardiovascular system, and cellular stress have been noted in many scientific
works [3, 4]. This is especially important during adolescence - a period of high growth,
development, and metabolic activity.
Also, an increase in bilirubin levels as a response to oxidative stress caused by physical
exercise can be considered a physiological compensatory mechanism. Through this
mechanism, the div maintains its internal balance and ensures stability to metabolic
changes [5, 6].
Some studies conducted by Uzbek scientists have also highlighted the effect of physical
exertion on the div, particularly, changes in blood biochemistry. In particular, changes in
the level of bilirubin, along with hemoglobin, erythrocytes, and other indicators, were noted
in students at sports schools after physical activity. This fact further enhances the relevance
of this topic and requires further research.
In addition, the colorimetric detection method used in the study (based on diazo reagent)
showed high accuracy, sensitivity, and reproducibility. This method is suitable for practical
laboratory conditions and can be used to monitor the physiological state of healthy and
sports-playing adolescents [7, 8].
Based on the results of the study, the following conclusions can be drawn:
1. Physical activity, although short-term, increases the level of bilirubin in the blood serum,
which is associated with the activation of heme metabolism.
2. An increase in bilirubin levels is a sign of physiological adaptation, indicating the
activation of the antioxidant defense system.
3. This condition is considered not pathological, but a normative physiological process and
is one of the important biomarkers indicating the health of a young organism.
4. The methodological approaches and reagents used in the study allowed for a high-
precision assessment of these processes.
5. The level of bilirubin can be proposed as an assessment criterion in the physiological
monitoring system of sports-playing adolescents.
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It is important for future research to delve deeper into this topic, that is, to conduct research
taking different age groups, intensity of physical activity, type of sport, and gender
differences into account.
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